Quite a bit higher! Also not sure about the Wood Track recommendation. That is pretty Niche though.

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Heath Dotson
HD Coaching:Website |Twitter: 140 Characters or Less|Facebook:Follow us on Facebook

Ditto... a boatload higher than I expected. My "Mild Pavement" recommendation is 101 PSI on a 25mm tire.

15 psi higher than I thought he would recommend. 100 psi for my fat ass is more than the rated pressure for my 7.8's.

Doesn't work... Keeps telling me to fill out the form info to use the calculator. Then nothing happens... I just see the same form again.

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What's your CdA?

Yeah its a bit glitchy. I just refreshed the page after a few minutes and it worked.

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Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
Deals on Wheels - Results, schedule, videos, sponsors

I took "lbs" off weight and it worked

Yes, same here. Basically in the 99 to 100 psi on the 25mm tires. Weird that it does not differentiate between latex, tubeless, etc setups.

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Next races on the schedule: none at the moment

I was at IM Florida a few weeks back helping some people pump up their tires after I was done since I had a pump. Every single European told me they wanted at least 120psi and I probably helped 6 or 7 people. One guy asked me if I was sure I wanted to pump my tires only to 100psi. I started second guessing myself but I held to my 100 tho.

Are people using the actual measured tire width or the stated tire size? It says measured, which you can pretty much add 2mm to the stated size if you don’t have calipers.

My complaint is there’s no rough & smooth chipseal option. That’s got to be somewhere between old asphalt and cobbles. Also surprised to see lower pressure recommended for smooth gravel than cobbles.

Those variables shouldn't effect tire pressure choices (except maybe cobble for tubed setups if you are at risk of bottoming


Second---be sure you are using actual measured width on your wheels as measured with calipers. My 23mm on Roval is like 27mm actual

Cobbles are a different beast. Can be bigger hits but lower frequency. "Smooth Gravel" is probably not dirt, more like heavy cinder/ small pebbles. Much higher frequency of deformation.

Hopefully Josh can chime in, because this is not really lining up with his previous recommendations or my experience.

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Heath Dotson
HD Coaching:Website |Twitter: 140 Characters or Less|Facebook:Follow us on Facebook

My real world experiences aren't lining up with the calcuations either.

The calculator is putting me 10-15 Psi high on my road setup and 5-8 Psi low on my gravel setup(s)

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_______________________________________________

In what way does it not line up with your experience?

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Ed O'Malley
www.VeloVetta.com
Founder of VeloVetta Cycling Shoes
Instagram • Facebook

The calculator has me up around 100psi on conti 23s (yes, I even used 25mm in the calculator), and the ride is quite uncomfortable and a bit jarring that high. My by feel pressure for comfort, cornering, and flat protection is 80-85 psi.

My usual gravel tire setup is 650x42 and he calculator has me in the 25psi range. There would be too much squirm at this pressure and definitely a high risk of flatting. My usual pressure is around 30 -32 psi for my 42mm setup.

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On the 7.8's website they recommend pressured up to 115 psi (23mm and 250 lbs) and the wheel manual says 125psi is the max. Where are you seeing a 100 psi limit?

Looks like I am wrong. Not sure why I thought they were maxed out at 87 psi? I will take another look at my manual, but online it definitely says they can go much higher

Well, Josh is like the world's expert on bike tire pressure and he has tons of real measured data of different tires, wheels road surfaces, riders... I would trust that a lot more than personal feel, assuming you fill it all out correctly. I use gp5000 23c tires but they measure 26mm on my wheels. Hardest thing to know is exactly what he means by "mild asphalt" etc...

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Ed O'Malley
www.VeloVetta.com
Founder of VeloVetta Cycling Shoes
Instagram • Facebook

I am with you, Sean. I'd like to have guesses at more 'real world' types of surfaces and mixes. How about really narrowing it down to 50% old asphalt/50% chip-seal and other choices like that so we can really make more informed 'guesses'. I don't think I have any cobblestone races coming up...And while I'm whining like a biatch, how about adjustments for dry/light rain/heavy rain.

And everyone should use measured widths-come on really? Do people not own a paper clip and a ruler??


For the record, it's about 5-10 psi higher than what I currently use, and I'm also a bit surprised by that.

If you listen to Josh’s podcast, he has detailed how to set your tire pressure by feel for road. He basically says you keeping going lower until you get squirm in the corners or others negative handling trails, and go up a bit from there. I have verified my road pressure with Josh’s ‘by feel’ method.

No need to go into detail on the gravel pressure side of things, but if the terrain you ride and the way you ride requires a certain pressure not to flat, and you don’t want to use more volume for various reasons, then you get a pretty damn good feel for off pavement pressure.

I’m sure Josh would agree, the calculator is giving you a good starting place and it’s up to the user to adjust up and down from there based on their actual conditions, speed of riding, and riding style.

For me I was just surprised the numbers were quite far from the pressures I’ve concluded to work best for me.

Edit: I forgot to mention, I am a Josh/Silca fanboy 😃

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The numbers suggested for me were about spot on from what i use. The zipp tyrewiz app suggests a bit lower.

Edit: I read this backwards.

Yeah, bizarre.

I find it lower, but pretty much in line with what I previously evaluated from the "V shape" graph presented previously on their blog, for same tyre, wheel size and weight, on medium quality road.

From "V shape" graph ("official 25mm" GP4000sII on 17mm wheel - so probably wider - if I remember well ?) : optimal around 95 PSI

From calculator (based on 27mm measured "official 25mm" GP4000sII on 17mm wheels) : 86/87 PSI

From the french side :

With cobbles, lower pressure is better (speed wise), but the problem is : you broke wheels. Or you need to have a really large tyre.
If tyre deformation is smaller than cobbles "height deviation", with low pressure you broke the wheel.

This will not happen with smooth gravel, so you can really adjust the pressure lower for speed, not dealing with rim destruction risk.

See the "cobble" graph here : https://blog.silca.cc/...ressure-optimization

There is clear indication that a lower pressure will be better for speed.... but....

This is the reason for suspended bikes on Paris-Roubaix : increase flexibility to deal with cobbles "height deviation" above tyre deflection.

Maybe this is the statement we all seem to be missing:

“Surface Type: We recommend optimizing for the worst surface you are riding as you are generally better to be a bit low than to be a bit high.”

Although we generally have good roads around here, they vary from new to sometimes “smooth” chip seal. I have found the old pavement pressures line up pretty close to what I run on a daily basis.

---

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Heath Dotson
HD Coaching:Website |Twitter: 140 Characters or Less|Facebook:Follow us on Facebook

Ah yeah, I didn’t think about the rim damage aspect.

Ok, so let’s try and help provide a solution rather than just complain. How would everyone else like for the surface descriptions to progress?

I can only speak to roads, but my experience is this from smoothest to roughest:

Concrete
Smooth new asphalt
Old worn asphalt
Old smoother chipseal
New rough chipseal
Poorly laid chipseal that resembles gravel

Alright, sorry for being offline yesterday, we launched this and immediately had problems with the site and once the first people started sharing it, we spent the rest of the day trying to fix it and answer the emails and phone calls.. 4,000 people got the notification, after 1 hour, 15,000 people worldwide were tying to access it.. total cluster, so sorry to everybody who had a poor experience. The goal was to have a more interactive calculator with images and explanations etc, but once it was crashing like crazy we simplified and are now in process of putting it back together.

Answers for some of the questions and an idea of the future plan:

1. Numbers seem weird - Try it today, we had a term in an equation meant to go active in a later version with an additional feature that wasn't zeroed out, so pressures for the first handful of hours were probably trending a bit higher for narrow tires and lower for wider ones.. not by much, but by a few% for sure. This is fixed

2. Surface types - this has been the biggest question and we are working on providing images for each surface as our language is not consistent here. In reality, there are hundreds of options here and we are trying to make a gradient out of them. There is a blog post in the works on this for the official go live of the calculator that will have photos.. also open to ideas on the language as everybody seems to disagree here.

'New Pavement' - think of this as having being paved a few weeks ago using high quality fine aggregate fill, super smooth, low void.
'Mild' pavement as having some visible imperfections, cracks, and undulations, could also be newly paved with large aggregate fill, visible voids.
'old pavement' as being most any road in the midwest, visible cracks, small-medium potholes, occasional damage, 'alligator skinning'
'Cobbles' - Paver bricks to paver stone cobbles, also mild-medium aggregate chip-seal
'Mild Gravel - packed dirt' - This is packed dirt with mild-medium aggregate gravel over top. This is a deformable surface so more efficient to allow the tire to deform more rather than deforming/disrupting the surface. Could also be coarse chip-seal (uncommon)
'Coarse Gravel' - large aggregate or large embedded imperfections like Dirty Kanza flint

3. Measured tire width - This is in fact the measured width of the installed tire at the casing (graphic pulled and coming back soon). It is hard even for me, dealing with this stuff every day, to keep this one straight as we continue to call the tires by their casing numbers, but I have some 23mm GP4000SII on some ENVE with 21.5 inner bead width that measure at 28.9mm wide, so would be 29mm in this calculator. Opposite of that, many of the gravel and mtn tires measure at or below the casing number which seems to be a combination of assuming wide bead seat rims and/or measuring to tread and not casing, for example WTB Riddler 29x2.25 (57mm) actually measure 51mm at the casing (I get 56-57mm at the tread) on the ENVE G23 rim.. so that measured casing number is critical. We also have a piece on this that will make it's way onto the calculator once we are stable.

4. Speed - lastly, we are building in a speed component to further help the discussion and that will also bring a pinch flat risk calculator to the equation. As we often find with the pros, the final pressure is often slightly higher than what you might expect due to the increased energy at which they hit things increasing pinch flat or damage likelihood. Also tire behavior is related to dynamic, rather than just static stiffness, so breakpoint pressure will move higher with higher velocity and lower with lower velocity. As the data in this calculator is almost exclusively taken from ProTour and top level triathlon competitors, the speeds ridden in compiling this data are likely higher than what most of us are riding!

Best and please keep the feedback coming
Thanks
Josh

---

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Awesome. Thanks for the explanation. In playing around with it a little more I'm starting to see some numbers I more expected to see. In particular at my weight and 26mm, I found the mild vs old pavement numbers interesting and more in line with what I thought: 90psi for mild, 83psi for old. Waco 70.3 last month would have definitely fallen in the old but Indian Wells 70.3 next month will be mild-good.

On a side note, I finally broke down and ordered a Viaggio Travel Pump today. Figured there wasn't much point in knowing the right numbers if I'm not pumping up to the right numbers. No more sharing my pump in transition with the other pros now :P

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Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
Deals on Wheels - Results, schedule, videos, sponsors

Gave the pressure calculator a try, but even for mild pavement (with system weight 172lbs), its recommending 93psi for 25mm measured width tires. I'm using Hed jet plus wheels with 23mm gp5000 tires, and Hed says their rims are not rated for above 90psi. Are the hed rims unique in pressure required, or is the recommendation too high? Very cool idea though, thank you for making available!

Are you sure you are measuring 25mm for your tire on a HED wheel? Are you running a tire spec'd as 21mm width? I would imagine that a 23 or 25 spec'd tire would be a good bit wider on a HED wheel.

Thanks much. I have been waiting for this for a while.

One question: Does the tire width and rim width make a difference here? For example, two tires measuring the same may have dramatically different volumes. Take a hypothetical wide tire on a skinny rim that measures 26mm actual versus a narrower tire on a nice, fat, wide modern rim that also meaures 26mm. Should those two tires measuring the same width but with different volumes get different pressures? Do we need a height and width here?

The rim is 25mm outer diameter, and the 23mm tire does not balloon out. I think when I checked it with calipers is was 24. something, its a pretty flush fit with side of rim

If both tires measure the same diameter at the widest point, then the volume of the tire above the rim ought to be nearly identical. But, there could be some difference in total volume, like with HED rims that have a deeper and wider interior channel below the tire.

Wow. I didn't realize this was a thing

I just pump it up to what it says on the side and ride all day [stopping at Wawa every now & then]

---

"What's your claim?" - Ben Gravy
"Your best work is the work you're excited about" - Rick Rubin

You triathletes and your tyre pressures. 😂

That's a suggested max pressure. HED jets are AL rim. You're not going to hurt the rim pumping it up higher than the recommended.

The GP5000's are sized for newer rims. I'd suggest going with 25's on the jet+. The new 25 measures about like the old 23 GP4000.

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Heath Dotson
HD Coaching:Website |Twitter: 140 Characters or Less|Facebook:Follow us on Facebook

Josh;

4,000 people got the notification, after 1 hour, 15,000 people worldwide were tying to access it.. total cluster, sorry to everybody who had a poor experience

I guess the good news, is that alot of people are following you and your work !

Thanks for your work.

Thanks for the suggestion. Even with the change to a 25 though, the tire pressure recommendations (per rider weight) on the Hed site recommend me in the mid 70s for tire pressure. Its a pretty big difference

Pressures for my road bike are very close to what I run. A couple pounds higher for the rear and ten pounds higher for the front. I'll try the slightly higher pressures.

For my gravel bike (both 38mm and 47mm tires), the recommended pressures are very low compared to how I race. I suspected they would be, though. I fear the pinch flat and, historically, have kept my gravel tires up around 50 to 55 psi. I'll try slightly lower pressures, but I'm not sure I'll ever get down to 32psi and 24psi. (I'm not saying they aren't the right pressures. I'm just saying I'm probably too chicken to get down to those numbers.)

I think this is a great resource. The problem with it is going to be user error, in that 90% of the people that use it will not actually measure the width of their tire and will go by the printed number on the sidewall. Or if they measure it they're going to hold a tape measure somewhere nearby and eyeball it, and their innate biases will lead them to say it's 23 mm wide when it's really 24 or 25 mm wide.

All of which means that most folks are going to still keep on doing what they do now, which is to pump their tires up too high. Tradition dies hard.

The user needs to be really hit on the head about actually measuring the width. And then hit again. Then you'll start making progress but you still need to hit them over the head again. And again.

\

so, is everyone using a micrometer to measure tire width? I didn't realize I needed one in my tool kit. I imagine there is going to be a run on Amazon. Anybody have one they like?

Did you not realise. 😂😂

Also a pump to adjust pressure to 0.1psi

And a thermometer to measure the tread temp and internal tyre temp for further adjustments.

If you're not checking and adjusting it every 2km you're so 2010.

🙄🙄🙄

As long as you like to keep unnecessarily wasting watts, I hope you’re in my age group

At the intersection of affordable and decent quality we're recommending these:

Analog Calipers

Digital Calipers

The ones we use in our lab

Everybody should have a set really, you will find all sorts of uses for them and they come in handy for all sorts of things that you probably aren't thinking about yet.

---

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Oh come on. I gave at least a dozen calipers (as a cardiologist) and I don’t need ‘calipers’ to measure a tire. Bend the paper clip so it’s pretty close to the width of the tire and place it against a ruler.

Measured tire width!!

Boom

That works too.. but WAY less fun that having calipers ;-)

---

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

God, don't encourage them Josh!!! :D

I will also add that calipers are the best/easiest way to verify the rule of 105..
A pair will help ensure that you aren't making some simple size and pressure errors with tire choice.
Considering that the penalty of getting these things wrong is probably 3-5x more than you would save by dropping hundreds of $$ on ceramic bearings or the like, the $35 calipers seem like a pretty good value!
J

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http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Hi Josh, one thing that I note is that the 48/52 weight distribution is probably true for a pro with a slammed set up.... most mortals are not riding that ratio. My simple trial, ie scale under the front wheel zeroed then sit on the bike and see how much of my weight shows up on the front. (the set up was on a trainer and the bike somewhat leveled) said that my normal on the hoods situation was no where near 48/52 but closer to 40/60. I also note that the ratio of air pressure is not a constant depending upon the tire width but that is not a huge thing because most pumps are only good at +/1 psi (that is the minimum reading), but the numbers change with tire width.

So I suggest another addition and that is for riding on the hoods vs drops and most people spend most of their time on the hoods so that changes the front back weight ratio.

ps, BTW I have a couple of pairs of digital calipers and they cost (on sale) less than $20 and I use them a lot. My 25mm Conti 4000IIs are 25.5 and 25.9mm measured at pressure. The fatter tire is on the rear....

Josh, is optimal pressure for two difference width measurements as simple as running the calculator twice and taking the front/rear value or is there something else we should consider there?
As it stands, with my current setup I would be running 86psi rear and 100psi front (27mm/24mm measured).

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Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
Deals on Wheels - Results, schedule, videos, sponsors

😁🙏🏼👏🏼

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https://www.strava.com/...tes/zachary_mckinney

Does the 105 rule matter much for rear wheels? It’s been a while since I looked at it so I can’t remember if you addressed that, but I thought the rule related to aero properties so might not apply to rear wheels (as much?)...????

Is it still offline?
I get 'no options' for tyre width.

Link doesn't work although I submitted my info.

Yes, you can run it 2x with different widths and use the respective front/rear value for that size in your setup.

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http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

The Rule of 105 also matters for rear wheels, but definitely to a lesser effect. As the front half of the rear wheel is either shielded or running in pretty turbulent air, that part of the system isn't as sensitive to 105. However, if you are running a deep wheel or disc, having the tire narrower than the rim really helps that flow close up much tighter than if the tire is at or wider than the rim. These effects are probably a watt or so for most setups and most yaw angles, so not huge, but also non-zero.

---

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Interesting results for me: according to the calculator, I've been running the pressure on my road bike about 10+ PSI too low (I'm running 70 PSI front / rear, and the calculator is giving me low to mid 80s depending upon the surface). I will have to bump the pressure to more closely match the calculator, and see how things go.

Josh - the one thing I don't see in the calculator is the tire construction. Does this matter at all? Does tubular vs. tubeless vs. butyl tube vs. latex tube affect the recommended pressure? If so, how? Intuitively I would think these would, as they will change the stiffness of the tire.

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Matthew
Twitter: @AlphaDogCycling
Instagram: @AlphaDogCycling

The Pro Version is now out. Just got the email and playing around with it now. Definitely nice guide to pavement quality.

Edit: after playing around with it it seems like the pressure guides are even a bit higher than the previous version.

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Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
Deals on Wheels - Results, schedule, videos, sponsors

Pressures seem about right when I put in 25mm tires. They seem a little high for what I run when I put in 32mm tires.

And definitely like the additional granularity in the different surfaces.

The gravel pressures are a lot higher in this pro version. i personally feel like the original aligns more with my previous experience, but YMMV

Rob,
What settings are you seeing as quite different? I just ran a handful of gravel scenarios in both calculators side by side and am getting nearly identical numbers? So in the original we had 'coarse gravel' which was in between Cat3 and Cat4 gravel on the new calculator and mild gravel which was sort of between cobbles and cat3 gravel in the nw calculator. The underlying algorithm is the same between them, we are just trying to refine the way that the surface roughness is defined by the user.

If you haven't tripped it up yet, there is also a pretty slick pinch flat predictor running in the background based on rider velocity and impact energy that will let you know if your optimal pressure is getting too close to, or beyond the danger zone for your weight/surface/speed.

---

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

"Mountain bike" recommendations are quite low

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I talk a lot - Give it a listen: http://www.fasttalklabs.com/category/fast-talk
I also give Training Advice via http://www.ForeverEndurance.com

The above poster has eschewed traditional employment and is currently undertaking the ill-conceived task of launching his own hardgoods company. Statements are not made on behalf of nor reflective of anything in any manner... unless they're good, then they count.
http://www.AGNCYINNOVATION.com

I guess it could have just been my original interpretation of the surface conditions. I was looking at coarse gravel before, which gave me 32.6f psi and 34 rear for 39mm tires at 185lb system weight. That’s right on the high end of what I’ve found to be comfortable on most normalish gravel roads.

I was then looking at cat 3 gravel in the pro system, but now I realize that’s not really an apples to apples comparison. The calculator is 2.5 psi higher. But cat 4 is pretty similar to what the other one said for coarse gravel. So I was wrong in saying the pro was way higher... I was just using it incorrectly.

To me 35/36.5 sounds a little high for a tire that wide on roads that look like the cat 3 photo. But, a little high is safer than slicing a tire with your rim on a hard hit...so probably not horrible advice.

For several years I've been running around 20 front/25 rear, the recommended pressure I got was 22 rear/20.5 front. And that's with me being a Clydesdale, on 26"x2.2" tires. So at least for me the results seem reasonable...

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"I'm thinking of a number between 1 and 10, and I don't know why!"

Josh, I still fear that this version doesn't make it clear enough that you need to actually measure the width of the tire for this to work. Most complaints I have seen about the calculator seem like they come from people who maybe are just reading the sidewall of the tire.

This was my thought (at least since so many appear to be saying they need to inflate way more based on this calculator, which strikes me as unlikely). When I did my calculations, I was about where I expected to be—maybe need to adjust a little and I’ve definitely been trending downward the last few years with info published before this ever came out.

And, even with this calculator, I thought (aerocoach?) came to the conclusion that the penalty for being too high is far worse than the penalty for being too low.

That was the Silca blog (and probably Aerocoach somewhere along the way

Right. The key is that this calculator gives optimal pressure for a single set of conditions. If you have some bad pavement, drop the psi. If you want to be more comfortable at a very small penalty, drop the psi. Basically there is no reason to ever go higher than what this calculator tells you to do, and there is often very little reason not to go a bit lower.

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Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
Deals on Wheels - Results, schedule, videos, sponsors

Or me...I've only been saying it on here (ST) periodically for the last 12 years or so ;-)

https://forum.slowtwitch.com/...ost=1744801#p1744801

"On the pressure, from what I've seen, from a Crr standpoint, it's FAR better to "err" on the side of slightly too little pressure than too much. Once you hit the "breakpoint" pressure (where the tire stiffens up so much that too much energy is transmitted through them) the "resistance to forward motion" of the whole bike rises pretty dramatically."

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http://bikeblather.blogspot.com/

When in doubt, if it was a good idea, it was probably Tom A. Good rule to follow.

Indeed, assuming you input the correct information into the calculator ;)

Total system weight... Is this bike plus rider?

Plus nutrition, plus atmospheric pressure, plus the weight of your conscience on race day.

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Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
Deals on Wheels - Results, schedule, videos, sponsors

(I’m assuming)....plus anything else you strap to bike or yourself, including fluids, helmet, shoes, etc.

That's what I thought. Just making sure the rider was included

as Josh mentioned the GP4000s with nominal 23mm actually measure at 29mm.. so probably worth checking, if going to use the calculator..

I like this one,
https://www.garrettwade.com/...ass-calipers-gp.html

inexpensive with a nice retro-grouch look and feel.
Mine used mostly for measuring fishing rod and reel bits and pieces, carpentry etc. Works fine for non-critical applications. If actually engineering the digital ones are better.

your browser or ad-blocker is removing the info.. turn off all adblockers and try again.
or try a browser without protection, like the vanilla Microsoft Edge.

So sorry, the original link was going to the old calculator and not the new one. I've updated all links to go to the proper place.
Please let me know what feedback you have.

https://info.silca.cc/...-pressure-calculator

We also did a video covering a bit of the math/science, data set and other rationale behind the tool.
Would love any and all ST feedback!

---

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Josh

I ran the calculator and did some field testing.

https://strava.app.link/Atot2wpjZ5

Worked great for me!

The worn pavement suggested pressures proved fastest in what was pretty good looking chip seal.

I was blown away by how high the suggested pressures was for me, as I was running significantly lower.

Thanks for sharing a great tool!

the one thing that I think could still be improved in the calculator is the average speed, why not add the numbers not just categories. It has to be linked to real numbers so maybe in parentheses you add the average speed that the calculator uses for those categories. The categories are way too subjective and can really have a significant effect on the result.

I get 25-30psi higher I'm 59kg 68kg with bike... seems EVEN WORSE for lighter riders... if I added 44lbs (20kg) to my weight the difference was 3psi 🙄 this cannot be correct!

Higher than what?
Are you using the actual measured width not the labeled width?

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Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
Deals on Wheels - Results, schedule, videos, sponsors

what he is saying is if he increases his weight by 20 lbs the calculator goes up by only 3 psi for tire pressure... and therefore he does not believe it to be correct.

But the issue is that what ever your assumptions are the increase is correct. Go to Flo bikes and look at their tire pressure matrix, go up 20 lbs and presto 2-3 psi increase... go to the Enve calculation page for pressures the same holds true, increase you weight by 20 lb and the indicated pressure increases by 2-3 psi or so... when 3 different groups indicate the same delta pressure for delta weight, I think you can believe it to be true.

So then the question is why do you believe it should be different than 3 psi per 20 lb increase?

Remember when you increase weight by 20 lb only 10 or so goes to each wheel depending upon front back bias. That is then distributed by the contact patch to the ground.

Anyhow in the end it is true if you increase the total weight the psi pressure per tire should only increase by about 2-3 psi in the moderate weight range eventually it plateaus say between 230 - say 250 lb of weight since you are probably running at the high end of the tire pressure already.

yes, my tires are Mavic Yksion Pro UST 25 tubeless... measure 27 on rim Mavic Ksyrium UST tubeless wheels ..


https://fft.tips/pressure

this calculator take into account impedance as well...

[correction] more like 20psi difference between two calculators and 15 psi difference between 68kg & 88kg

Comparison is to FFT calculator that likewise say they use impedance info...

https://fft.tips/pressure

there is quite a bit of difference between the two calculator... and the seem to depart more and more the lighter the rider...

• me & bike at 88kg result in a +2% difference
• me & bike at 68kg (real) result in +22% Front, +28% difference

I don't know which is more real... I kinda believe the FFT pressures I get... but don't know which is right... could be possible that one model hasn't incorporated enough light riders into their modelling..?


I intend to do a Chung analysis to see which models matches what I find for myself in real world.. raining last two days!


Hopefully tomorrow!

Am I looking in the right place because the Flo Bikes recommendation seem to advise ~15psi difference for a 40lb difference (not 3)??

https://flocycling.com/...ycling-tire-pressure

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Enve site shows a 10psi (not 3) difference between 120lbs and 160lbs

https://www.enve.com/en/tirepressure/

MORE interesting is that Enve, like FFT calculator shows a ~16psi less recommended pressure for 130lb rider (like myself)... 25mm, 18-20 inner diameter (I have 25mm tires, rims 19mm inner [rim width]) —> ~27 on rim.. Enve pressures actually agree with FFT, not Silca 😮!!

hmmm.. someone’s got this very wrong! 🤔

[edit] the Flo chart doesn’t take into account impedance so you can safely ignore that one!

You’ll need to go to any of the individual FLO wheels to see FLO’s tire pressure table - the graphs you linked are not what people are referring to.

Here’s a link to the first wheel in the shop - scroll to the bottom of the page, you’ll see the table.
https://flocycling.com/...o-30-limited-edition

The Silca calculator is based upon a lot of real data that they gathered over years of working with the various teams in various situations. I still feel it is likely more accurate based upon the fact it takes far more into consideration than any of the other tables. However all things should be validated against other data things can go wrong. I look forward to your chung data.

I was drawn to the silca because they popularized the ideas that impedance was as, if not a more important affect than rolling resistance.

https://blog.silca.cc/...stance-and-impedance

Data is data. I don’t understand why data from pros is going to be any more valuable than data from Joe down the street like they are bragging in the video.. sounds a bit like marketing bs to me.

I value this calculator because it takes impedance into consideration (as does the FFT calculator).. looks like ENVE does as well.. FLO’s numbers look like a complete joke.. I would not put any stock in them at all.. mho

What I am wondering is if silca did actually bias their recommendations based on what pro’s actually used vs. what modeling says is optimum? Pros tend to be very conservative and traditional.. if that was part of their modelling, I look at that as a minus, not a plus!

Ok, but like I said previously..
“ the Flo chart doesn’t take into account impedance so you can safely ignore that one! ”

Here is method for doing your own Chung analyses.. all you need is a power meter and Golden Cheetah (free shareware)

https://fitwerx.com/...nd-tunnel-available/

I am not certain that is true or false in regards Flo tables accounting for impedance, what I do know is they are doing a lot of testing in regards to impedance so they are certainly aware and planning on modeling it in future if not already in their tables.

When you model impedance you actually need to take the tire casing into account, it has a significant impact on how inelastic the return is. So there are so many factors that impact the CRR as tire pressure changes. I think Tom A. showed it that when you pass the break point the slope is significantly steeper that the slope prior to the break point. As for pros vs recreational and mid range riders, is the average speed. As you know the FFT and Silca models use that as part of the calculation. Hard to say who is correct though.

I just read their explanation of impedance.. link below... they don't seem to understand impedance.. but it's good that they are exploring it.

https://flocycling.com/...pedance-for-cyclists

The up/down portion of the force vector from wheel impacting a bump, crack or texture in the road does not impact forward motion.. it's the backwards pointing part of the force vector that does.

When your wheel impact an imperfection in the road there is a diagonal force vector pointing from the bump to the centre of the wheel. If you split that vector in two some of it points up pushes the wheel up and over the imperfection.. there is a portion pointing backwards that impedes forward motion and this is the one that causes the "impedance". You can imagine the bigger the imperfection the higher it is off the road, the shallower the angle of the impact and the larger portion of the vector of the impact that points backward and so the greater the impedance of the impact. The more frequent the imperfections, the more impacts per unit time and greater the total impedance per unit time. In the Silca video they mention that smaller diameter wheel will generally have greater impedance and this is because the smaller wheel will have a shallower impact angle for any given bump it hits compared to a larger diameter wheel (26" vs 700c) and so greater impedance.

It is fairly close to my preferred pressure. I typically set mine to 90psi. It calculates 94.5psi rear and 92psi front.

What I want to be able to calculate is what pressure to set it to at 5am in transition to ensure the pressure is correct for the bike leg once the air and bitumen warms up.

I do not personally attest to being all that knowledgeable in the area of bicycle tire impedance, however others who have a greater depth of knowledge indicate there is more to the physics of tire impedance than just force vectors. There is the amount of inelastic rebound in a tire, in what I understand (though I can stand to be corrected) is related to the amount of energy that is returned after the compression and rebound phase of a bump. So therefore the CRR of a tire with a stiff casing is much higher than a tire with a supple casing. Tom Anhalt has explored a lot of tires and has a spreadsheet of relative CRR for different tires : https://docs.google.com/.../edit#gid=1567734751
the work that Flo are doing is seeing if they can determine the CRR break point relative to tire pressure using a vibration sensor. They are producing some interesting results. Again I claim no expertise, just viewing the data and seeing how things are converging to a common result. So I think in general we agree that tire pressure has an impact on CRR. Also CRR seems to be important to riding efficiency meaning for the same input power you get more output speed. Whether any of these spreadsheets are giving true values of CRR or optimal tire pressure is an interesting question. This a relatively young area of exploration so it may take some time to reach consensus.

The hysteresis effect you describe is mitigated by more supple tires and affects "rolling resistance"... which is really just the more the tire casing gets squished, bends the more energy is lost mostly to heat and sound to the environment... so you can imagine that the more pressure less squishing.. less energy loss..

Impedance is a different phenomena.. its basically the loss of forward motion from the impacting imperfections in the road that add together to effectively push the bike backwards.. almost like wind.. so the softer the tire the more the tire squishes and is not affected by this effect...

The thing is that both these effects are impacting the bike at the same time and are oppositely affected by tire pressure... the "breakpoint" is the pressure where you add these two factors together and the add to have the lowest negative affect on forward motion of the bike (not really Crr, since impedance really doesn't affect rolling directly... not sure?).

but, yes if you have a more supple tires (with less "rolling resistance") means squishing the tire to avoid "impedance" results in less energy loss total.. as well just the squishing as a result of creating necessary contact patch is less as well.. so both rolling resistance and effective impedance will go down.. but the point is they are not the same thing.



Slica blog actually has good explanation I've added few images below.. this is why smooth drum analysis (higher pressure is better) lead to wrong real world pressure recommendations.. and it NOT about comfort... you will go faster at breakpoint pressure... this is about performance!

I found a good way to grasp impedance is this...

Imagine you put a broom stick on the ground... then ride up to it VERY slowly.. you can ride so slow that when you hit the broomstick it stops your forward motion.. if you've taken any physics at all you'll know that in order to stop you, it needed to push back on you and bike with an equal and opposite force. You can ride faster and you will make it over the broom stick, because your momentum overwhelms that force, but as you go over it you are still being pushed back by that force and it will slow you down a little bit. Now imagine hundreds of broom sticks in front of you every few inches, each injecting a small impulse that will add to make it harder to ride.. this is impedance.. shrink it down to the size of cracks, bumps and even the texture in the road.. same effect though.

Making the tire soft and squish more allows you to roll over and not be affected by impedance, BUT making the tires soft and squish more even when the bumps are really small and have little affect makes the tires lose more energy in form of heat to the environment... so it's a balancing act... the lowest TOTAL losses are at the "breakpoint".

Impedance = resistance to forward motion from repeated impacting imperfections in the road that push bike backwards
Rolling resistance = energy losses from squishing tire

Silca made up the word Impedance since it's not strictly rolling resistance so needed to distinguish it...

So here are my Chung analysis result... this was my first crack at this and likely was a little too windy, so the data was a bit noisy so YMMV.. might try again... probably the most significant finding is that the difference appear to be TINY except for the FFT "hard packed gravel" recommendation.. this was also on super smooth pavement... much smoother than I typically ride on, but a half pipe type parcour as required.. going to find a more typical, bumpier parcour to get more relevant result for myself in my next try..

The thing about tire pressures is there won't be much of a drop off until you go over the ideal pressure. If the pavement is great like you stated, then those pressures are likely way under recommended, which would mean they're all going to be relatively close based on the slope of the curve before and after the point of impedence.

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Good point!

And looking at the curves (seemingly confirmed by my little test) the smoother the pavement the wider the band where changing pressure has VERY little effect.. so you pay little penalty for going for comfort, grip etc.. within limits of course.. also given this, it’s probably best to pick your pressure based on the WORST roads you will encounter... interesting 🤔

Different ways of looking at the same thing.

When a bump in the road pushes against the bike with a backwards-and-upwards force, that "backwards and upwards force" can be described as slowing the bike due to its backwards component. But visualize it in terms of where the energy is going: it can also be described as converting the bike's forward motion into vertical motion.

I like the latter description better when trying to describe the phenomenon, because most folks don't really know how to visualize force diagrams, whereas a squishier tire producing less vertical deflection in the bike+rider when it rolls over bumpiness can be fairly intuitive without much physics knowledge.

But the vertical force vector has zero effect on the forward motion/energy.. only the horizontal portion of the vector does... force needs to be in same plane to add or minus the forces.. if you rolled over smooth bumps (like a rollercoaster) you would not lose that energy.. would just go between kinetic and potential then returned as kinetic.. like bouncing on a spring.. no loss in energy though.. when you impact a road imperfection.. kinetic energy from you and your bike is lost to the environment though... heat, sound from force of each little impact in the opposite direction of motion...

I think there is one aspect that maybe we both did not have 100% correct but is noted in the Silca article on impedance. CRR is made of 2 components, one is casing losses (hysteresis) and the other impedance. The first part of the CRR curve is mostly hysteresis casing losses and declines as you add more air pressure, then as a certain point the impedance effect overwhelms the effect of hysteresis in the opposite direction and becomes the dominant portion of the CRR. So how I understand this is as the casing becomes more rigid there comes a point where the tire does not deform adequately over an imperfection and suddenly due to this the force vector points backwards (probably an over statement but you get my idea) up until that time the force vector was mostly upwards because the tire could deform adequately to overcome the imperfection. This, in my way of seeing things, is why a supple tire have a lower CRR and vice versa for a stiff tire casing. It also shows that the impedance effect gets rapidly worse because of the stiffening of the tire due to tire pressure.

So below the break point CRR is mostly caused by tire deformation losses (what I believe is called hysteresis). Above the breakpoint pressure the dominant effect is impedance. The impedance effect is much stronger for changes in pressure above the break point as shown by the slope of that portion of the curve. That is why the vibration concept that Flo is pursuing makes sense. Up to the break point the vibration is absorbed by the casing of the tire, but once the tire reaches the break point the tire gets more rigid and the vibration is not as well absorbed but is transmitted through the system. They have been able to show this already with the data they have presented. It will be interesting to see what they learn using this approach.

I think this is early days in this study and there will be new items added but it is interesting that Silca and FFT do not add a tire quality aspect to their pressure calculator. Based upon this it seems that tire volume is more important that casing quality?

Yeah... I can see the vibration thing working.. depends on how implemented but, I can see it..

Can see cases where

1. the tire is soft enough to totally absorb all the force from impact, deforms and then returns energy as expands with some small losses from hysteresis (essentially heat) = no vibration
2. the tire is completely rigid and system absorbs all the force = STRONG vibration
3. all ratios in between.. where amount some amount is absorbed and returns with hysteresis losses.. but some force of impact make it through to system = magnitude of vibration dependant on how much tire absorbs based mostly on the pressure

But I think the above system could tell you how well the tire is doing at absorbing the bumps... but wouldn't let you know how well it was doing with hysteresis.. so this would isolate for impedance, but not account for rolling resistance.. so how much energy is lost in heat from bending the tire carcass..


FFT actually does let you enter the Crr for the tire which you could get at e.g. https://www.bicyclerollingresistance.com

The circumstances in which the horizontal component exists are relevant. If you're riding steady and straight along a flat road, and the force from the road onto the wheel is only ever pointing perfectly straight up, it means that you're on a perfectly-smooth road surface and you won't ever be bouncing at all.

When you hit a bump, the thing that causes the rearward-oriented force component is the same thing that causes the vertical component of the force to exceed gravity and cause the bike and rider to accelerate upwards. You can isolate them in a force diagram if you want to, but they're not really separate physical phenomena. Again: visualize the situation in terms of the energy. If you don't think that the energy that bounces the bicycle and rider with overly-stiff tires on rough roads is coming out of the forward motion, where is it coming from?


The rollercoaster example is actually a really good way to visualize what I'm talking about.

If you're rolling up a steep slope, the force from the rails onto the car has a strong horizontal component, and forward motion is being converted to vertical motion very rapidly.
If you're rolling up a shallow slope, the force from the rails onto the car is only weakly horizontal, and forward motion is being converted to vertical motion only very slowly.

The reason that you regain the forward motion lost to vertical motion in the rollercoaster case, but not for the bump in the road, is that the rollercoaster rolls back down a second smooth slope later.
What if the rollercoaster doesn't do this? Imagine a rollercoaster than rolls up a 1-foot rise, and then simply flies off the rails onto a set of unsloped rails that's one foot lower down. When it lands, obviously there will be a jarring impact, and anyone in the cart will suffer a painful experience. But you won't get any speed back: the energy that was used to go uphill has now been wasted, dissipated through mechanical friction by rattling the cart and the riders' bodies, and in the form of a loud sound as the cart hits the lower rail.


Some friction obviously happens all throughout the process. But friction requires relative movement in order to happen, and a lot of the energy that gets "lost to heat" is initially converted to vertical deflection of the bicycle and rider. How do you dissipate energy as heat in the rider's body? Shaking the rider up and down is one way to do it! From a raw performance standpoint, the relevant issue is that the energy doesn't have a good way to get converted back into forward motion.

Update... response from Silca

Seems FFT calculator does not do an real impedance modelling... except in a very rudimentary, implicit, approximate kinda way.. assume that a % drop... mm drop in tire from load with given weight has x amount of absorption.. also not incorporating real world data to feed the modelling...


SILCA velo "We are the only calculator that I am aware of that uses calculated impedance values.. so what you have here is the result of thousands of actual field test calculations to find peak minimal rolling resistance, and we then fit an algorithm to that to help interpolate the empty spaces.. so for example, we have more than 120 optimizations across 5 teams, 30 athletes and 4 tire sizes all done in the Carrefour de l'arbre.. so we then curve fit for 26mm tires, riders 165-210lbs system weight.. then we fit for 28mm tire data, then for 30mm tire data and so on. Each of these tests originally having the result of being the actual pressure used by that athlete on that day. Our data comprise more than 20 pro triathletes across 4 years ad 5 tire widths on the Queen K at Ironman and so on.. from that, we've built the algorithm to predict the likely peak minimum rolling resistance likely for your weight, tire size and surface. All other calculators that I know of use either % drop of tire on a flat surface for a given load OR height of drop on a flat surface for a given load. Both of these methods are good starting points to begin the optimization process, but are only indicative of static tire stiffness on a flat surface and have nothing to do with impedance or any of these other factors that prove out to be critical in the real world. Also important to note that most calculators by manufacturers are also constraining their data by the max pressure of the rim or tire being sold.. so many of them will take %drop and then just shift the results or limit the results based on these stated pressure limits.
I love your idea on % of surface per ride, we use this in our pro team optimizations and do plan to include it at some point in a future version of this calculator.
As for tire type, this has proven not to affect pressure in real world testing. Since the pressure is controlling the spring rate and the tire construction is controlling the hysteresis this makes sense, think of tire pressure as being the spring in your suspension and the tire construction as being the damper.. across small changes in damping, the optimal spring rate remains unchanged."


SILCA velo "This is because our minds tend to approach all problems as being linear.. so a 25% change in system mass should result in ~25% change in pressure. However, the tire stiffness and spring rate behavior is non-linear to tire size and is also non-linear to bump input performance...and also remember that the calculator is trying to find the optimal middle ground between impedance which is non linear AND casing losses which are also non-linear. This is definitely an area where the mathematical model has not caught up to the field testing work that has been done, so we aren't yet in the best spot to have tested a hypothesis detailing the specifics, but I can tell you that nothing about any of it is linear. This could also be a place where having the entirety of the data set based on pro athletes could skew the data.. they are all much lower body fat and higher muscle % than the rest of us which theoretically lowers impedance which would also theoretically increase the impedance pressure break point.. but again, this is the data set that we have."

SILCA velo "So this FastFitnessTips calculator is combining % drop and mm of drop data and does not have any functionality to predict impedance. This is the type of calculator that we used years ago to find a starting point to begin optimization and our calculator is based on the results of all those optimizations."

what you are not consider is that.. if you use energy to raise something up against gravity.. when it goes back down, gravity restores all of that energy you put into it.. there are no losses from vertical up and down...

If exert energy to ride up a hill against gravity... when I roll down the hill, I get all that energy back when I roll down the hill.

I addressed this in my post.

Moving downward through a gravitational field returns gravitational potential energy to kinetic energy. But it only usefully gets converted back to forward movement if you do something (such as smoothly roll down a slope) that redirects it to forward movement.
That's why I gave the example of a roller coaster cart that simply flies off of a drop and then lands on a flat section of rail below. The cart will accelerate as it falls, but it's only accelerating downward, not forward. And when it lands on the lower rail, its downward motion gets dissipated in an impact rather than becoming forward movement.
The same happens to a bicycle that pings off of a small surface bump. When the bike+rider get sent upwards, there's no mechanism for that motion to get converted back into forward motion later: it ultimately gets dissipated as sound or converted to heat from frictions within the rider's body and the bicycle.

It's actually not so much what you imply above...it's more about whether or not the energy used to compress the leading half of the contact patch is returned in the trailing half, or not. If that energy gets "through" the tire and is dissipated as vibrational losses in the rider, then the "impedance" losses increase.

I wrote this article back in 2007 about the source of rolling resistance: https://www.slowtwitch.com/...ling_events_226.html

This article was written back in 2009 about "impedance" effects with pressure: https://www.slowtwitch.com/...in_a_tube__1034.html

Both would be good to review for this discussion :-)

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http://bikeblather.blogspot.com/

HTupolev.. you are correct that the vector is diagonal and some force directed up and some back... this why to understand which forces normally one would split that diagonal vector into one facing straight up.. that you don't need to consider because that portion of the force just going to be returned as the bike goes back down and as the tire returns from being deformed... AND one facing backwards...


I drew diagram below a while ago to try to understand how/why a smaller wheel would be more affected by a given obstacle of a given size.. tend to roll slower as Silica velo mentioned in their video..


First you draw vectors from example a pebble through the centre of the wheel.. the length of the vector is measure of magnitude, so they are all the same length (same weight rider and bike riding at same speed)..


you'll see that the magnitude of the backward facing vector is larger and larger the smaller the wheel compared to the obstacle as observed in real life... ever hit a pebble with a shopping cart? LOL... can imagine if the obstacle was the same size as the wheel (brick wall) ALL of the force would be directed straight back..
[inline Wheelsize&ForceVectors.png]

Nice.. predates Silca blog entry by decade 😎

I do like the example of.. put a broom stick down.. roll up to it up to it very slowly.. it stops you moving forward.. why? because it exerts a force on the bike in the opposite direction of your travel pushing you backwards! That is impedance.

Immediately understandable by just about anyone.

Right, but if you just roll over it, the tire "pushes back" on the other side of the stick by nearly the same amount, pushing the bike forward...and the road roughnesses we're talking about are orders of magnitude smaller than a broom stick diameter. Rolling up to a broom stick is only doing ~half of the action of rolling over a "protuberance".

If you read the Silca blog carefully, you'll see that Josh mentions me ;-)

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http://bikeblather.blogspot.com/

When we're talking about an over-pumped tire going over road irregularities, it isn't well-returned, because the contact patch isn't doing a good job of rolling down the far side of each irregularity. If it did, the backwards-pointing component of the force wouldn't matter either, because it would have a reciprocal forwards-pointing force on the far side of the bump and you'd just gain all of your speed back on the far side of the bump.

Back to your original point: "I get 25-30psi higher I'm 59kg 68kg with bike... seems EVEN WORSE for lighter riders... if I added 44lbs (20kg) to my weight the difference was 3psi 🙄 this cannot be correct!"

As noted at a very early stage of this discussion Silca has input more data into their calculation than the other calculators and why I tend to believe it to be quite accurate. I also assumed that tire casing did not have a big impact or they would have added this to the calculation, but the quote from Silica Velo is a good way to understand it. So over all they are trying to optimize tire pressure for performance and the changes are not huge for changes in system weight. That seems to mean that back to your original question why if you increase the system weight by 40 kg does the tire pressure only go up a few psi? it would seem that the increase in spring rate is non linear. So yes they got it right and FFT is not correct for the reasons pointed out. Yeah Silca!!!

The only things I would like changes are the type of road and proportion of road and more the actual speed ranges instead of a vague word description such as "moderate group ride) is that 27-30 kph or 30-35 kph????? where does the speed change? even then the changes are small ie recreational to moderate group ride may be 1 psi or less depending on proportion front to rear weight distribution.

In the end I know they put a lot of time, data from real word trials, and calculations into the calculator and I have no reason to doubt it. Josh has done this stuff for a lot of real world situations where it counts to be right. Based upon the fact he is still in high demand and I do believe he is a very smart guy, I am leaning towards believing what he says is likely fairly reasonably correct. Now I need to read Tom's (thanks for the links TA) articles and educate myself on impedance and hysteresis. This thread has been a good place to learn a bit more. Thanks to the expert inputs.

This made me doubt the numbers.. but not really my concern... I really just, selfishly want to know what my numbers should be 😀 I am coming over to the dark side.. a little bit.. and having less doubts 😀

Most significant thing I think I've learned - I though @realbdeal had a really good point, when he pointed out that... if you look at the graphs (it's there but it didn't really register for me).. and the little field test I did showed it too.. that the smoother the road the flatter the effective Crr to rec. pressure curve before the breakpoint.. where there is a band of pressures that almost give the same Crr.. so from a real world practical perspective it's really if you're in this ballpark, within this band, you're good and there is really no performance penalty for a little above or below a precise optimal breakpoint pressure.. this is why I think in some way could show this that would be awesome... if you can drop the pressure 15psi (as shown in my field test) and be WAY more comfortable and that results in a 0.5W difference or no difference at all.. that would be good to know.. I would go for the 0.5W increase for the comfort gained by a 15psi drop in pressure... so if they can spit out the optimal then allow you to drift away from that and see what that means in terms of W or speed decrease that would be awesome from a practical, use experience point of view... of if they could just show the curve based on the things you've entered, then you could hover over the points of curve either side of breakpoint that would work for this use case...

[edit...I did also suggest a multi surface feature.. so could enter 50% smooth, 25% chip and seal, 25% goat track.. lol.. said they do that for clients and were thinking of adding to calculators...]

welcome to the Dark Side... LOL Josh actually has a Darth Vader sticker on his computer on the video about the calculator...I agree it would be wonderful if they did an interactive graph, that would be awesome. I agree with you knowing where you are on the graph would help make a rational decision, like you said, less pressure, slight wattage loss, and increased comfort, as well they could indicate the danger zone for wheel damage/ pinch flats, this would be ideal.

I did notice the mention when I looked back yesterday...

Hmmm.. but I would think that any bumps of the size that a tire can completely deform around are taken care of, really by rolling resistance and the losses are from hysteresis loses.. just ones that are not accounted for in smooth drum because the tire carcass will do more bending around all the cracks, smaller bumps and texture etc than accounted for on a smooth drum... but for everything that is only partially taken care of by tire deformation, there will ALSO be a collision that takes place and that collision will push that bike back... if the tire was completely deforming around the obstacle would you feel the collision? So some of the force is making past the tire and into the bike.. so we know that, that portion is not going to be returned when the tire recovers from deformation.. correct?

Yep...any energy making it past the tire is going to be mostly absorbed and not returned.

Here's the thing about roller testing...it's a GREAT way of determining the hysteresis losses from deformation and ranking tires. If you add in additional "roughness" to the test setup that increases the deformations, it's just adding additional hysteresis losses in a proportional manner, and the rankings don't change. This is why I'm not a fan of adding "roughness" to a roller test. It doesn't add any additional information.

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http://bikeblather.blogspot.com/

Yup.. the rankings don't change.. but as you say the magnitude of the wattage changes.. you obviously have more experience with this than me, so I assume this to be generally true, is strictly true in your experience..?

Interestingly, I noticed that generally tire rankings don't change with pressure... BUT, some actually do.. some tires change their ranking based on tire pressure...

https://www.bicyclerollingresistance.com/...reviews?orderby=rr60

so wonder, could there be tire characteristics that allow it to isolate the bike better or worse from road.. and that don't vary proportionally with the its hysteresis characteristics...?

Wondering if you could create a rig where you quantify the hysteresis losses on a textured drum... but also quantify the isolation characteristics and therefore the non-hysteresis losses of the tire with an accelerometer and/or strain gage attached to the wheel itself.. then have maybe 4 standard textured drums that you could use to test.. then get a better TOTAL picture of how a tire is actually going to roll.. what pressure a tire rolls best at on given terrain etc..?

Interestingly it seems even the shape and size of the obstacle seems to impact the forces in non-tribal ways.. maybe even using a drum, through practical, might not realistically mimic real world closely enough for this type of testing.. maybe the on bike, black box type testing where you just look at input and output is best..? [..too many moving pieces..?]

https://blog.silca.cc/...r-is-stiffer/harsher

But, there has gotta be a better way of testing tires... what is done now is really inadequate and we know only captures about half of the story.. as some people were talking about for a decade already 😉

I'd be careful about drawing any conclusions based on values from over such a wide pressure range (especially considering the magnitude of differences shown, i.e. tenths of watts). Although that wide range might be interesting...I find it useful to compare the tires in a pressure range they'd most likely be used for the majority of riders.



That "characteristic" you're talking about is the air spring "stiffness", AKA "pressure"...so, if you need better isolation, choose a wider tire so you can lower the pressure.



I think you might be over-thinking it ;-)

The way tires are tested now IS pretty good...it's just that too many people don't have the insight to understand how it relates to "real world" conditions...and they keep trying to add in surface roughness, etc. to the testing.

It's actually pretty simple. Smooth roller testing give you an idea of the hysteresis performance on hard surfaces (smooth or rough). With field testing, one can then also find out where the "breakpoint pressure" of the system is...and then just make sure you stay far enough away from that for the given speed, surface, and load.

Now then, if you want to talk about how tires perform on dirt...that's a whole 'nuther ballgame...but, not impossible :-)

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http://bikeblather.blogspot.com/

Weird... never heard that before 😉

So I've tried my hand at a Chung analysis... was fairly painless and I was already a user of Golden Cheetah for my performance management software and it's just included in there as one of the tools.

What would you suggest as a user friendly method for finding breakpoint?

The way I found it originally...VE ("Chung") analysis at different pressures.

But, THE most user friendly method would be to just use the Silca pressure calculator ;-)

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http://bikeblather.blogspot.com/

Makes sense.. thanks so much for your input, it's been quite educative,

...and thanks for "overthinking" this 😉 we wouldn't have our current understanding without people like yourself tinkering around with this stuff and the out of the box thinking 🍻

Just came across this thing, figured I'd try it out and see what I was doing wrong.

Interestingly, it spit out almost exactly the same pressure that I'm using now. I've been using 100psi on nominal 23mm, 24mm actual width. calculator says 100.5 psi front, 103 psi rear.

Also, I wanted to see what it came up with for my race wheels, if we ever get back to racing. 21mm width (nominal and actual). If I pick Cat 1/2/3 racing - I'm up to a whopping 125/128 at my current weight (triggered the pinch flat warning, but not an issue for tubulars).

I really should get wider tubulars, but these are NOS, never even been glued yet. given that they are tubulars, I could run a bit lower pressure than that, probably 110-115???

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Oh man, I've been driving an RV across the country for a friend for the last 3 days and totally missed this tire pressure party!!

For s5100e.. the calculator does have a pinch flat predictor.. this is run by an energy equation that take tire spring rate and radial height and then compares compression energy to rider mass/velocity. Early versions of the calculator had an 'average speed' entered as a velocity number, but since the energy calculation is taking 'average' velocity and then assuming a velocity distribution based on that number, people were always tripping the warning by saying they rode at 'average speed' of 25mph..

As for the rest of it, the problem with impedance is that it really encompasses 3 components, 2 rider related and 1 tire related:
1. High vertical accelerations make for extra high Crr numbers, so to Tom's broomstick analogy, normal Crr is the difference between energy put into the tire to make the contact patch vs energy given back by the tire as it returns to shape. But in the impedance realm, the vertical forces can be so high that the tire is off the ground when it gives back that energy..so if you high speed a tire hitting a broom stick, you see this massive compression against the tire both vertically and diagonally against the direction of motion, followed by the tire going 'airborne' over the other side of the broomstick and the tire regaining shape before hitting the ground.. so NONE of the energy is going back.
2. Rider contact points: different riders will have different contact point hysteresis and different stiffnesses of bike will affect this as well. Ride the Carrefour de l'Arbre 1 time and your hands will be hot and blistered.. this is hysteresis
3. Rider body composition hysteresis. This is perhaps the biggest question using our data.. nearly all of our data comes from world class athletes and even the non pros on our list are guys/gals with some serious fitness and palmares. This is important if you think about hysteresis as damping.. the more fit you are the lower your body damping coefficient will be. To a 180lb person who is 2% body fat will have lower damping than a 180lb person who is 20% body fat, so in theory this should likely move the break point lower for higher hysteresis people and higher for lower hysteresis people... and looking at the athletes on our list, they are by and large about the lowest hysteresis people you could find!!

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I wonder about that. If we're talking about something as high-frequency as paved road irregularities, is the rider's body actually a responsive enough part of the system that rebounded energy would be meaningfully biased toward returning as forward motion? I wouldn't be surprised if a lower-hysteresis body just means that the energy bounces around longer before being dissipated.

Hi Josh, thank you for chiming in. The whole discussion of body composition and contact point hysteresis is very cool latter probably ripe fit innovation to mitigate!

Wondering about the case with the broomstick. In the case where the wheel hits the broomstick, tire doesn’t fully compress and the bike is lifted up & over the stick (launched in air or not). When the wheel hits the broomstick there is a diagonal vector at the point of contact the vertical component of that diagonal vector is the force available for lifting the bike up and over... but there is a horizontal component to that vector pointing straight backwards, opposing forward motion. This will impart an Impulse (F.dt) on the bike.. basically bike and earth exchange some momentum and bike slows down..

a) is there something wrong with this thinking?
b) do you account for this type of “collision” type of interaction in your impedance thinking, modelling?

Hi Josh, I am not certain why when I pull the SPPC up I no longer see the pinch flat side bar when I enter the pro version. As for speed I was referring to a speed range or average, not an absolute number assuming a fast group ride is a range depending upon what is fast???? my fast is not real fast and so it is a bit hard to relate those numbers. So what I mean is have both the text as well as the intended speed range. But i note that say between recreational and fast group is only 1.5 psi front and 1 psi rear so if I assume the slower then I am still on the correct side of the breakpoint.

For the Rider hysteresis maybe add in BMI? ;-)

Thanks for the calculator I swear by it even though I am not certain I interpret it all correctly I typically look at what the result is an how sensitive it is to the areas I am uncertain in.

Did some more testing this weekend on more typical road surface and wider range of pressures... not lining up with Silca calculator at all actually.. actually getting that 20-25psi diff... want to do that do one more set of testing.. just to make sure...

found some more advice on crunching data here:
http://www.floataero.com/...esting-scenarios.pdf

Got a bit busy...

Three trial... getting better at doing these I think...

I have gone back to thinking the Silca calculator reads high 15-20psi for riders of my weight ~60kg/72kg (bike+rider)

Some of my observations/conclustion:

1. on very smooth pavement ~80ish psi tested lowest Crr, but the difference in Watts between 60-80 was less that a Watt.. imho 60psi would be the better practical choice given 1) comfort & fatigue 2) likelihood of mixed road texture over totality of ride meaning that over the ride a lower pressure would be better performing 3) almost no performance penalty for going to lower pressure... ~80psi is what silca recommends
2. on textured pavement with some cracks 60psi (vs ~80ish psi to 73psi as predicted by Silca calculator) seemed to be the better choice over two trials..
3. I observed a bowl shaped curve, but did not observe the steep, marked impedance increase as seen in other's analysis.. still improving my process at getting better data.. so work in progress... I have pretty low BMI so could some of this effect be much lower for me??

Imagine you must have been in loop for this since they quote your work and Josh's work quite a bit... tested on textured drums to simulate cobbles... BUT also add a shock absorber to simulate body hysteresis... the "over thinking" test I was suggesting.. does seem to add imho significant additional info 🤔

Super interesting that

1. breakpoint is not just a matter of road roughness, tire width and rider weight.. but also seems to be an inherent characteristic of the tire itself and it's construction as well.. all thing being equal different tires constructions will have different breakpoints!
2. As expected, wider tire will have a lower breakpoint pressure, but (as I expected) will have a lower power number at it's break point pressure as well..

Main article link below... need a membership to see the actual testing results...

https://www.velonews.com/...ols-when-testing-it/

I was only asked to review and comment on the article AFTER all of the testing was done (as was Josh).

That said, one thing that probably didn't make it into the article which Josh had pointed out, is that although the Wheel Energy test rig does have a bit of damping inherent in the load application (due to the use of an air cylinder), the amount of damping supplied is basically an order of magnitude lower than what would represent the damping of a human body. This will have a pretty large effect on the absolute breakpoint pressure for a given roughness, load, and speed.

So, although they appear to have found a breakpoint pressure with the rig, that still doesn't really give any actionable information...

I expressed my opinion about the necessity of "rough surface" testing at the time as well...but, I'm pretty sure the VN folks are of the opinion that it's hard to convince people without having something like this, for many of the same reasons I pointed out a year ago (i.e. lack of understanding of the loss properties of tires by the consumer).

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Oh... ok..

I had the same suspicions as you state here..

1. does that air cylinder REALLY add hysteresis in remotely same range as a human body? thought, not likely, but didn't really have details on that.
2. The values surfaced really don't have any absolute value anyone should take and use to set up their actual tire pressure.. that those breakpoint pressures likely can't be taken at face values..

BUT... that being said... what I found it interesting is that it does let us do something that's hard to do otherwise.. set all variables constant and see if tire construction itself has inherent characteristics that can affect break point pressure and this testing would seem to indicate... YES, it does... and seems that it's NOT necessarily correlated directly with crr.

So it's not just a matter of rider weight, tire size, surface roughness... seems the specific tire construction also matter in picking optimal tire pressure.. that is something new... no? Not sure they recognizes that as something new in the article.. wasn't highlighted, but a question I was asking earlier and seems we have at least a preliminary answer.. and I think the popular assumption was that the tire construction didn't matter WAS just directly correlated with crr.. but this testing would seem to indicate that is not be the case.

Right...but are you trying to find the tire with the best Crr, or looking for which has the highest (or lowest) breakpoint pressure?

In other words, let's say you have 2 tires and one is 1W per tire faster, but the other has a breakpoint pressure 5 psi higher (even though BOTH breakpoint pressures are most likely well above typical pressures you'd run on surfaces where breakpoint is a factor)?

I don't know about you, but I'd still pick the one with the lower Crr...

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http://bikeblather.blogspot.com/

Hmm. How accurate are the pump gauges?

I would of course pick the tire with the lowest crr...

BUT then to get the best performance out of those tires I want to know what pressure to pump them up to... the initial subject of this thread actually! ...having the knowledge that the breakpoint pressure and optimal tire pressure is not a function of crr, not a function of tire size means using those criteria to guide you could lead to wrong answer on optimal tire pressure.. and that's good to know!

example the Silca tire pressure calculator does not take tire construction into account (understand would not be reasonable to do that) so this could lead to inconsistent, error prone results.. correct?

So reveals an inconvenient truth... takes us back a few steps in terms of convenience unfortunately... that the only accurate way to determine optimal tire pressure is field study.. with the specific tires you want to use.

Just remember that the Silca calculator isn't giving you the breakpoint pressure...just giving you the overall best pressure for your inputs, which I'm fairly certain is going to be quite a bit under any breakpoint pressure for those same conditions, because: " 'Tis far better to err on the side of too little, rather than too much, pressure" ;-)

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http://bikeblather.blogspot.com/

True enough... after doing some of my own field test I've found that Josh's advice that he gave as a guest on a YouTube channel was the best technique I have found to find optimal pressure... paraphrasing... 'go as low as it takes so ride feels "smooth".. then go up if it handling feels wonky'

But as a bit of a biking science wonk... I find this finding in this testing really cool...

Found link (@10:44)