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!

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