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What calculator to find the correct tire pressure?
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I understand tire pressure is very important for rolling resistance and aerodynamics. To ensure that I have the correct pressure I bought a Blackburn Honest Pressure Gauge (https://www.blackburndesign.com/...-pressure-gauge.html) with a claimed accuracy of 1%.

But how do you know what pressure is "correct"? I have tried the CyclingApps Exact Tire Pressure and TyreWiz, but believe the first is better since you can adjust for dry/wet, tarmac quality and balance. What do you use to decide the optimal pressure?

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Re: What calculator to find the correct tire pressure? [Allanhov] [ In reply to ]
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Silca has a lot of interesting info on tire pressure, starting here (see page 5 too): https://blog.silca.cc/page/4
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Re: What calculator to find the correct tire pressure? [Allanhov] [ In reply to ]
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What tires are you using?

How much do you weigh?
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Re: What calculator to find the correct tire pressure? [jimatbeyond] [ In reply to ]
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jimatbeyond wrote:
What tires are you using?

How much do you weigh?

Have Schwalbe Pro One tubeless 25mm with measured width 26mm on the front wheel and 28mm on the back. Consider trying the GP5000.

Weight 68 + 10kg and have 50/50 weight distribution front/rear wheel

3 x Norseman winner - http://www.triallan.com
Ambassador of:
Quintana Roo - https://quintanarootri.com
Morf-Tech - http://www.morf-tech.com
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Re: What calculator to find the correct tire pressure? [STJ_2028] [ In reply to ]
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STJ_2028 wrote:
Silca has a lot of interesting info on tire pressure, starting here (see page 5 too): https://blog.silca.cc/page/4

Thanks. I have it on my reading list and enjoyed the Flo Cycling podcast with Silca owner about the subject. Looking forward to part 2, because it left me with more questions than answers 😂

3 x Norseman winner - http://www.triallan.com
Ambassador of:
Quintana Roo - https://quintanarootri.com
Morf-Tech - http://www.morf-tech.com
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Re: What calculator to find the correct tire pressure? [Allanhov] [ In reply to ]
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What strikes me most about this sort of discussion is the type of graph you often see. Rolling resistance vs Tire pressure. Initially the resistance goes down as pressure increases. Then there is a break point and it goes up. So it doesn't seem unreasonable to look for that break point and get the least rolling resistance.

But when you look at the shape of the graph it curves gradually into the break point then sharply away from it, as pressure increases. In other words there are diminishing returns as you get close and then a more significant penalty when you go over the break point.

I agree there is some good info on the Silca site. For instance part-4b-rolling-resistance-and-impedance has the type of graph I'm talking about. There is also a chart that puts the above/below break point thing into example figures. In their example there is 1 watt penalty for being 10 psi under the break point but a 6 or 9 watt penalty for being 10 psi over (depending on the surface).

I don't know what sort of surfaces you are racing on. In the UK a triathlon, in my experience, is often on not great roads. In the worse case I wouldn't get a chance to ride the bike route before hand and it will be on a lot of different roads and therefore surface. So what surface would someone plug into a calculator to get the recommended PSI? You'd have to use the worst surface that is a significant distance.

Given all this my take away is not to sweat it.

Your tire will have a min/max pressure. They make the thing and come up with those numbers for a reason. If you pump your tires to the min figure then you will be the better side of the breakpoint. My reasoning is that only using the resources of something like Team Sky would someone have an accurate breakpoint figure and what will they get? 1,2 maybe 3 watts on me?

The counter point to that is if you do get a chance to ride the course beforehand with time to experiment then I think you can feel the break point through test riding and gradually pumping the tires up. But that's another conversation but I'd rather do that than type in guesstimated variables to a calculator.

TLDR relax, take a safe low guess and it'll be fine.
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Re: What calculator to find the correct tire pressure? [OddSlug] [ In reply to ]
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This was much the point of Josh’s asymmetry discussion in his last podcast. Still, there needs to be some sort of calculator about this stuff.
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Re: What calculator to find the correct tire pressure? [iamuwere] [ In reply to ]
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iamuwere wrote:
This was much the point of Josh’s asymmetry discussion in his last podcast. Still, there needs to be some sort of calculator about this stuff.


I've long said (basically ever since identifying the "breakpoint" in my first Crr vs pressure VE runs)..." 'Tis far better to err on the side of too little pressure than too much." ;-)

As far as a calculator of some sort goes...I used to think having something like that would be cool...but now, I'm not so sure. After all, there's way too many variables to get a true "optimized pressure", or even a range...at which point you're back at using the generalized guidelines as a starting point and going from there with experimentation.

For road or mixed surface use, I'd start with the Berto curves (based on measured tire widths and wheel loads) and go from there.

Edit: IME, the Berto calcs cause the front tire to be significantly under inflated. After all, the load on the front tire increases quite a bit from the static load during braking and cornering.

I usually figure out the rear load, and then drop the front pressure by 5-10% based on the bike setup.



http://bikeblather.blogspot.com/
Last edited by: Tom A.: Feb 17, 19 17:42
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Re: What calculator to find the correct tire pressure? [Allanhov] [ In reply to ]
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Allanhov wrote:
I understand tire pressure is very important for rolling resistance and aerodynamics. To ensure that I have the correct pressure I bought a Blackburn Honest Pressure Gauge (https://www.blackburndesign.com/...-pressure-gauge.html) with a claimed accuracy of 1%.

But how do you know what pressure is "correct"? I have tried the CyclingApps Exact Tire Pressure and TyreWiz, but believe the first is better since you can adjust for dry/wet, tarmac quality and balance. What do you use to decide the optimal pressure?

If you have an iPhone, the Mavic app seems to do a good job. Not sure if there's an equivalent for Android or general web browsers.
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Re: What calculator to find the correct tire pressure? [sathomasga] [ In reply to ]
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sathomasga wrote:
Allanhov wrote:
I understand tire pressure is very important for rolling resistance and aerodynamics. To ensure that I have the correct pressure I bought a Blackburn Honest Pressure Gauge (https://www.blackburndesign.com/...-pressure-gauge.html) with a claimed accuracy of 1%.

But how do you know what pressure is "correct"? I have tried the CyclingApps Exact Tire Pressure and TyreWiz, but believe the first is better since you can adjust for dry/wet, tarmac quality and balance. What do you use to decide the optimal pressure?


If you have an iPhone, the Mavic app seems to do a good job. Not sure if there's an equivalent for Android or general web browsers.

TomA is spot on, we have been working on an algorithm for a while and the big problem is the input for the surface which can completely change the numbers. Any of these apps can give a decent starting point for your testing, but none of them are giving numbers based on any sort of testing, but rather using more or less linear interpolations to draw a line between min and max pressure for a given size. The Mavic one is decent, but still off by as much as 15% when compared to optimal in field testing.

The key is to keep a log and pay attention to the surfaces you are on.. this will be better than any app in the long run.

As for the Blackburn Honest, we haven't tested it yet, but can appreciate their nod to our 'Truth' gauge in their naming. What I can tell you is that even lower end Chinese made 1% accuracy printed circuit boards with a pressure transducers cost nearly as much from the manufacturer as they are selling an entire gauge for at retail, so unless they are losing a bunch of money on each one this is unlikely. At that price, I would imagine it is a more standard +/-3% accuracy setup with +/-1.5% repeatability. The only 1% accurate standalone gauge for presta that I know of is the one from Kappius which uses quality name brand internals and sadly, at $159 isn't priced much above the cost of the subcomponents.. We use some of the same suppliers in our SuperPista digital, Tattico BT and the (launching tomorrow) Viaggio BT pump and I can tell you that you definitely get what you pay for with these things and the good stuff isn't cheap.
https://www.kappiuscomponents.com/...gital-pressure-gauge

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
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Re: What calculator to find the correct tire pressure? [joshatsilca] [ In reply to ]
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So basically the optimal inflation pressure to minimize Crr is a function of surface roughness. I can see that keeping a log would be helpful for something like optimal pressures for different tracks, but outdoor surfaces like chip-seal would seem really difficult to classify. I assume chip size and bitumen ratio, wear,... all would affect choice.

I assume there are fancy instruments that would measure roughness, and I am amazed what you can do with cell phone technology, but it there another way to classify roughness? Contact paper,... There must have been something that engineers used before all the fancy modern instrumentation.
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Re: What calculator to find the correct tire pressure? [grumpier.mike] [ In reply to ]
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So the engineers can classify and measure surface roughness all day long.. the problem is that the customer/app user cannot as the tools are quite expensive and specialized. We have been building a database of images to serve as a sort of proxy for a measurement, but with so many methods of building road surfaces to begin with, combined with so many ways for them to wear and degrade it turns out to be a lot harder than it sounds. So far we've found that photos + a personal log + experience are the most potent combination since rider feel/perception can serve as a nice sanity check compared to what the surface looked like.

The other advantage to the log is that really any ride or race is going to be over a mix of surfaces, so it's super helpful to have the experience of knowing the mix of surfaces so that you can make the best overall decisions for an event. With our pro teams we found nobody wanted to keep a log or do the post race report on what could/should have changed, but in subsequent years they found that having that info paid massive dividends and they are able to go into a race weekend with tire choice and pressure dialed even for new riders as they have such a strong basis from the history. Each year the log gets refined even further, and as new events pop up or courses change, it's fun to see the mechanics use the log to draw similarities to create starting points. In the end, it's a huge time saver, and quite honestly, it's a pretty big tactical advantage for the team.

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
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Re: What calculator to find the correct tire pressure? [Allanhov] [ In reply to ]
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N = N-20

Eric Reid
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Re: What calculator to find the correct tire pressure? [Allanhov] [ In reply to ]
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Allanhov wrote:
I understand tire pressure is very important for rolling resistance and aerodynamics. To ensure that I have the correct pressure I bought a Blackburn Honest Pressure Gauge (https://www.blackburndesign.com/...-pressure-gauge.html) with a claimed accuracy of 1%.

But how do you know what pressure is "correct"? I have tried the CyclingApps Exact Tire Pressure and TyreWiz, but believe the first is better since you can adjust for dry/wet, tarmac quality and balance. What do you use to decide the optimal pressure?

Here is different take. You and others are chasing rolling resistance and aerodynamics without consideration to the beating your body could take if you optimize only for rolling resistance and aerodynamics.

An important function of tires is deflection. Regardless of what is on the tire or what is on a website, if your tire doesn't give when riding you are tiring yourself out. There is an energy cost to you when you are the shock absorber rather than tire helping.

Given my own advice I ride with just 70lbs on the front wheel and 100lbs on the back of my 25s. Any higher than that, I no longer feel the benefit of their give over rough roads. I weigh 145 lbs and loaded bike another 20lbs.

https://janheine.wordpress.com/...-tires-and-pressure/


"Suspension losses are caused by friction in the the rider’s body tissues as they are vibrating. Higher pressures cause more vibrations, and hence higher suspension losses. This appears to cancel any gains at higher pressures from reduced flexing of the tire (hysteretic losses), as the tire deforms less at the contact patch as the wheel rotates."

Indoor Triathlete
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Re: What calculator to find the correct tire pressure? [Tom A.] [ In reply to ]
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Tom A. wrote:

I usually figure out the rear load, and then drop the front pressure by 5-10% based on the bike setup.

If the weight distribution is 50/50, which is the case when I ride in aero position, would you still have a lower pressure in the front tire?

3 x Norseman winner - http://www.triallan.com
Ambassador of:
Quintana Roo - https://quintanarootri.com
Morf-Tech - http://www.morf-tech.com
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Re: What calculator to find the correct tire pressure? [Allanhov] [ In reply to ]
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Allanhov wrote:
Tom A. wrote:


I usually figure out the rear load, and then drop the front pressure by 5-10% based on the bike setup.


If the weight distribution is 50/50, which is the case when I ride in aero position, would you still have a lower pressure in the front tire?

No. If that's the case (it's rarely, if ever that for me, even on the TT bike...I like my TT bike to have quite a bit of front-center length), then I'd just inflate them equally.



http://bikeblather.blogspot.com/
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Re: What calculator to find the correct tire pressure? [joshatsilca] [ In reply to ]
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joshatsilca wrote:
sathomasga wrote:
Allanhov wrote:
I understand tire pressure is very important for rolling resistance and aerodynamics. To ensure that I have the correct pressure I bought a Blackburn Honest Pressure Gauge (https://www.blackburndesign.com/...-pressure-gauge.html) with a claimed accuracy of 1%.

But how do you know what pressure is "correct"? I have tried the CyclingApps Exact Tire Pressure and TyreWiz, but believe the first is better since you can adjust for dry/wet, tarmac quality and balance. What do you use to decide the optimal pressure?


If you have an iPhone, the Mavic app seems to do a good job. Not sure if there's an equivalent for Android or general web browsers.


TomA is spot on, we have been working on an algorithm for a while and the big problem is the input for the surface which can completely change the numbers. Any of these apps can give a decent starting point for your testing, but none of them are giving numbers based on any sort of testing, but rather using more or less linear interpolations to draw a line between min and max pressure for a given size. The Mavic one is decent, but still off by as much as 15% when compared to optimal in field testing.

The key is to keep a log and pay attention to the surfaces you are on.. this will be better than any app in the long run.

Hi Josh and thanks a lot for the reply. I loved the podcast with Flo Cycling and have now read all your blog posts about the subject.

Everything should be made as simple as possible, but not simpler.

I am not looking for a simple answer, if that is not possible to give. Still, I have to find a "correct" pressure. From a practical perspective I will use the calculator from FastFitnessTips (https://www.youtube.com/watch?v=Clk_LLBYFzA) as a baseline if no one have a better calculator. Then I will adjust according to field testing and feeling of handling.

3 x Norseman winner - http://www.triallan.com
Ambassador of:
Quintana Roo - https://quintanarootri.com
Morf-Tech - http://www.morf-tech.com
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Re: What calculator to find the correct tire pressure? [joshatsilca] [ In reply to ]
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joshatsilca wrote:

As for the Blackburn Honest, we haven't tested it yet, but can appreciate their nod to our 'Truth' gauge in their naming. What I can tell you is that even lower end Chinese made 1% accuracy printed circuit boards with a pressure transducers cost nearly as much from the manufacturer as they are selling an entire gauge for at retail, so unless they are losing a bunch of money on each one this is unlikely. At that price, I would imagine it is a more standard +/-3% accuracy setup with +/-1.5% repeatability. The only 1% accurate standalone gauge for presta that I know of is the one from Kappius which uses quality name brand internals and sadly, at $159 isn't priced much above the cost of the subcomponents.. We use some of the same suppliers in our SuperPista digital, Tattico BT and the (launching tomorrow) Viaggio BT pump and I can tell you that you definitely get what you pay for with these things and the good stuff isn't cheap.
https://www.kappiuscomponents.com/...gital-pressure-gauge

I dont believe the Blackburn Honest claimed accuracy of +/-1% either. As I work in the oil industry I have the possibility to test it against fiscal measuring device with guaranteed accuracy of +/-1%. I just have to build some connections and remember to bring my Blackburn with me.

I am looking for a better solution to measure pressure, and understand that quality cost. Getting the Kappius Digital Gauge shipped and taxed to Norway would be cost $217, which is not far of from the Viaggio BT. Is the accuracy similar? I have a specialized travel pump, so no need of a travel pump, but I could change it with a Viaggio. Is the Accuracy of the Tattico lower or similar?

3 x Norseman winner - http://www.triallan.com
Ambassador of:
Quintana Roo - https://quintanarootri.com
Morf-Tech - http://www.morf-tech.com
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Re: What calculator to find the correct tire pressure? [Allanhov] [ In reply to ]
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Allanhov wrote:
I understand tire pressure is very important for rolling resistance and aerodynamics. To ensure that I have the correct pressure I bought a Blackburn Honest Pressure Gauge (https://www.blackburndesign.com/...-pressure-gauge.html) with a claimed accuracy of 1%.

But how do you know what pressure is "correct"? I have tried the CyclingApps Exact Tire Pressure and TyreWiz, but believe the first is better since you can adjust for dry/wet, tarmac quality and balance. What do you use to decide the optimal pressure?

Same question for me. I've just set up a bike with HED Belgium+ wheels (21mm internal) and Compass Stampede Pass (32mm) tire. I weigh 168 lbs, the bike- a Black Mountain Cycles Road- weighs 22 lbs. I've consulted 3 apps for tire pressure and they are all over the place:

MyMavic app (nice that it accounts for internal rim width) suggests 73/73 F/R psi.
Berto Tire Pressure Calculator app suggests 45/69 F/R psi.
TyreWiz app suggests 50/53 F/R psi.

Pretty wide swing.

The Berto Chart (from Bicycle Quarterly) is somewhere in the middle if I assume a 45-55 front rear weight distribution, I get with my uncalibrated eyeball 49-50 front and 59-60 rear.




I'm going to start at 65 front and 70 rear and then drop 5 psi each ride for the next few rides until I get to 50/55 and see what works. Thoughts from the tire pressure gurus?

Suffer Well.
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Re: What calculator to find the correct tire pressure? [jmh] [ In reply to ]
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I always go equal pressure.

Braking puts a lot of force into your front tire.
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Re: What calculator to find the correct tire pressure? [NordicSkier] [ In reply to ]
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I am running GP 5000 tires with silica latex tubes. Measured installed width is 23 mm. weight 145lbs with approximately 20lbs of Trek Speed Concept.

I have been running 90lbs in front and rear in training on mixed surface but all good roads. I know this cannot be completely accurate but what ball park PSI would you suggest erring on the low side of the break point?

BTW... the mavic app says 107 front and 112 rear. Based on what I have read here, that is about 25 PSI too high
Last edited by: Calvin386: May 2, 19 12:35
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