FFT's formula #2 Adjusting tyre/tire volume pressure for temperature (Road TT Tri Cx MTB)

This is the FastFitnessTips 2nd formula for finding correct tyre volume and making pressure adjustments by temperature. For best accuracy specify type of tyre and rim size and rim width and then tyre width. If you measure these dimensions air volume should be pretty accurate (but comment below if you find any deviation). Free for non-commericial use. MS Excel required/ convert to google sheets only for your own personal use. please share by pointing to this link as XLS on the server is updated from time to time.

GOOGLE SHEETS VOLUME CALCULATOR

Google Sheets TIRE PRESSURE CALCULATOR

[jeffbrunton]

Temperature adjustment - good point.

At a triathlon where the bikes had to be left over night, they told us because of the high temperatures to leave tyres soft and top it up the next day.

Sure enough, a few people did not bother, and there were several exploding inner tubes around mid day. And it was not that hot.

We had to fly there with our bikes, and the advice when flying was also to leave the tyres soft, due to the pressure differential in the hold.

[carlosvillarreal]

I was looking at the volume inside a mining tire so I can calculate, at 125 PSI how much atmospheric pressure aire is inside.
This is a time saver!!! Thanks for allowing not to "reinvent the wheel".

[danceswithbadgers]

Handy. Since one is usually going to check one's tyre pressure indoors it makes sense to compensate for the expected outside temperature. Nice to have it quantified like this as, even if there's no time to open the Excel page a quick look at your weather app should give you, after a bit of practise, a ballpark addition/subtraction to achieve your desired pressure during your ride. Neat, thanks!

[jeffbrunton]

Great advice as always, thanks.

Deflation - I at least check the tyre pressure by feel every ride, and at least once a week with a gauge. When setting up for races, I would prepare the night before, with a track pump with its own gauge, and a more accurate hand held gauge. It does not matter if your gauge is super accurate, as long as it is consistent, which is why I prefer the hand gauge. Get one that covers the range you are using, and not wider if possible. It would be several wheel sets, mainly Dugast tubulars with hand made latex inner tubes for cyclocross. They would be softer by the next morning, race day, and need to be pumped up a bit, having dropped from say 25psi to 23psi, which at that pressure is noticeable

Road bikes - Vittorrio tubulars have latex inner tubes so also deflate after a while (but not overnight), whereas Continental tubulars have butyl, so do not deflate significantly

[gearathon]

Thanks Alex! Great stuff again! Going to pump now. 22 C indoors, 4C outdoors.Finally I can ditch the guesswork.Cheers!

[drapetomaniack]

Curious, your comment… there is a VeloNews/WheelEnergy test of Paris-Roubaix tires article where they used an air shock + rough surface to simulate the vibration losses that would be lost in rider’s body by way of heat. Interesting that they confirmed the U-shaped rr + ‘impedance’ curve the Tom Anholt and Josh Poertner observed/predicted.

One surprising thing not pointed out in article, but seems significant was that optimal pressure did NOT seem to be correlated to tire width.. and not correlated to tire rr 😳

Meaning that the assumption that a tire is just an air spring and an any differences in tire construction were negligible at best seems to be wrong!

It seems like every tire model & width on a given surface has its own curve and so predicting with a tire pressure calculator (that assumes correlation of optimal pressure with tire width) is UNFORTUNATELY not possible? The construction of the tire seems to matter to impedance.. possibly inherent resonance frequencies of the tire might matter 🤷🏽‍♂️

Comments?

[davidwoods]

Fantastic Video.  Can you direct a computer Luddite to your tyre pressure calculator?

[변성웅-qm]

Possible to get the full set of formulas with explanation from you kind sir

[tobegan]

Love your videos mate, but after watching your videos my brain hurts!

[junior-vanguardcampogrande]

Your calculations helped me a lot but i reached here searching for a more accurate way to calibrate a car tyre (which is easier because it does´n envolve a cannister)

P1/T1=P2/T2 -> P2=P1*T2/T1

And converting the temperature from K to C:

P2=P1*(T2+273)/(T1+273)

Now, such my car´s documentation asks for 32 psi on the front tyres (which is at 25ºC):

P2=32*(T2+273)/(25+273) -> P2=32*(T2+273)/298

So, if I want to know the pressure needed for a 5ºC climate:

P2=32*(5+273)/298 = 29, 85 psi

Is this valid?

[MickJabber]

Is the air already inside of the tire/tube always at room temperature? Assuming the bike has been sitting

[zazzleman]

can you do a video explaining the difference between torque and power please?

[chrisonfire]

The spreadsheet doesn't seem to be working. Can't change any of the numbers..

[Schwartz]

The link isn't hyperlinked any more for the Excel file.

[allthingsTechrelated]

My weight is 83kg or 183lbs and I’ve used an online pressure calculator which recommends that my wheels should be 222psi. Does that seem too high? The max pressure on my gp4000 S II is 115.

[Eucal]

The calculator unfortunately seems gone?

[macmurfyjka]

I just store my bike in the ambient outdoor temps. But the volume calculator is nice, for say fat bikers.