Tyre Pressures and Ambient Temperature

[C7]

How are tyre pressure settings, especially COLD settings, affected by ambient temperature, eg mid 20s in summer versus close to feezing in the winter (global warming notwithstanding...) ?

 

If one was to setup for say 17PSI in a cold winter garage, how would one compensate for a warm garage in the summer, or even after a run around the track in summer? Presume the running temps would be lower in the winter, higher in the summer for the same given starting COLD pressure?

 

Is there a formula somewhere, or just known best practice

 

Jim

[Jason Plato]

Try thinking about it in a different way .

 

You should be looking to achieve a *hot target pressure* , like 19 psi hot for acb10's or 21 psi for 32r's .

 

The tires cold pressure required to achieve the desired hot pressure will vary depending upon the ambient temp , track temp , camber of the wheels , length of running time ( sprint vs 30min race) .

 

Dave

[C7]

Good analogy, and makes sense. This works for most of us lot who have a reasonable interest in our cars setup, and generally have the time and inclination to work backwards from working hot pressures as above.

 

However, most car manufacturers quote cold pressures in the handbooks AFAIK, and Joe Average generally goes out and sets pressures at that - same every week if they're lreally reading the book closely! However as the manufacturer has no knowledge what the ambient temperature will be in any given climate, how can they quote consistent cold pressures? Is there a way to work out what working hot pressures they really intend the tyres to operate at?

[Jason Plato]

A good indication of the tyres desired hot working temperature can be gained by monitoring the tyre temperature imediatly after use .

 

The common way to do this is with either a temperature probe just under the surface of the tyre or a non contact infra red probe . record the temperatures at 3 points across the tyre - inside , middle , outside . the theory is that when the tyre is correctly inflated the temperature across the tyre will be consistent or that the greater temperature will be no more then the average of the temperature across the 3 points .

 

I imagine everyday cars will have a pressure based upon average intended us and tyre load - all we are doing with the temperatures , is gaining a more precise understanding of the tyres requirments , hence why manufacturers offer different pressures fro loaded , towing etc .

 

 

 

 

C7 TOP Powered by Hellier Performance 😬

South Wales AO

[Tony C]

FWIW - for large aircraft tyres the recommendation is to add up to 10% to the cold pressure, to give a reasonably accurate pressure when hot. But, as has been pointed out, how hot is hot

 

BRG Brooklands SV 😬 It seems that perfection is achieved not when there is nothing more to add, but when there is nothing more to take away. (Antoine de Saint-Exupery)

[Yorick]

Why don't you fill your tires with nitrogen?

Will cost you about 1 GBP a tire, mostly with free refills.

Almost no pressure changes when temperature rises, drops, ...

And larger molecules so less leakage.

It's even supposed to be better for the compound. The petroleum should evaprate less quick.

 

 

[Peter Carmichael]

Also, what tyre pressure do you run when you regularly drive up mountains. Do you get out half way up and drop the pressure?