BMW R1200R R1150R/T F800 K1200R R1100R/T R1250R RnineT Message Board

Recently returned from 3900 Km two up tour to Tasmania (which happens to complete my top to bottom traverse of Australia - Cape York to C0ckle Creek albeit on different motorcycles r1200r and r80gs and 15 years apart!).

Ambient temperatures ranged from 41.5 deg C to 6 deg C on this trip. This got me thinking, I believe that recommended cold pressures are based on ambient temperture of 20 C. So when checking pressures when it is 6 C you probably should compensate for the temperature difference.

I estimated that the difference between pressures at 20 C and 6 C would be about 3 psi. I found when measured it seemed closer to 5 psi in practice, but it is difficult to do a direct comparison.

Perhaps there are arguments against adjusting pressure for ambient temperature.

What do others do?

We had an excellent trip by the way, the bike and BMW luggage were flawless.

Correct me if I am wrong but doesn't BMWs tyre pressure monitor automatically compensate for the ambient temp?

To find correct pressure for your bike regardless (or irregardless, still don't know why those words mean the same thing) you should check pressure when tires are cold and then ride somewhat aggressively for 15 minutes. Check pressure again and it should have risen 10%.

If it went up more, tires are underinflated (heated up too much). If it didn't go up 10% tires are over inflated (running too cool)l

Remember, 90% of tire failures are due to UNDERinflation.

hass wrote:Correct me if I am wrong but doesn't BMWs tyre pressure monitor automatically compensate for the ambient temp?

hmmm.....to do what you are saying the bike would need an onboard comressor when temps drop and some kind of automatic air releise valve for the extremely high temps.......the bike lacks both.

So far I only know of one (there may be more) car...not a bike....that has the compressor onboard that is integrated into a system and its a HUMMER....

tire pressure monitor is just that....it simply tells you the pressure in your tires.....nothing less (when it works properly)...nothing more.....

Graf wrote:

hass wrote:Correct me if I am wrong but doesn't BMWs tyre pressure monitor automatically compensate for the ambient temp?

hmmm.....to do what you are saying the bike would need an onboard comressor when temps drop and some kind of automatic air releise valve for the extremely high temps.......the bike lacks both.

So far I only know of one (there may be more) car...not a bike....that has the compressor onboard that is integrated into a system and its a HUMMER....

tire pressure monitor is just that....it simply tells you the pressure in your tires.....nothing less (when it works properly)...nothing more.....

Please read my post again. What you are suggesting is nothing like my post. I suggested the tyre pressure monitor compensated for the ambient temperature meaning that the displayed pressure is a reading of the pressure calibrated to 20C. I am not certain it does this, I just remember reading it someplace. I certainly never suggested it adjusted the pressure!

my bad......i guess i missunderstood......

hass wrote:Correct me if I am wrong but doesn't BMWs tyre pressure monitor automatically compensate for the ambient temp?

I don't have the on-board tyre pressure monitor (now wish I did) but I think you have answered my question. If BMW adjusts their gauge to compensate then that makes two of us trying to doing it.

Graf wrote:my bad......i guess i missunderstood......

np. Been there, done that.

Remember there are two factors that determine tire pressure, the ambient temperature and the internal heat generated by the tire. So as the ambient drops, and therefore the pressure, the tire "works" a bit more, generating more heat and raising the pressure. So the effect is to some extent self-compensating.

Also, the gas law that determines all this (Boyle's Law or Charles' Law, I forget which) is based on absolute zero, which is -273 degrees C. A 20 degree temperature difference is only about a 7% difference in absolute temperature, assuming a start at 25 degrees C (298 degrees K).

Bottom line: It not a problem in the real world.