BMW R1200RT/R1250RT Forum

PR4 on a 2016 RT::>>

In my last tours, I took off from places in the low 50s temp and ended up at mid day in in 93 deg.


Now it seems to me, if I checked my PSI in the early morning when I took off and set my pressure to 36/42 per mother Beemer instructions, by the time I am into the 90s temp the original 36/42 is not relatively correct.


I have struggle with this dilemma as to whether or not I should lower the pressure when I hit 40 degree difference from the start setting, and how much to lower.


then there is the TPM: randomly showing psi measurements that are off from reality


I am not through whining: how about when I am up in the mountain when the air is thinner, say 4k feet above sea, the TPM was showing a weird reading also. How do I compensate for that?

Check the pressures before your ride with a trusted tyre pressure gauge, job done. Use the TPS (RDC)  as a warning of any loss of pressure. You will receive 2 warnings, the final one being the General Warning Triangle which will flash "Red". That's how it works on the Twincam. Incidently, if I check my pressures with my gauge before a ride at 36/42 psi and re-check with the TPS (RDC) a couple of minutes after riding away I get the same reading. As regards the displayed pressure (TPS) at higher altitudes I can't really see how that would make any difference. It's the pressure "inside" the tyre which is important. Last autumn I checked my pressures at our overnight lodgings (Altitude 800FT) then we rode to the summit of Mount Ventoux (Provence) which is 6000 ft above sea level. Never had any warning indications concerning "out of tolerance" tyre pressures, and I didn't feel any need to scroll through the multifunction display to check what the TPS was registering either.

Pressures should be set with tyres cold.  If you check them later with the same gauge hen they are hot th reading should be higher.  If you read your handbook (radical idea I know) it explained that the TPM compensates for this.  On my bike it does but not quite normally showing a rise in pressure of about .1 Bar.

In the real world, for real world riders, there is very little reason to ever mess about with recommended tyre pressures.  [size=small]Applying Charles' law,[/size][size=78%] [/size][size=small]the pressure increase from 36psi for a temperature increase from 20C to 35C  is only 1.8psi. Even on a track day, I doubt that I ever had a tyre temperature increase of more than 20C. [/size]
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It's true that track tyres are often run at lower pressures, to allow maximum contact patch at higher temperatures but they are built differently - presumably with more wall strength to cope with lower pressure.


For mortals, stick with what the book says.


I also agree with only using TPM as a warning system.  I'd never trust it as an actual pressure gauge.