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Tire pressure monitoring system

PostPosted: Thu Jan 20, 2022 11:06 am
by HMF
A couple of questions about the BMW TPM system for the BMWBMW tech gurus:

What is the difference between "Tire pressure within the permissible tolerance." and "Tire pressure within the limit range of the permissible tolerance." ? This comes from the Technology in Detail section of my owners manual.

The bigger question, regarding temperature compensation: Let's say the ambient temperature is 40 F and I fill my cold tires to the recommended 36/42 psi. During the ride, my TPM reads 39/45, which I always assumed was normal, and so ignored. However, if those TPM readings are compensated to 68 F, that means I had actually over-inflated my tires and should actually have inflated them to 33/39 at 40 F, so that the TPM would read 36/42 when warm.

Am I off the mark here?

Thanks for your help.

Re: Tire pressure monitoring system

PostPosted: Thu Jan 20, 2022 2:49 pm
by JimVonBaden
Hi Henry,

The definitions are functionally the same.

As for your question on temps, the pressure you put in at 40° will be realistically the same at 68°. However, your pressure will go up and down based on tire heat, which expands and shrinks in pressure some as the tires heat from use.

In other words, don't sweat the differences. Set the pressure using a gage and it will be fine.