Thread: TPMS issue?
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      12-04-2012, 07:51 PM   #24
Major General

Drives: 335i Msport w/sport AT
Join Date: Mar 2006
Location: Chicago

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Originally Posted by bavarianx View Post
30psi is close to the cutoff for low pressure warning, you may want to run about 33-34psi, since temp will make the pressure change +/-1-2 psi
Does the system actually have a preset low pressure cut off at 30psi?

It makes sense that there would be some level at which the system triggers "too low", I just wonder if it really is 30psi.

From my understanding the reason we can set/reset the TPMS is because drivers can set the air pressure as they need it for either high sustained speed travel, "average" speed travel, or perhaps adjusting it to handling or ride differences. Then, based on the pressure one puts in they reset the TPMS to that psi, which now becomes the set point.
If the pressure drops by a certain psi, then the warning is triggered.
I'm not sure how much drop there needs to be before the warning?
Is it 3psi, 5psi, or more?

So, if you set the TPMS at 32psi, for whatever reason, and it's 70F outside, then the ambient temps drops to 50F, there will be a 2psi drop in cold tire pressure. Normally I don't think that's enough to trigger a warning.
But if the built in nominal is 30F, then there will be a warning.

Interesting that you brought up a nominal preset point for a warning.
Did you read that info somewhere? Could you post a link if you have or remember it?