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Old 01-05-2023, 06:51 PM   #1216 (permalink)
JSH
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Quote:
Originally Posted by redpoint5 View Post
I too thought TPMS as a legal requirement was absurd, but then you had a bunch of dummies flipping SUVs on Firestone tires because they ran them severely underinflated.

I'd know if a tire was down 10lbs, and I check them at least twice a year or on longer trips.

Using the wheel speed sensor makes a lot of sense, though I wonder how it compensates for tire wear or different tires?

I'd think emergency automatic braking would be more of a safety requirement than an idiot light for tire pressure.
With an indirect TPMS system the computer is just comparing RPM between the wheels. If one wheel starts turning faster than the others the effective diameter is smaller and therefore the tire must be low. (Our you put on a different size wheel) Federal law requires a TPMS to trigger when a tire is 25% below the recommended pressure.

Indirect systems are cheap but they have limitations. My 2014 Jetta Sportwagen at indirect TPMS that failed to warn me that I had a puncture on a gravel road because it doesn't work below a certain vehicle speed. We came back from a 3 day backpacking trip to find a completely flat tire. They also don't work if all your tires are equally low - which is what happens when someone never checks their tire pressure and adds air to make up for the normal loss of air pressure over time.
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