[TUDM]

I have a 440i coupe with the M sport package. I have 225/40 19 in front and 255/35 19 in rear run flat tires. The car is a little over three months old and the TPMS came on stating the tire pressure was too low fronts were at 29 psi and rears at 33 psi and the door states fronts should be at 35 and rear 38. I am not a fan of these RFT ready to switch them to pilot sport. This morning I set the tires in the front to 35.5 in the front and 38.5 in the rear right away while driving I noticed that bumps were harsher but need more driving time to get a feel for handling but I do notice the car feels substantially different. Sometimes I wonder if the dealer is the best place to service sport cars. My question was does the tpms pressure as accurate as a good tire gauge because my gauge stated 33.5 in front and car states 32 and rear the gauge stated 38.5 and the car stated 37?

[Billfitz]

My TPMS reads within 0.5 PSI of what my gauge reads.

[torkles]

good way to tell would be get a friend's tire gauge and see what's right, it'll either match your gauge or match your tpms. or worst case it won't and then you'll have no idea.

[BMW11]

Originally Posted by TUDM

I have a 440i coupe with the M sport package. I have 225/40 19 in front and 255/35 19 in rear run flat tires. The car is a little over three months old and the TPMS came on stating the tire pressure was too low fronts were at 29 psi and rears at 33 psi and the door states fronts should be at 35 and rear 38. I am not a fan of these RFT ready to switch them to pilot sport. This morning I set the tires in the front to 35.5 in the front and 38.5 in the rear right away while driving I noticed that bumps were harsher but need more driving time to get a feel for handling but I do notice the car feels substantially different. Sometimes I wonder if the dealer is the best place to service sport cars. My question was does the tpms pressure as accurate as a good tire gauge because my gauge stated 33.5 in front and car states 32 and rear the gauge stated 38.5 and the car stated 37?

what kind of tire gauge are you using? are you checking the tires Cold?

[COKen]

Once you set your tire pressures are you resetting your TPMS? The TPMS will only check the current tire pressure with the tire pressure at the time the TPMS was reset.

[Billfitz]

All the reset does is to put the reference PSI to whatever the pressure is when you do the reset. For whatever reason mine was set at the factory for 34 pounds, so I got a warning at 31 pounds, when my recommended pressure was 32 pounds. That's not enough pressure swing margin in my cold climate. I filled them all to 33 pounds and did a reset, so they'd flash a warning if they went down to 30, then I deflated them back to 32.

The other reason for doing a reset is after you rotate the tires, otherwise the readouts won't correspond to the correct tire positions.

[TUDM]

Yes checked them cold and I reset TPMS after filling them to correct pressure. I am using Accutire MS-4021B digital tire pressure gauge I purchased on amazon in 2014.