Low Tire Pressures

For the last few days I've gotten low pressure warnings from the TPMS. The system indicated that all four tires were low, so I assumed it was triggered by the low temperature we've experienced lately. I drive carefully until the first stoplight, reset the TPMS, and took off without any issues when I got in the car later in the day when it was warmer (80s v. 50s to 60s in the AM).

I manually checked the pressures this morning, and they were all in the 24.5 to 27.0 psi range (the sticker in door sill recommends 38 psi for speeds < 100 mph). I was a little surprised at this level given the car TPMS read green once it warmed up and the system was reset. I wonder what the cut-off is for registering as acceptable; 24.5 just seemed awfully low.

I filled up all the tires to 38 psi this AM before leaving home, reset the TPMS, and went on my way without any problems.

Supposedly TPMS sensors in general have difficulty holding air when the temperature drops, or so a guy at a tire shop told me. I wouldn't ignore the TPMS warning, but instead check your pressure and top off accordingly. Of course, I reset mine to turn it off and have yet to get the compressor fired up to check the tires...

Mike

Originally Posted by southern6er22

I manually checked the pressures this morning, and they were all in the 24.5 to 27.0 psi range (the sticker in door sill recommends 38 psi for speeds < 100 mph).

These pressures are WAY too low. You are probably fast destroying them, especially the rears.

The lowest my sticker in the door says, at any speed, is 37psi (260kPa) front, 40psi (280kPa) rear. I normally inflate to 40 psi front, 43 psi rear cold when I reset.

This is another issue with RFTs. Because they are designed to run on no pressure for a limited time / distance, you do not notice when they are under-inflated. BUT, you are putting most of the load (and wear) on the two side-wall areas, and they wear disproportionately. I destroyed two rears on a 335i in less than 12,000 miles. The steel bands were protruding on the outer sides of the wear area, with lots of groove left in the middle.

Go get some air. (In your tyres.)

R.

From the USA manual - speeds up to 100mph - it says 38 psi front and rear for our rims / tyres.

R.

When you reset the TPMS, it will accept the current pressure as the new normal. Therefore, you should not reset the TPMS until you have refilled the tires to the required pressures.

The pressure monitoring system is widely misunderstood. Wmcilwain is right. And further, it is purely relative measure.

Again, from the trusty old manual...

R.

Hopefully I didn't do any permanent damage. Thanks for the info, guys.

So, since I filled them all to 38 psi and immediately reset the TPMS, does that mean that I have set the normal back to 38 psi or do I have to do anything else? Thanks for the help!

Glad I switched my lead boots for my aluminum trainers since I started getting this warning

This thread is another good reason why the TPMS should read inn PSI. When you get a low pressure warning there's no way to know how low you are. I have read some BMW owners have done coding to show PSI in the readout, but kind of a hassle. They really should make it visible from the factory to male this easier.

They should have the manual's comment about setting the current psi as the new normal in the warning screen that appears in iDrive. That would be beneficial and prevent a potentially dangerous situation. Saying, "don't run over children and try to sue us because you relied solely on the backup camera when backing out" is a bit more obvious than the fine print from the manual about the TPMS.

^^ haha....

In case you needed further confirmation, my car came back after a service. I have a very accurate professional tyre inflator, so I wanted to see what pressures the dealership used.

To their credit my dealership (Westside Brisbane) did a good job, as they have always done for me. The two fronts were exactly the same, as were the rears.

This is what it was:

Front: 275 kPa (40 Psi)
Rear: 295 kPa (43 Psi)

The biggest mistake you can made with RFTs is too run them at too low a pressure. You don't notice it that much, until you one day look at the wear pattern...

R.

I wore out the Bridgestone RFT's on my 335 by not routinely checking pressure often and only relying on TPMS, and you often don't even notice the wear as its often concentrated on the inner tyre. 6's in the UK are now shod with Dunlops, I've heard they wear better, but I strongly agree that regular checks (every 6-8wks) and pressures of 38psi are advisable. New boots can be costly!!

Originally Posted by roadsta

In case you needed further confirmation, my car came back after a service. I have a very accurate professional tyre inflator, so I wanted to see what pressures the dealership used.

To their credit my dealership (Westside Brisbane) did a good job, as they have always done for me. The two fronts were exactly the same, as were the rears.

This is what it was:

Front: 275 kPa (40 Psi)
Rear: 295 kPa (43 Psi)

The biggest mistake you can made with RFTs is too run them at too low a pressure. You don't notice it that much, until you one day look at the wear pattern...

R.

How many times per month would you recommend to check the tires' air pressure?

BMW would say about once every 4-6wks, you'll notice that the pressure hasn't dropped that much, but you will prolong your tyres!

For 20 inch rims, I was thinking perhaps twice a month at a minimum, especially how the tire pressure is so high and temperature sensitive?

If one is near a Costco, they are great at checking and setting the tires at the proper pressure, using nitrogen, and for free!!

Too bad Costco doesn't carry the 20's i need for my 356 wheels ... Getting on 20k miles and it's time for new rubber bands

Originally Posted by Ace535i

If one is near a Costco, they are great at checking and setting the tires at the proper pressure, using nitrogen, and for free!!

We don't have a Costco. My city sucksssss.

Originally Posted by long time

Too bad Costco doesn't carry the 20's i need for my 356 wheels ... Getting on 20k miles and it's time for new rubber bands

There's rubber on them? I thought it was $450 for a coat of thick pain on the rims

Edit - *thick coat of paint - Freudian slip