Sponsored by The Tire Rack

[Bimmer-Bob]

Okay, so one week ago I mounted a new set of 18" wheels with Dunlop Star Specs on the 1er. Rides great. Then yesterday TPMS light came on in red - I was about 8-10 PSI down on right front and rear tires. I was less than a quarter mile from home, so I finish the drive. Get home, inspect wheel and tires for damage - nothing. I know I haven't hit anything. I let the car sit. About four hours later I go out to the car, fill all the tire up to 37 PSI, and go to sleep.

Next morning I check the tires. All four are still at 37 PSI. I add 2 more PSI per tire, go run some errands for a couple of hours. No problem. Later in the evening, on the way to pick up some odds and ends for dinner, light comes on again. I pull into a gas station, top up, do my shopping. On the way home, light on AGAIN. I pull over, top up with a compressor, drive home. Reinspect tires and wheels. Still no visible damage.

So what's going on? So far, tire pressure hasn't fallen below 29 PSI. The leak has been slow, but it's clearly accelerating. I plan on taking it in to the shop first thing Monday morning, obviously, but is there anyway this could be something relatively minor? I spent about $2500 on this set up and I really don't want to replace 2 wheels and tires a week later.

One theory I have is that the valve stems aren't seated properly (I did the assembly myself) but that doesn't explain why both tires are on the same side and why the rate of air loss seems to be increasing. But with no visible damage and no history of an obvious road hazard event, I'm at a loss. Oh, and no one else has driven the car, ever.

Any ideas?

[Dackelone]

Some people have said the valve stems use a 11mm nut... this nut can become loose and let out some air. I think it is not torque too tightly. Like 3.5Nm!!! You just want it SNUG! Becarefull bc you can snap off teh valve stems! I know I checked my valve stems and all were ok. On my snows I found two stems that I could tighten a 1/4 turn.

I suspect yours are loose. Go out with a 11mm deep 1/4 socket and check yours. Just remember do not use too much force! Just make sure they are snug/tight.

IF your valve stem nuts check out ok, then check your valve stem valves. Use a really micro needle nose pliers to make sure they are tight.

[Bimmer-Bob]

Wow - I feel like an idiot! It was definitely the valve stem nuts - one of them was loose enough to unscrew with my fingers. Thanks for the quick advice and sorry if I came off as a bit of an alarmist!

[Dackelone]

Hey... no big deal. Sometimes we all over look the simple things. It always helps to have a 'fresh set of eyes" looking at a problem.

[stevenc]

Yup, had the same problem, loose valve stem.

[Project1]

and I thought I was the only one who fought with this for a week...LOL

[Novator]

Glad you posted this I have noticed the same. Filled up to 36 psi and driver's side rear has lit up the TPMS three times (once every two days) and has registered around 28 psi. I am going to go tighten those stems when work opens tomorrow (my squadron has a tire shop for aircraft wheels) Might as well make the switch to nitrogen.

[AussieRacer]

Do the spit test to work out if it is the valve stems or valves themselves. Otherwise the rim or tires could be to blame. Unlikely to have four rims with leaks though...

[laotzu]

Originally Posted by Dackelone

Like 15Nm maybe?

It's actually significantly less: 3.5Nm. I followed this suggestion trying to fix my leaky tires and ended up snapping my valve stems, completely flattening my tire.