XSeries-forum

Hello can anyone help - last week my run flat light come on red I found the nearest garage and topped up the air in my tyres lowest was on 30psi. Max on my tyres is 50psi. reset the run flat indicator and off I went. Fast forward a week it comes on again, red. Found the nearest garage all tyres have correct pressure in them.
Has anyone had or know what this problem might be?
Thanks in advance

Are all the tyres at the correct 2.2bar (32psi)?

The warning light is triggered by differences in the rotation speed of the wheel as monitored by the ABS.  A different tread pattern or wide wear variation can trigger it.

If you have a 4.4/4.6/4.8 engine then they have a radio transmitter tyre pressure system and you may have a bad transmitter.

Richard

No 32psi was what they was on more or less when the run flat indicator come on he first time. On inspection the tyre walls did seem to be bulging out the sides slightly especially on the wheel where most of the weight was sitting, if you catch my drift.

So I inflated them to 10% less then the max (50psi) stated on the tyre, so 45psi each wheel. The bulging was no more and the steering was lighter at lower speeds where as before it was kinda heavy...

A week later the r.f indicator came on again.

Btw I have a 3.0i the tyres are 35mm low profiles 20s - 285 on the front 315 on the back (off the top of my head)...

45psi will mean the centres wear much quicker.  2.2bar/32psi is the recommended pressure.  These cars are going to feel heavy - they weigh two tonnes after all!

Richard

Hi Richard. I read if tyres are quite wide the centres won't wear as much under higher pressures, I can see the logic in that. Also the 2ton weight would help ensure more even tyre wear across the wheel.
I know what your saying but to me when I was checking the first time when the tyres had the 'recommended' pressure in them the tyre wall bulge ment the alloy rim was precariously low to the tarmac. My thoughts being if I hit a pot hole or similar I might have some serious trouble arise.
Is that the recommended pressure for a standard tyre which came with the car or does it apply to any alloy and tyre? Being low profiles I would think more psi is required?

BMW Recommended pressure for 19" & 20" wheels & tyres with a normal 'load'.  There is (or should be) a plate on the driver's door 'B' pillar that lists pressures for sizes, tyres, wheels and payload.

Richard

Just to add, even at 32psi the centres will wear quicker than the outside edges, in my experience. That's with Diamaris on 20" rims. I've dropped my rears to 30 but not got enough miles on it since the change to see if it's making a difference.

Fronts don't seem to be quite so critical as they are wearing evenly at 32.