How flat does a run flat have to be?

N

NathanZ4C

Member
So over the weekend I noticed a nail in my tyre. Pressures looked ok however when checking it was only around 1.5 bar. I don't think it's been run far like it but it's hard to tell what the tyre has done before I had the car which was only recently.

Anyways the tyre is scrap. When removed the inside wall was falling to bits.

I'm now at the tyre fitters to get a set if non RF goodyear eagle f1's. This was my plan in any case but it's just been brought forward.

So my question is how flat does the tyre need to be before the indicator shows? I'm a little disappointed that I could have been driving around with that amount of pressure since I last checked them and it's now beyond repair.
 
Surprised that the tyre sensor system didn't activate to warn you. :?
Bad luck with the tyre but on the + side you get non run flats ..............and good ones at that. :thumbsup:
 
I think that my puncture indicator has come (with a slow puncture) when the pressure has dropped by about 6 psi. - not much really.

Quite surprised that yours didn't come on sooner?!
 
The system doesn't work on PSI pressure in the tyre but uses the ABS to read the difference in rotational circumference between the wheels, a flat tyre will obviously have a smaller circumference. It relies on the system being set correctly with the button after you have fitted new tyres or adjusted pressures. It seems like a cock-eyed system since RFT's retain most of their rigidity and size when 'flat'. I think the system is different on US models which work on actual PSI, but that may be an urban legend :)
 
A useful geek's guide to all things RFT, effects on handling and tyre pressure warning :)

http://www.wheels-inmotion.co.uk/bmw-run-flat-problems.php
 
To be fair I've never reset the button myself. I'm guessing that it could have been off before I had it.

I know when I viewed the car the sensor was on but I'm sure that would have been for the other wheel which had a screw in it. That was was replaced with another part worn before I picked it up. The light was off when I picked it up but I don't know how this was extinguished.

I've reset it now and the light did come on the dash so I know the light works. At least I'll be able to see a flat non run flat a bit better.
 
Ewazix said:
I think the system is different on US models which work on actual PSI, but that may be an urban legend :)
Click to expand...
From 2007 models on all US models work on actual pressure...
 
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