Tyre Pressure Indicator

[Smitty]

Warning light came on during the commute to work this morning. Stopped immediatly and seemed to be no problem. Reset the the sensor once I got going again - it stopped flashing but didn't go out. :confused:

Just went out to the car in the car park - all tyres seem fine.

I'll obviously check the pressures tonight, but anyone else had a rough "bong" from the sensor?

[GCA3N]

Warning light came on during the commute to work this morning. Stopped immediatly and seemed to be no problem. Reset the the sensor once I got going again - it stopped flashing but didn't go out. :confused:

Just went out to the car in the car park - all tyres seem fine.

I'll obviously check the pressures tonight, but anyone else had a rough "bong" from the sensor?


I had this when I first got the car got out and checked the tyre pressures and they were all the same (different story here but they were all at 60PSI :eek:, and it had just been released from the garage) anyway found it strange. About a week later I took the wheels off to clean (pressures now at 35 psi no problems) then and I noticed a nail through the centre of one of the tyres. I don't know if this had happened at the time or not. Anyway got the tyre repaired and never had a problem since.
Might be worth taking them off to have a closer inspection.

[Smitty]

I know there is a nail in my rear right run flat but it is properly plugged in and about the inch from the side so it's not repairable. Decided since there was no leak, probably best just to leave it in there. It's been in for well over 6 month nows with no issues but perhaps it's been dislodged.

Will check the pressures on the way home!

[Craig]

yeah I've had the occasional bong and found nothing wrong. :rolleyes: Weird, but better to be safe than sorry. ;)

[C.Noble]

The tyre pressure warning system on the MINI is quite clever, but a bit too complicated for its own good sometimes...

Its fitted to the MINI because ALL cars sold with run flats MUST have a system to warn the driver of a puncture or an under inflated tyre as it cant be as easily detected by a driver like it is to feel a conventional tyre running 'flat'.

Unlike some other manufacturers who use little inductive type sensors mounted within the whee/tyre itself (like Renaults where the sensor is at the base of the valve), BMW use the wheel speed sensors to detect variations in wheel speed relative to each other, it is part of the ABS/DSC system (hence why the puncture warning lamp comes on when the ABS/DSC light comes on).

The theory behind the system is that an under inflated tyre 'shrinks' and therefore has a slightly lesser circumferance than a correctly inflated tyre, therefore at lower speeds it turns more times a minute than the other wheels, similarly at higher speeds, the tyre begins to bulge out in the middle more because the inflation pressure is not strong enough to stop the tyre deforming because of centrifugal force, therefore that wheel speeds drop relative to the others as the vehicle speed increases.

Because the system is purely comparing the speeds to each other, it will not detect 4 equally over inflated tyres (as in your case Craig) or even 4 totally flat tyres.

As I said, it is all quite complex, using lots of mathematical calculations on minute variations in 4 different wheel speeds, compensating for loads of diferent variables like tyre wear, cornering, manufacturing tolerances of the tyre and wheel, etc. This is why the system needs 'reset' regularly (once a week when you check your tyre pressures:hand:) to stop it being confused by all these other factors adding up to convincing the computers that there is a puncture when there isnt.

I know the system I researched for putting in to a training course, it was capable of detecting a 5 psi drop in pressure within 15 kms of driving. So it is quite possible that your nail in the tread is indeed leaking out air.

[GCA3N]

I know there is a nail in my rear right run flat but it is properly plugged in and about the inch from the side so it's not repairable. Decided since there was no leak, probably best just to leave it in there. It's been in for well over 6 month nows with no issues but perhaps it's been dislodged.

Will check the pressures on the way home!


Maybe wrong here but probably a good idea to sort it, can't see it being very safe. Like i say might be totally over reactiing.

[Smitty]

Maybe wrong here but probably a good idea to sort it, can't see it being very safe. Like i say might be totally over reactiing.

Nah, it's ok Greig. I got it checked by some tyre fitters and they said it would be fine - and just to run with it until it started to loose pressure.

Would I get it fixed if had had the cash - yes, I'd love Toyo's all round....but at £120 a corner I'll hold off until it starts to fail :yes nod: Afterall, it's been like that for 6 months!! :Whistle: :p

And C.Noble - your a geek :eek: ;) But thanks for the detail - that was really interesting finding out how it works!

[GCA3N]

Cool, but you not could get a puncture repair done.

Mr noble fab explanation

[antihero3000]

yeah I've had the occasional bong and found nothing wrong. :rolleyes: Weird, but better to be safe than sorry. ;)

Me too, get it every few months. Get out and check 'em and they're fine so just reset it :confused:

[Forbes]

I'd love Toyo's all round....but at £120 a corner I'll hold off until it starts to fail :yes nod:

What tyres you getting? Proxies T1-R? I can get them for £70 each and Ryan found 4 for £225 on eBay. In 205/45/17