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      05-17-2010, 05:35 AM   #1
zltm089
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***Those with RUN FLAT tyres***

Though I'd share what happened to me a few days ago, although it might be common sense to most of you guys, this is for the the rest ...


I went to fill up at the petrol station which is about 10mins from my place, after filling up I decided to go for a short drive as the weather was sunny and there were plenty of eye candies about...


As I was approaching a mini roundabout (having seen a few gals walking down the road...I know...I'm still 16 in my head!!!!) ... I decided to press the gas pedal to giv the engine some noise....

But instead of coming very quickly out of the roundabout with a nice sound,
the back of my car swinged to my side!!!!


(I didn't press the throttle violently or floored it, as all i wanted to do was to get some nice exhaust tone for the ladies walking pass and to have time to check their asses out!!!! )

Luckily it was just a brief moment and there were no cars coming my way...but i was shocked...even though the DSC and DTC were fully deactivated and I'm used to driving without them now, it was dry and this shouldn't happened.

So when I got back home, I checked my rear tyre pressure....

Right one was 8psi!!!!!! ....and I saw that bloody nail!!!!....

My tyre monitor didn't send any warning.


So for those of you with runflats, I would suggest you check your tyres regularly and don't rely on the tyre pressure monitor, as an underinflated or flat tyre cannot be detected by simply looking at the tyre and handling/ safety is greatly affected!


Thats my good deed done for e90post today!

Peace!
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      05-17-2010, 06:25 AM   #2
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Thanks for that warning. I check mine every 10 days max but why didn't the tyre pressure warning system detect the pressure change.? I thought that was the whole point of it!
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      05-17-2010, 06:43 AM   #3
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Maybe you'd only just picked it up and it hadn't had time to register? I have found that after a tyre replacement/change, it can take a couple of miles to flash the warning.
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      05-17-2010, 06:49 AM   #4
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If the leak is very gradual then the system struggles to pick it up. The proper system that uses individual pressure transducers (as fitted to US cars) would have picked it up right away but the ABS sensor differential system is pretty shit.
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      05-17-2010, 06:54 AM   #5
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Quote:
Originally Posted by xenon View Post
If the leak is very gradual then the system struggles to pick it up. The proper system that uses individual pressure transducers (as fitted to US cars) would have picked it up right away but the ABS sensor differential system is pretty shit.
Shouldn't do should it? I thought it compares rotation speed of two wheels via the ABS - surely if it doing this, there must be a % difference where it registers the imbalance and would therefore not be affected by a gradual decline (unless the decline is even across both sides).

I'm more questioning my understanding than your answer
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      05-17-2010, 06:56 AM   #6
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Hi

I understood that the tyre pressure monitors only really work in the event of a sudden loss of pressure. A slow puncture will not affect things.

Problem with the RFT's is that you can't see when a tyre is low in pressure. The wifes Corsa gets checked only every couple of months on "normal" tyres, but with RFT's I reckon it's a more frequent job.

A friend of mine with a garage has seen cars come in for various jobs - some have RFT's that have only a few pounds of pressure in them - and the owners are driving around not knowing this!

Jeff
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      05-17-2010, 06:57 AM   #7
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Quote:
Originally Posted by ed335d View Post
Shouldn't do should it? I thought it compares rotation speed of two wheels via the ABS - surely if it doing this, there must be a % difference where it registers the imbalance and would therefore not be affected by a gradual decline (unless the decline is even across both sides).

I'm more questioning my understanding than your answer
Very true but I believe it looks for a relatively quick change in rotational speed during the same journey.

It's crap however it "works" as has been demonstrated.
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      05-17-2010, 07:20 AM   #8
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check mine once a fortnight, just cba to do it much more often then that..

they will be whipped off next change though, dirty things!
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      05-17-2010, 07:33 AM   #9
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Quote:
Originally Posted by BGM View Post
check mine once a fortnight, just cba to do it much more often then that..

they will be whipped off next change though, dirty things!
Quite right - although mine lasted far too long on the 335d (24k miles)
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      05-17-2010, 07:36 AM   #10
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Quote:
Originally Posted by ed335d View Post
Quite right - although mine lasted far too long on the 335d (24k miles)
rather depressingly i had 4 new ones in jan when i bought the car.. the previous owner had run three of them under inflated!!

didn't realise it had 'brand new' tyres until about a month later..

gutted!
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      05-17-2010, 07:47 AM   #11
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Quote:
Originally Posted by BGM View Post
rather depressingly i had 4 new ones in jan when i bought the car.. the previous owner had run three of them under inflated!!

didn't realise it had 'brand new' tyres until about a month later..

gutted!
This is an inherrent problem with RFT's - people forget to check and inflate them like normal tyres. I was a bit guilty of this with the 335, which led to inside rear wear. Running 0.2 bar over recommended pressure helped this.
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      05-17-2010, 07:54 AM   #12
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0.2 bar over, always
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      05-17-2010, 08:15 AM   #13
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Quote:
Originally Posted by xenon View Post
Very true but I believe it looks for a relatively quick change in rotational speed during the same journey.

It's crap however it "works" as has been demonstrated.
Not sure as this did work well in my wife's 5er. It picked up a slow puncture after it dropped about 0.3 bar (the pressure was checked about 2 weeks prior)

There would be no point to the 'reset' process if it only checks difference on each journey
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      05-17-2010, 09:55 AM   #14
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0.2 bar over from the minimun or maximum recommended pressure from the door card?
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      05-17-2010, 09:59 AM   #15
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Quote:
Originally Posted by BIGTIME View Post
0.2 bar over from the minimun or maximum recommended pressure from the door card?
max for your typical 'load'

for me.. well, just me!
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      05-17-2010, 10:12 AM   #16
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Quote:
Originally Posted by BIGTIME View Post
0.2 bar over from the minimun or maximum recommended pressure from the door card?
Thats what I ran - 0.2 over standard pressures for two-up. Noticed inside wear at 18k miles on the rears, managed to get another 6k out of them (with even wear)by running the higher presure and regularly checking pressures.
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      05-17-2010, 12:06 PM   #17
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When I got back that day, I inflated the tyre back to 40psi....

and this morning it was down to 30psi ....

The tyre pessure warning went on this morning on my way to kwik fit!!!!!!!!!!!......

I don't understand why it didn't go off the first time, when the pressure reached 8psi!!! .....
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      05-17-2010, 12:08 PM   #18
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and yes, running a few psi over the recommended pressure does help with the uneven wear problem...i noticed that my inside wear are not that bad when running a lil bit over....
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      05-17-2010, 12:13 PM   #19
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Quote:
Originally Posted by Jeff123 View Post
Hi


A friend of mine with a garage has seen cars come in for various jobs - some have RFT's that have only a few pounds of pressure in them - and the owners are driving around not knowing this!

Jeff

I wouldn't have known aswell!!!! if that "incident" didn't happen, as the car was driving "fine" until, I played with the throttle lightly....
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      05-17-2010, 01:10 PM   #20
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Quote:
Originally Posted by zltm089 View Post
When I got back that day, I inflated the tyre back to 40psi....

and this morning it was down to 30psi ....

The tyre pessure warning went on this morning on my way to kwik fit!!!!!!!!!!!......

I don't understand why it didn't go off the first time, when the pressure reached 8psi!!! .....
Have you recalibrated the system?
The OM says to perform a recalibration every time you change any pressures in any tyres.

Also as the rotational speeds are monitored, the only accurate way to determine a flat is with a degree of straight ahead driving.
I suspect the steering angle is monitored for steer-ahead, and then the rotational speeds of the axle wheels compared against a differential 'tolerance'.
Tricky to do this on a car that is cornering I would imagine, but only BMW could confirm this for sure.

Deflation in a high speed motorway situation (straight ahead) is obviously the biggest threat to safety, and the crappy RFT might save your life there

HTH?
Steve.
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      05-17-2010, 01:13 PM   #21
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hmmmmmmmmm...sorry...gona sound dumb again....what do you mean by recalibration?...
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      05-17-2010, 01:16 PM   #22
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On my iDrive display I have a window to recalibrate the sensors.
It is set whilst parked in the cars iDrive menu, and then tells you to simply drive, it does the rest automatically.
As per the owners manual... it then measures the wheel speeds during steer-ahead and sets up a reference value to comapre against.
This would be the measured speed of each wheel across the axle and they 'should' be fairly similar.
But - you have to recalibrate to allow for oddities like having different tyre brands or tread levels, as this will make one spin faster than the other.

No idea how the non-iDrive cars cope.
Anyone?
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