When replacing tyres last year i noticed there were no sensors on them, I wasnt too bothered, a few weeks later the car bonged with trye defect. I ignored it and following morning one of the tyres was a bil low. Upon investigation i found a screw was in the tyre, Got that repaired and put it down to a coincedence, This has happened again resulting in a new tyre this time. Again no sensor
Now on wed this week it bonged for the fourth journey in succession so i checked the tyre pressures and rear drivers side was at 21psi and the rest between 32-34. I obviously topped up and nothing since
Question is, how the hell is this happening when there are no sensors on the valves. Or is there a much more intelligent system on these cars??
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Steve Mac
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It doesnt use anything in the valve, it works on the ABS sensor to monitor rotation. A deflated tyre (mine pings when it has dropped half a bar) is picked up owing to the decreased rolling diameter.
Neil.D
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No internal tire sensors are used. The DSC/ABS brain keeps track of tire rotational speed, so when one tire loses a significant amount of pressure, the rotational speed of that tire will change relative to the other 3 and the warning light let's you know.(or something like that)
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Last edited by ECB; 12th October 2008 at 13:27.
Reason: Neil beat me to it
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IIRC the system used in BMWs is a Flat Tire Warning (FTW) not a Tire Pressure Monitor (TPM). FTW works by comparing the number of revolutions of each wheel to determine if one tire is low. The theory behind it is based on the fact that with lower pressure, tire diameter is reduced and the affected wheel rotates faster than other wheels at any given speed. There are no pressure sensors.
TPM uses a sensor in each wheel to monitor the pressure in that tire. After-market TPM sytems are available.
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You should fill the tires to the correct pressure for you (I run more pressure than recommended on the door jam), and then reset the sensor. The reset button is on the dashboard, and then drive it for at least 15 minutes after resetting.
I got a (near) flat on a brand new set of tires two weeks ago. The "Tire Defect" signal was displayed, and I stopped. The nail impregnated tire (2 screws, rear) was 23% below the other rear (I had read that it can go as low as 30% less, before it registers). First "Tire Defect" signal I have ever gotten (in 5.5 years), but the other flat I had was at speed (over 120 MPH), and never registered. I had since read (BMW documentation) that the tire sensor doesn't register if you are going over 95 or 105 MPH (can't remember which).
But, if properly set (and, you are going less than 95 MPH or so, which isn't easy), they do work. And, thank heavens they work. If it hadn't worked, I would have ruined a brand new tire. The pressure in the tire that was going flat was 34.5 lbs. The other rear was 44.5 lbs. (Warm tires)
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. Again no sensor
Titanium silver
Linear Mode
