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Optimus Prime
08-12-2009, 01:03 AM
It's my understanding that with the e90 generation there are no longer bands around the wheels that send the pressure info to the car. Instead the ABS rings report specific rotation speed and that when one tire gets low, the rotation speed increases due to circumference change.

Is this correct?

SARAFIL
08-12-2009, 01:10 AM
It's my understanding that with the e90 generation there are no longer bands around the wheels that send the pressure info to the car. Instead the ABS rings report specific rotation speed and that when one tire gets low, the rotation speed increases due to circumference change.

Is this correct?

No, I think you have it backwards. They used to use the rotation speed of the wheels, but now due to more strict regulations they have actual tire pressure sensors mounted inside each wheel, they are on the inside of the wheel directly vehicle the valve stems. They communicate the pressure to the computer.

JST
08-12-2009, 06:36 AM
Depends on the year. My 2007 335 had a rotation speed sensing system; my 2008 M3 has a direct sensing system like the one Sarafil describes. I know this because I had to get sensors for the M3's snow tires, and didn't have to for the 335.

TD
08-12-2009, 07:04 AM
No sensors in my former '06.

equ
08-12-2009, 07:05 AM
My two 2006 e90's did not have TPMS, just the rotation counter to alert...

SARAFIL
08-12-2009, 10:36 AM
I was not sure when they changed over, but it looks like it was sometime during the 2007 model year or possibly at the beginning of 2008 based on the responses above. All new BMWs/MINIs (any model) and probably many other cars on the market these days will have a "direct" TPMS which requires a sensor in each wheel.

Optimus Prime
08-12-2009, 11:36 AM
I was not sure when they changed over, but it looks like it was sometime during the 2007 model year or possibly at the beginning of 2008 based on the responses above. All new BMWs/MINIs (any model) and probably many other cars on the market these days will have a "direct" TPMS which requires a sensor in each wheel.
Are these a different sensor than the band that used to be around the inside of the wheels? I thought that's what they had originally, then switched to using the ABS rings. Maybe they've again switched that and they have a sensor on the inside of the valve. :dunno:

Terri Kennedy
08-12-2009, 11:53 AM
Maybe they've again switched that and they have a sensor on the inside of the valve. :dunno:
That's what it looks like. I just checked the BMWUSA configurator (stock 328i) and it comes with Style 282 wheels. The ETK page for that wheel shows a transmitter in the valve stem. See attached PDF.

SARAFIL
08-12-2009, 11:56 AM
These are the actual sensors that they use.

Terri Kennedy
08-12-2009, 12:08 PM
These are the actual sensors that they use.

Yikes! $79.14 each? And that's just for the electronics module; doesn't even come with the funky valve stem, which is another $13.90! :irate:

Any idea why that part has a note that says "Important! Limited storage life: Please observe expiry date on parts label."?

SARAFIL
08-12-2009, 12:24 PM
Yikes! $79.14 each? And that's just for the electronics module; doesn't even come with the funky valve stem, which is another $13.90! :irate:

Any idea why that part has a note that says "Important! Limited storage life: Please observe expiry date on parts label."?

Yeah, they are not cheap!

Not sure what the limited life is, I assume they are battery powered?

JST
08-12-2009, 12:28 PM
Yikes! $79.14 each? And that's just for the electronics module; doesn't even come with the funky valve stem, which is another $13.90! :irate:

Any idea why that part has a note that says "Important! Limited storage life: Please observe expiry date on parts label."?

Do they have batteries inside?

I got TPMS sensors from TireRack that work fine with the BMW and I am certain that they were less than $80 (or $93) a wheel, though I cannot remember exactly how much they were.

Terri Kennedy
08-12-2009, 12:45 PM
Not sure what the limited life is, I assume they are battery powered?
Hmmm. A non-rechargable Lithium-Ion battery should have a shelf life of 10+ years. If the unit was pulling enough power to run down the battery while in inventory, they could have designed it to only activate the first time it saw pressure.

Presumably they're designed to last longer than the 3 year new car warranty.

I can just see the reaction a service advisor would get when telling a customer "Yup, that'll be $316.56 for the 4 sensors, $300 for labor, and $80 for dismounting and mounting the tires." :lol:

Even if you could replace the batteries, that'd still be a pretty steep tab for the labor + mounting.

I wonder if these could be powered from the rotational energy of the wheels turning?

Semi-related - the 63-1114 (http://www.radioshack.com/graphics/uc/rsk/Support/ProductManuals/6301114_PM_EN.pdf) tire pressure gauges that Radio Shack was peddling some years ago had 2 sets of batteries - one for the backlight, which could be replaced by the customer, and one for the electronics and display, which was not user-replaceable. Of course, since I never used the backlight, the main battery would fail first (their claim of a service life of 30,000 readings was wildly optimistic). The first time I tried changing it, I discovered that the sensor used in the unit was so inconsistent from unit-to-unit that each gauge had to be calibrated at the factory, and if you disconnected the battery the unit wouldn't work again because it lost its calibration. Not that I particularly care, but if I ever had to change the battery in another one (instead of throwing them out and buying better units that didn't have this problem), I'd jumper a temporary battery in place before replacing the main one.

The only time I've seen something this idiotic done intentionally was on the CPS 2 (http://en.wikipedia.org/wiki/CP_System_II) video game cards, to try to prevent them from being copied (disconnecting the battery erases the decryption key).

Rob
08-12-2009, 07:49 PM
I think it's pretty easy to tell which you have. The sensor style has cheesy plastic caps because the metal ones caused corrosion of the sensor.