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03-30-2008, 01:27 PM | #1 |
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TPMS after swtich to non-RFT's
If this was answered in another post I apologize but I guess I dont understand the TPMS system coming in the 135i.
Like many here I will most likely be switching to non-RFT's after the OEM's wear out. (Unless they start dropping in price) I will also purchase a Mobilty kit for the non-RFT's. My question is how does this effect the TPMS system. Are they attached to the wheel? Are they only for RFT's? Is there a wire that needs to be reattached after a wheel swtich? I will be getting another set of wheels for the winter also. Hope someone here can explain so I will know what I will have to deal with. Maybe it's not big deal but I am ignorant as to how it operates and is attached to the wheel/tire. Thanks |
03-30-2008, 01:37 PM | #2 |
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I haven't had a look at the system BMW is using, but I have had my hands on the ones used by a lot of other companies, so I'll tell you about them. The sensor itself is mounted to the back of the valve stem. It's like two stacks of quarters placed side by side, with the stem sticking out of them. One side contains a battery, and the other side contains a small PC board with an embedded pressure sensor.
The unit sends a signal to a reciever mounted in each wheel well, that is then sent to the ECU for processing. The readings are actual pressure values, and the sensors are also capable of reading temperature for compensation purposes. They are required on every car sold in th US either this year or next year. The battery life is expected to be 10 years. The cost to manufacture is around $7/ sensor, but people have been selling them for a lot more than that. The pricing will come down to a reasonable level as production meets demand this year. A set of sensors should sell for around $100 at a dealer. The sensors are "married" to the recievers when the car is built. If you use two sets I'm not sure how they will react. I'll try to get an answer on that in a couple of weeks when I'm back in the plant that makes them in the US. |
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03-30-2008, 03:27 PM | #3 |
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They're not married. If you rotate tires or change wheels, a simple reinitialization will have everything working correctly again. Any time you change tire pressure, you need to reinitialize the system.
You can buy new sensors at the dealership or on www.tirerack.com; both cost about the same. |
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03-30-2008, 05:37 PM | #4 | |
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It must be set up so the reinitialization "marries" them again. If they weren't tied together, your car could pick up the readings from the one beside you at a light. I saw where Tirerack is selling aftermarket sensors, but the sensors don't all use the same methods. Did you see where they were selling OEM replacements for BMWs on there? |
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03-30-2008, 06:17 PM | #5 |
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If its the same system as in the new X5 then the system works with the ABS system, if it senses that one wheel is rotating faster that the others when the steering is in the straight ahead position that it warns the driver. You have to reset the system when the tyres are inflated so it gets a base line reading. If the system worked off imbedded sensors than it should notify you straight away if you stop and let 10PSI out of 1 tyre but it doesn't until you drive the car and the steering is in the straight ahead position.
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03-30-2008, 06:33 PM | #6 |
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they are sensors attached to the back of the valve stem. the sensors are not married so just make sure you have one in each wheel. and when you change to winter tires(different set of sensors) you just need to reset the TPMS through the computer control to the left of the steering wheel
these are the sensors(cheaper at the tire rack) http://www.turnermotorsport.com/html...ID=36236779490 |
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03-30-2008, 06:45 PM | #7 | |
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03-30-2008, 06:58 PM | #8 |
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good question you'd think they would be able to have a receiver that could figure out witch direction the signal was coming from. but then again the system is there just to meet safety standard so I'm sure they make it as cheep and simple as possible. not like the Porsche TPMS they tell you tire pressure in real time on the dash of each wheel.
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03-30-2008, 07:08 PM | #9 | |
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That's a different system than what's being used in the US then. It's called an indirect measurement system, and sense pressure differences using wheel speeds. The Federal government has mandated the systems here to be able to sense actual pressure. I'm not sure about the current BMWs, but on a lot of cars (even cheap cars) you can display the tire pressure from wheel to wheel right down to a PSI. The alarm may not say specifically which tire is flat, but you can look on the display and see it very easily. What they're using down under may not be the same right now. There's a pretty tight supply of the systems right now, so it's possible that the manufacturers are only using them where they're required until the production number come up. |
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03-30-2008, 07:09 PM | #10 | |
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Even cheap GM rentals cars display individual tire pressure. I'm sure there's a way to show it on the BMWs. |
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03-30-2008, 07:47 PM | #11 |
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The first E65s with TPMS showed actual pressure. I'm sure enough customers complained about 1psi differences between tires that BMW eliminated it.
The current system 'knows' actual tire pressure (you can view it on a GT1); it just doesn't display it on the car. |
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