What's the reason for these not being compatible with aftermarket rims? Granted, I haven't seen the tires taken off the stock rims, but my understanding is that the sensors are mounted to the valve stems. Is it not possible to take out those stems together with the sensors and re-use them with the new rims?
Someone please explain.

 

Ditto - as far as I thought, the sensors were just part of the valve-stem assembly and you could just pop them in an aftermarket wheel...

The owners manual mentions "the tire pressure sensor is removed from the old wheel and installed to the new one"

 

Yes, they are integral to the valve stem, but the assembly includes a small box which houses the electronics, and it's possible that some aftermarket wheels may be profiled such that there is insufficient room around the valve stem hole for the box to fit. However, I don't recall seeing anyone report finding wheels that they do not fit yet.

 

If that's the case, why does everybody with aftermarket wheels have the TPS light on? It seems that people are not re-using the stems with the new wheels - there has to be a reason for that. Or maybe they just don't know that they need to take out the stems and pop them into the new rims???

 

I think you'll find that the folks who are driving around with the light on, are those that have bought a second set of wheels for their winter tires, and neither want to go to the trouble and expense of having their summer tires dismounted to retrieve the sensors, nor want to spring another four hundred bucks for a second set of sensors.

 

Having seen the size of the TPMS when my punctured tire was replaced, it will likely fit a wide range of wheels. It will depend on the angle of the valve stem hole and the adjacent lip/ridge inside the wheel next to the hole. The sensor package is around 3"x2"x1". Tire Rack is selling the sensor now (by phone, not online) and can tell you if your wheel du jour will accept the sensor. They are still awaiting delivery of the nut/sleeve that secures the sensor to the hole for my winter package. ETA December 10. You must have the sleeve to mount the TPMS. I'm guessing once they have stock on hand for the sleeves, it will probably become an online order option. Sensors are $99 each. Sleeves are $5 each.

 

An additional $400 - $800 for sensors on top of a winter tire package with alloy wheels was neither an attractive or likely proposition to me. The TPMS is of limited value IMO.

 

I bought my RX8 in August and immediately started to check on winter tires. I ordered 17" wheels and tires from Tire Rack, unmounted. My dealer said the car would not operate without the tire pressure sensors. I e-mailed Mazda with the question and they did not reply. The dealer still does not have the sensors in stock. They priced them at $180 each. I have since sent the wheels and tires back and will be getting a ride to work when it snows until I get a winter car. Spending over $2000 for winter tires is ridiculous. I spoke with Tire Rack on 12/2 and they do have the sensors for $69. It will still be over $1500 thru them. No all-season tires are available for the car and only one 18" snow tire is available.

This is a tough situation that Mazda has put us in. Right now I have a summer car only.

 

Personally, I find the TPMS to be of dubious value and an annoyance.
Mine goes off randomly - and I have stopped each time to do a spot check right there on the road with a gauge and the tires have been at correct inflation pressures.
I think the sensors are just temperature sensitive.
Furthermore, since the system won't tell you which tire is the culprit, I consider the system an idiot light just like the braking and oil lights - if you can't be trusted to test these things on your own before you drive, a warning system isn't really of any use.

I will probably disable mine and fish the lighting wire out of the cluster harness so I don't have to look at it.
Unfortunately, just pulling the fuse sets the light.

 

The Mazda Tech Line told my dealer that lack of TPS would also cause ABS and DSC to not function, or malfunction. I have observed that this is not true. See what response you get from Mazda. The Service Manager at my dealer said he would go back to Tech Line, hopefully to get a correction.

The car should be fine for winter with proper tires. It need not be a summer-only car. It'll be enjoyable year-round.

If the TPS are so critical, Mazda could have offered a winter tire package themselves with sensors. I think they should have. They missed an opportunity. My dealer didn't offer a winter tire package either, but recommended Tire Rack.

 

Call me a complete idiot, but I didn't check my tire pressure for the first six weeks or so of my '8 ownership. The other day I used a high-quality gauge to check them, and each tire was at about 26 PSI cold. I filled them all to 32. The pressure light never illuminated either before or after this operation, or at any time during my ownership. Must have a pretty low threshold, I guess???

 

I beleive the threshold is 25 psi. A week after I received the RX-8, the evenning finally began getting cold (under 70 F) here in SoCal. The temperature was low enough to bring the pressure down and I got my first dose of low tire pressure warning.

Cold temeratures really affect tire pressure. This morning, the 8's ambient temerature sensor was reported 40 F and I when I checked the tire pressure, it was 29 psi.

 

The warning threshold can be set by the Mazda Service diagnostics computer. Factory setting was supposed to be 26 low and 49 high, I think. My low is apparently set to 28 since that was the psi when the light came once. Added air and have not had a recurrence in two months. I pumped them to 40psi for autocross and no alarm so the top end is at least 40 on mine.

Going strictly from memory, I think the technical CD showed the procedure for technicians to set the thresholds on the computer.

 

Here's the doc that says below 26 and above 49 are the thresholds:

http://www.finishlineperformance.com...02-002-03.html

Since you were at 26 psi, the lights should not have come on - so the system is working as designed. I guess the real test would be to drop them to 24 or 25 and see if the light came on?

Mine has never come on, but I keep them at 32 psi (36 psi for the winter tires).

rx8cited