My Dealer-less TPMS Tire Change Story

[redmed]

Side question: at what pressure does the TPMS throw a fit?

I believe a drop in pressure of 5lbs or more will instantly trigger them. I remember the exact spec was in the VDO technical documents I downloaded, but don't remember right now. They also trigger when driven at over 5mph. It's because of this spec that I think the pipe/spare tire method may not reliably work on our cars.

Activating the sensors by letting out air worked when air was let out for 5s. I think air drops at about the same maximum speed it can be put in, which I'm guessing would be about 1lb/sec since it matched the spec for triggering the sensor.

I would like the sensors to allow air pressure of 32psi without triggering. I wonder if I were to teach or relearn the car to sensors with the tires originally filled to 35psi (or less) if I could get the sensors to allow 32psi without triggering the alarm.

[SamirD]

I would like the sensors to allow air pressure of 32psi without triggering. I wonder if I were to teach or relearn the car to sensors with the tires originally filled to 35psi (or less) if I could get the sensors to allow 32psi without triggering the alarm.

Unforutunately this won't work. The tire pressure is irrelevant when learning sensors to the car. It's the pressure drop that's important to trigger the sensors (if you're not using a triggering tool).

So once your sensors are learned to the car, the car receives the pressure data and then decides when to trigger a 'low pressure' warning light.

Just out of curiosity, why are you running 32psi?

[redmed]

Just want a softer ride. Tired of bouncing over these potholes in Michigan.

[~tc~]

Wow, tire wear and mileage trade offs considered, big price to pay for pothole comfort

[bootymac]

What's the recommended pressure anyway? Mine are set to 34 PSI all around from the dealer

[~tc~]

I thought 38 front 39 rear

[Ronzuki]

I'm at 40 right now. What ever the 'recommended' is, I haven't been there since a week or so after I bought the car.

[bootymac]

Just checked the sticker and it's 38PSI all around

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[SamirD]

Just want a softer ride. Tired of bouncing over these potholes in Michigan.

It's the same here in MKE. What size wheels do you have? Once we switched to our 16" snow set from the sport 18s, it really smoothed out. If you don't have a snow set, I'd go with this for a solution as I'm sure the roads get better in the warmer months.

Wow, tire wear and mileage trade offs considered, big price to pay for pothole comfort

And it can be quite dangerous. A certain amount of tire pressure is needed to support the load of the car. If you're under that pressure, you can serious damage a tire to a point where it will fail catestophicly later.

Just checked the sticker and it's 38PSI all around

But this might vary for the various size wheels available for the car. Between the 16s on the S model and the 18s on the Sport GTS/SLS, I'm sure the pressure varies a bit. It can even vary when you replace a tire with a different load rating.

I always use the load rating and max cold inflation pressure as a place to start. If the load rating is 94 and recommended pressures are 40 and max 44, I assume a linear rate for load/psi and calculate the load being supported by the tires. I'll compare this to the GVWR of the car. Then I'll make sure whatever I replace the tires with will have a similar load rating. For our snow set of Altimax Arctics, that means a cold pressure of around the max of 44. It's been hovering around 42-43, so I'm okay with that. But the initial 35psi that the tire place put in didn't cut it at all and you could tell the tires were overloaded (I forgot to tell them the pressure I wanted).

[redmed]

Wow, tire wear and mileage trade offs considered, big price to pay for pothole comfort

You sound like one those congressmen in Washington. If I'm willing to pay for less mileage and more tire wear I want the ability to do just that.