k2kv

I though I saw a post somewhere which explained that you can calibrate the speedo for almost any tire size you want.

Does anyone know if this is true, and how this works?

Thanks!

Jeffrey Behr

.

k2kv

Yep, I thought we all should know!

Anytime...

Roadking

Is this possible? I have 22" TSW wheels on the way with the new Toyo tires. Thanks,

k2kv

So far, the only info I have been able to gather is that the speedo can indeed be calibrated, but you can only select from Porsche's original and optional choices. You cannot just dial in ANY size tire.

Not confirmed, of course.

GM Austin

There is no need to recalibrate with Porsche recommended tire sizes. They are all about 29" in diameter, regardless of wheel size. The selection of tire size in the center display does not change the speedo.

k2kv

A good point. But, what DOES it change then?

JeffES

It changes (in very small increments) PASM settings, the ride height control parameters, brake controller (the system that allows a properly equipped Cayenne to "crawl" downhill), among others. The reason is that a change in wheel means more or less compliance (tire flex) in a given range of wheel travel. A very small change in rolling diameter will have only a very minor impact on the speed/odo readings.
J

Bentley

The size difference is .2". That is not enough to jeopardize accuracy in your speed readings.

k2kv

The original reason for asking was that some of us use (or are considering using) tires which are of non-standard size, such as 30-in diameter, and we wondered if we could accommodate the new size via this adjustment.

Thanks!

Torags

Check your wheel well clearances beforew you take the plunge. Jeffrey has a good feel. I think he has oversized his.

GM Austin

Right. I don't know. It is certainly technically possible. Whether or not the calibration could be achived with this tire selection in the center display, I doubt that will be possible, at least in the near term. But, I do believe it can be done through programming. I just don't think there is any motivation for Porsche to allow, or make available, that capability at present.