Is it stupid to run 19's (with PASM) at a short, technical track? Would I be better off reducing weight and getting 18's? (I'm not sure 17's work with the 987/997 PASM-equipped cars or not, but the wheel wells are pretty darn huge so I would think that it would look odd)

 

Track tires for 18's will certainly be cheaper, lighter, and more sizes are readily available.

So, it might make sense to move to 18's. However, I do not know how sensitive the PASM system is to wheel diameter and weight changes.

 

you can always have the wheel O/D reprogrammed at the dealer, but that lends itself to be a hassle after awhile. Haven't checked the usual suspects, but any idea if new options are available for those of us w/ 19"s outside of the michelins?

 

- Does the dealer have to program wheel diameter into the system?

- Are aftermaket wheels an option for PASM equiped car owners?

- Will switching wheel size/weight/offset ruin the system benefits?

Just curious as I do not totally understand this system....

 

Those are all good questions that I'd like to know the answers to also.

 

I have never heard of the dealer programming the diameter into the system, so i am not sure if this is possible or recommended, sounds wrong to me though.

Again I am not absolutely sure, but PASM shouldnt really be affected by a change in overall diameter as it is only the system of active dampers on each wheel.
I am sure it talks with the PSM for speed and hence grip conditions at each wheel so it may be affected a little by radically different sizes.

The weight difference probably wont be a big problem, unless you are going with some huge chrome spinners or something, because the 19"s and 18"s are both offered from the factory and have different weights.
Of course more weight is detrimental for performance though.

The PSM system will of course be much more susceptible to problems.
I have heard from some Porsche tech persons that any change within 5% of factory should be ok.

Just go with sizes that are close to standard and you will be ok.
We had a discussion earlier on the options available fot he 987 which you might be able to find a little down this board. They were mostly for 18"s though.
Some are running different size tires already with no problems.

 

I'm not so sure the dealer would actually plug in the O/D of the tire, but I would venture to say that part of the unit configuration would be known defaults (i.e. 18" defaults, 19" defaults) to let the 1) speedometer and 2) traction control system know whether or not the car is performing within specs. This is the case for many vehicles with stability/traction control and I would be surprised if Porsche didn't have something very similar.

I can only offer a 'for instance' .. for instance, when I had 18" wheels added to another european vehicle of recent vintage, beyond bolting the wheels to the car, the car's computer had to be "told" it had the new wheels, for all of the items described above. As I had OEM wheels (not aftermarket) there were no negative effects. I wouldn't assume that any of these onboard systems have the level of granularity that would allow an operator to enter the actual O/D.