Joe Weinstein

This will probably take a real Porsche guru or factory person to answer...

Even the stock front and rear tires on the GT4 are of slightly different
rolling diameters, so I expect the ABS and PASM software would be
tolerant and even adaptive to some difference, so that it would tell
after a few minutes of simple commute-style driving, that the fronts
are turning at XYZ rpm while the rears are a few less or more,and to
adjust to that ratio...

If so, I wonder what the range of adaptability is, and in any case,
what is the allowable difference in front and rear rolling diameters so
the systems don't get messed up?

Could I run a front tire with a diameter 2.2% different than the rear?
Thanks!

ExMB

Are you trying to play with the SCCA class rules to gain an advantage?

Joe Weinstein

I'm trying to play within the rules, yes!

ExMB

Which tires would meet that requirement, 2.2% less, stay within class rules and are sticky enough in OEM sizing?

Joe Weinstein

None that have a recommended rim range that suits our wheel widths...
I am choosing to apply my own more generous range...

Joe Weinstein

Let's find out if this multi-way stretch is even OK with the car systems.
If it is, I'll let you know.

Joe Weinstein

I had a chat with David Donohue, a Porsche racer and rep, and he said this
diff should be fine. The GT4 ClubSport has all the same electronics as the
road car and the race tires they run on those differ in diameter front-to-back
by 6%.

vantage

Good to know, I had wondered this about those running 19" wheels.