RJay

Been many years since last I posted here. I thought perhaps others might have thought this approach through already so I figure I'd pose a few questions. Searched the forum, didnt run across anything relevant.

First background. I'm currently looking at buying some form of Cayman. It will serve as primarily as a daily driver, but also as an AX car for teaching my son how to drive. Ive owned a pair of 911s for many years, 1970 and a 2000 Brumos special edition so I have more than few extra sets of wheels around. First question, is the bolt spacing/ hub diameter/offset still the same or has it changed somewhere along the line? ie. will my old wheels mount properly?

Now for something a little more complicated. A general complaint, I share, is that the lower gears are way too tall in the 718. Those with a bit of history with the marque (and a garage full of extra rims) might recall that back at the turn of the century both the Boxster and 911 were running 225/40/18F, 265/35/18R as opposed to the current 235/45/18F, 265/45/18R. So by the tire calculators, the 718 has a diameter of 26.3"F, 27.4"R whereas the old lower profile tires yield 25.1"F, 25.3"R. I've always run 285/35 rears on the 996 which yields 25.9". Wouldn't quite preserve the rake of the 718, but it gets it closer. I'm assuming fitting 285s back there is not a problem, anyone know?

Hopefully by now you see where I'm going with this. Assuming I can mount other wheels in my collection with lower profile rubber, I wind up with lighter wheels/lighter lower profile tires which equals shorter gearing, stiffer side walls and better overall performance. Of course there are several downsides. Can't hit 170MPH any more. I'm good with that. The more relevant issue is speedo error. With around 5% with 285s, you're looking at 80MPH indicated being an actual 75.6 (assuming speed is calculated by a tranny, diff or rear wheel sensor... dunno). Is there any way to reprogram the speedo ratio? That said, while it would be nice to fix this, but I certainly could live with the error. An extra 500 mile indicated every 10K shouldn't kill resale too much.

The more critical area of concern is ride height. I've already read in reports of cars occasionally scraping on the SPASM suspension. I'd like a car with the e-dampers, but not if they preclude the above, which from the numbers I'm guessing they might. I suppose a set of springs, even custom ones, are pretty cheap, but at some point one starts getting into too many issues for such things to be worthwhile on a daily driver. By my calculation, the drops from the tire changes are 15mm F, 19mm R, so on a stock suspension car, essentially you wind up at spasm heights. I'm guessing that lowering a SPASM equipped car a further 20mm is undoable. With a PASM one, it seems risky, but it might work.

Certainly if I was tracking the car, this is the first mod I'd make. It's certainly the cheapest fix for lowering the gearing, reduces the unsprung weight and has the added benefit of cheaper and more plentiful tire choices. Given the benefits, I doubt I'm the first one to consider this. So I'm wondering if anyone around here came to a similar conclusion, gave this a try and if so how it worked out.

mrrippey

I’m running 245/35-20 front and 275/35-20 rear

Rippey

RJay

Well, the die is cast at this point. Bought an '17 S today with 20" S wheels and SPASM. Too good a deal to pass up. Did find out that the while the bolt pattern is the same, the offsets have changed, so we live with with the 20s.