considering these for my 225TT QC. I have BBS CH in 17x8.5. With the car on Bilstein sports, I'm running 4mm spacers in the front, as the wider wheel at the rim and sidewall "just" clears the strut. I presently have ContiSportContacts in 225-45-17. The wheels are a little wide for them, so the sidewalls are stretched to the bead somewhat.
Stopped by a retail place that actually had some in stock the other day cause I wanted to look at the tread pattern and compare it with the non-A/S, which came on the car. Anyhow, here's the questions:
I'd noted that lots of people on the forum that had bought these indicated that they seemed narrower for the size than the regular PSs. We pulled down a 225-45-17, and a 235-45-18 (all they had) and put them together tread-to-tread. There was NO discernable difference, even tho one was supposed to be 10mm wider. To the eye, center bands to center bands, you could not tell that one was any wider than the other. With that being said and using data from your spec charts, I'm thinking about going with a 245-40-17.
here's the comparison specs
measured section diameter revs/
rim width width mile
PS225/45 7.5 8.8 24.8 837
AS225/45 7.5 8.8 25.1 829
AS235/45 8.0 9.3 25.6 811
AS245/40 8.5 9.9 24.9 834

The 245/40 looks closest to the dimensions on the Pilot Sports that originally came on the car. If they actually measure out smaller, width wise, I can better fit my wheel (8.5), stay wide on the tread, and keep the same overall heighth, which should mean the sidewalls are the same, right?

Do you think there will be a change in the sidewalls relative to the strut on the inside of the rims, necessitating going a slightly wider spacer on the front? I was thinking stepping up to 10s, cause with the 4mm's, it's REALLY close, but not rubbing. I have fender clearance to go another 6mm.
As usual, all info greatly appreciated...
Fig

Keep in mind those specs are taken when mounted on a Rim, and that size rim is called the 'measuring rim'. Despite the tread width, it is the total 'section width' that is important when checking clearances.

I would suspect you may have some rubbing issues with 245/40R17 from the sounds of your specs up there. However, when issues are this tight, the best/only way to tell for sure is an actual test fit.

I don't want to stay with the 225's because my rim is an inch wider, and don't want to go "reality" smaller on tread width if the A/S's are not as wide as the regular PSs. But the 235 45 is .8" taller according to your specs. Prob not a good thing. Hmmmm. The search continues. Guess I'll look up the Nero M&Ss. Are they running truer to size? (I think every forum review I read on the Michelins said go up a size to come out about the same as the original widths)
Fig

I've not heard much about the sizing being off on the Pzero Nero M+S, its so new... I'd suspect they're pretty close to spec in sizing.