Bullwings

Not pro or even semi-pro, but diminishing returns for even miatas has yet to be reached. Emilio of 949 racing makes the 6UL in 15x7, 15x8, 15x9, 15x10 - the data and laptimes support that even for a low hp/tq momentum car like the miata (even more so than our s2k), wider is better. If you can fit and clear them, the 15x10s will turn better laptimes.

As far as 17x9 versus 17x10 on 255s, there's a range of rim sizes that a given tire will fit on (which you're well aware of). 255s are better on 17x10s since the lit bit of extra tire stretch (we're not talking hellaflush stretching) maximizes and widens the contact patch a little bit. It also stiffens up the sidewall, which prevents the tire from flexing and rolling, thus maintaining the extra contact patch through the corners (as mentioned by carbonblue).

To the OP: are those volks, RE30? The 17x9.5 +47 option of their TE37s and CE28Ns would have offered BBK clearance, better fender clearance, and a better contact patch for 255s. But, since you already have the wheel, 17x9 +40 is pushing the limits of your fenders quite a bit. You're in the territory where you need a really skilled roller in order to not hellarape your fenders (both from tire contact and/or a poor rolling job).

modMonkey

I don't know the answer to this question either. From what I've read, the general idea is as Carbon Blue stated. The amount of lateral grip gained in corners outweighs whatever you may loose in straights. There's also the idea of better response from a slightly stretched sidewall (255 on a 10" wheel for instance). And of course, most people in the general forum do it for the face. fwiw 17x10 +45 has a concave face, but doesn't clear some BBKs. 17x10 +44 clears BBKs but does not have a concave face.

modMonkey

I was going to reference Emilio stating a 1 second gain for 1 minute on track, for every inch of wheel, but I couldn't find the thread that referenced it. Either way, I also remember reading he has not found the point of diminishing returns.

Yeah, the wheels are RE30s. I couldn't find 17x9.5 +47 CE28 at the time, but I do agree, they should be easier to fit. With the amount of camber I have currently, the setup will clear just fine under most circumstances. The grey area is under full lock + compression.

andrewhake

Moved this discussion to it's own thread to keep this thread on topic.

LickyMYwalker

hey steve! i dont know if that wheel will clear under compression... especially in the front. again though, i dont remember exactly how much your fenders were flared but i dont recall it was that much.

modMonkey

Hey Edwin. Save for aftermarket fenders, how far do people usually have to flare to fit this spec?

Might have to post in the hellaflush thread ...

Sebring AP1

Requires slight pulling. You should be running closer to -3 camber front and rear to be safe.