ericstanley

I've seen a few track set-ups (mostly a/x) that were 17/17 instead of 18/17 or even 18/18.

Besides the possible weight reduction, what other benefit is there?

dbratten

Availability of tires -- especially nearly new used ones -- at a great cost.

I get Kumho 710 315's and 335's from other racers anywhere from $60-125 each. They're on 17x11" ZR1-GS copies that were also cheap at $130 each delivered from Tomz.

--Dan

ericstanley

So it's not a performance thing, it's a cost thing?

That makes sense... something I'm not entirely used to on CF...

Lancer033

wheels need to be just big enough to fit over the brakes, so if you don't need 18" rotors you don't need 18" wheels - extra weight

tires are cheaper and if you can afford to lose a few tenths, buy scrubs and save a whole lot more. my last set cost $300 shipped.

davidfarmer

I agree with above, BUT when the C5 started racing in T1 in 98-99-2000, the only tires available were 17". I think so many sets of wheels/tires flooded the market, that it just became the norm. I personally run 18" wheels/tires now, and there are plenty of scrubs available (ALL pro series have been running 18's for nearly a decade).

18" rims likely do increase the moment-of-inertia slightly, but I don't honestly consider it a performance issue one way or the other.

John Shiels

17 may make your finale gearing slightly lower because of small diameter but 18's work best.

yakisoba

Weight wasa consideration to me. Also, I was thinking of doing T-1 when I bought wheels, and at the time, those guys were running 17x10 in front and 17x11 in back, generally on racing wheels. Well, the GS wheels are about that (9.5" wide in front, rather than 10") so are pretty close. I figured, if those folks were happy with it, it would be OK for me. The T-1 guys ran either 315 tires all round or 295mm front, 315 rear. I ended up on the latter combination, because it feels better and doesn't warp the sidewalls on my slightly smaller front rims.

That said, NASA rules for TTA dictate that I run a certain size of tire (305mm) in Toyo RA-1 in order to stay within the limits of the class and my car. Those come most commonly in 18", so I got a set of 18s. They also work fine, though I note different braking response and some other minor differences. They have the added bonus that I can swap any wheel to any corner.

The other configuration is to run 17x11 wheels on all four corners. This also allows you to swap to any corner, and allows 315mm tires on all four corners, which is very grippy. I'd think about that configuration for autocross and road courses where I needed massive front grip.

ltborg

+1 for cheaper/more available tires and wheels

ive heard some people say that the 17s are a little more forgiving with the slightly larger sidewall.

some of the advice i got from several people when i was looking at what tires/wheels to get was that with modern tires, the differences are pretty small between the two sizes so unless you are an excellent driver looking for the last tenth or two, its probably a wash. i could be wrong on this and havent done any real testing but thats what i got from the majority of the drivers i asked.

Diesel68

I have used 18 and 17 for the rear, and I found better traction with 17. It doesn't hurt that prices for 17 are also generally lower.

throwit

I agree that 17s are less $$ tires...but I would not go out and invest in a set of 17" wheels (if you dont have them already). Their may be a slight weight savings in the wheel weight (assuming you bought lightweight 17s), but I would think that the larger sidewall tire would negate that.

17s cost just as much as 18" wheels, and do not provide the clearance needed for bigger calipers if/when you decide to do it. Also, a larger sidewall tire (i.e. 35 aspect), while great for rear traction, does not turn as quickly or as crisp as a smaller sidewall tire does (i.e. 30 aspect), and therefore is not an ideal size for up front.

With tires/wheels/brakes only getting bigger I would go with 18s all around, as a safe bet.

FWIW - Popp used to run the 17 rear/18 front combo (which may infact be the ideal setup), but has since switched to 18s all around.

ericstanley

I don't intend to change anytime soon. I was mostly curious as to why others do it.

Thanks for the info. It all makes sense.

Eric

John Shiels

big 18" tires are easier to drive than say my 275 315 x 17's. Little faster but the 17's leave me on edge all the time when pushed hard so it is way more nerve racking keeping things straight..