Appraiser

Hi all,

I hate to ask something that's been answered before but my google-fu and search skills are letting me down, I can't find a straight answer. I've got an '07 C2 base stripper with 18" diameter wheels.

My rear Potenza RE050's are nearing the end of their lives after Monday's DE and I'm looking for a minor size upgrade while I'm at it. Currently my C2 has the stock 235/40R18 in front and 265/40R18 in the rear - guys at the track suggested 295 in the rear but that sounds like a big bump in size... I had no problem with the 235/265 setup at Chuckwalla - I thought there was plenty of grip to play with but maybe that's the Potenza's talking, anyways I suppose a small bump up wouldn't hurt, right?

What are some size recommendations for an 18" factory C2 wheel (18x8 and 18x10)? I'm also lost on which aspect ratio to choose and why - I understand it's the "height" of the tire and to keep it proportionate but I'm not understanding the principle behind why it would change (35 & 30) with a larger section width... I'd assume you'd want to keep it the same at 40 front and back or 35 front and back, etc. Why would it be staggered?

Could I do 245/35R18 front and 285/35R18 rear Potenza S-04 Pole Positions for instance? Or keep the aspect ratio to the original 40 and do a one size wider setup like 245/40R18 front and 275/40R18 G-Force Sport Comp-2 set?

Cheers!
Colin

Hella-Buggin'

Lots of great options and those can be narrowed down based on how you use the car.

Daily driver?
Weekend back roads?
Autocross?
HPDE?
All of the above?
climate conditions?

are you a cruiser or do you get on it in the twists and turns?

if you're looking for a tire that will do all of that? Reports on the new Michelin Pilot Sport 4 ( I think) are probably you're best bet. They're not out yet but should drop in the next few months.

Appraiser

Hi Hella - thanks for posting.

50/50 between HPDE and scenic drives. No DD duties and no autocross. I heard RE11's are a popular choice but I thought my RE050's had lots of stick at Chukwalla given my (lack) of skill and would like to stay around that performance category. Admittedly I'm gun shy to anything significantly stickier - I liked being on or near the limit and am comfortable at the speeds I was at, at least for this year!

I'm still lost on aspect ratio and good possible sizes for the standard C2 geometry outside the 235 & 265/40R18 default. Plus there seems to be more tire choice by changing the sizes, at better deals too.

America's Tires is running a presidents day weekend promo and I'd like to buy a set this weekend. Potenza S-04 Pole Positions in 235 & 265/40R18 will run about $772 installed after $100 rebate. But if I increase the section width a little a set of Hankook V12 Evo2's in 245 & 275/40R18 would be $681 installed after $100 rebate. I think these tires are comparable to the RE050, right?

I'm still lost on the benefits of changing the aspect ratio. Is there some sort of technical cross reference chart for best fitment to wheel size? By going with a "shorter" sidewall/tire I'd be increasing acceleration but losing top speed, and my speedometer would need a correction, right? I'm using bicycle gears illustrations in my head to rationalize that! Now why mix-match the aspect ratios, if the front is shorter, would that mean less sidewall real estate for more direct turn-in - and retaining the rear height for overall top speed? Is there no negative detriment to having two different rotating speeds to the balance of the car? Also wouldn't there be more contact on a larger sidewall tire with the same cross section width... does that play into the equation of choosing mix-match aspect ratios? Is it a camber degree issue?

And while we're at it, is there any purpose to adding Porsche spacers for a C2 besides aesthetics? I think my factory offset is 57 & 58 mm front and rear...

Appraiser

Just to throw it out there I ran some price matrices on what I think could be appropriate fits.

Bridgestone Potenza S-04 Pole Position in 245/40R18 and 275/35R18 $788 installed after rebate.

Hankoock V12 Evo2 in 245/40R18 and 275/40R18 $707 installed after rebate.

BFGoodrich G-Force Sport Comp 2 in 245/40R18 and 275/35R18 $655 installed after rebate.

For the money the G-Force Sport Comp 2's sound like a good deal, I'm unsure if they are comparable to the other two.

The V12's don't come in any other 275 sidewall size than 40, so maybe that solves the dilemma, eh?

ATSR

I suggest you play around with different tire sizes in the following website:

http://www.willtheyfit.com