Well I thought I was gonna be okay with my 17" TTII's on and toyo t1-s from my 15 inch stock rims.
But then I was talking to one of our consultants at work who also races open wheels and has 3 teams. He was telling me that by going to the 17 I could actually be hurting performance by throwing of the geometry that the car was originally designed to have with the 15 inch wheels. He's quite knowledgeable and I am just asking others opinions. He says that I will be better off with a 15 inch wheel and super sticky tires for performance and handling, since that is what the car was made for.

 

I'm not sure how wheel size would change geometry?

-Chris

 

Having gone from 15" to 17" I can tell you there's no going back. Handling is much better with the shorter sidewall. I also like the ride better as the 15"s hade so much sidewall it would wallow.

 

hmmm it's a tough debate for me, is there a 15 inch tire out there, maybe a mickey thompson or something with a super hard sidewall? hmmmmm :boxing

 

maybe i should just keep the 17's on for daily driving and road racing and put the 15's on for drag racing at the track........ :banghead:

 

Ditto Zwede on performance of 17s.

If you go to 17s with tires of much different diameter than OE, you will change the geometry. Otherwise, I don't agree with your friend.

 

can i go wider than 255's in the back w/o changing the trailing arms?

 

You might have to relocate the parking brake and shorten the end of the rear spring. I have 255's and stock TA's and I can't see going much wider without these changes.

 

Ditto Smokehouse. I had exactly this situation before changing to 17s.

 

i disagree with your friend. i'm sure he means well, but his statement is false to begin with. the c-3 wasn't designed for 15" wheels, it was designed to perform as best it could within the limits of 15" wheels. i'll echo everyone else here about the handling performance of 17s. especially on a street driven car, it will yield the single biggest handling improvement you will see, with minimal compromises too.
i can understand the idea behind 15s for drag slicks where you want some sidewall deflection, yada, yada, yada. but for 'spirited driving', the new tire technology is far superior to anything you'll find available for a 15" short of a full blown racing slick.
additionally, to answer your other question. the tires on my car in the sig pic below are 285/35ZR-17. i have done no modifications to the T/A or the spring and have no problems other than the e-brake bracket hit a wheel weight, but otherwise does not contact the wheel. most seem to require the bracket to be relocated.
i think the 285 will be as wide or wider than you want to go. with -1* rear camber, the outer edge is about 1/4" past the wheel well. when i mount a 275 on it, it's just about dead even. personally, i like the look of the tire being right on the ragged edge of the body line so it works for me but some don't.


[Modified by clutchdust, 10:05 PM 9/11/2003]

 

I'll go up in rim size when I need new tires- the options in a 15" tire are very limited these days in terms of speed rating. The compounds & construction are far better in the larger diameters.

 

:skep: really...

where does this guy find performance tires for 15" wheels (other than R25A racing slicks)


[Modified by Turbo-Jet, 2:14 AM 9/12/2003]

 

I both agree and disagree with the friend there....lemme esplain....

As some of you all know, I have 17" wheels from a '92 vette on my '72 shark...with 2.5 inch VBP wheel adaptors....and it's about the second biggest improvement to the car I ever made...first being DPFI....
third being the Rack/pinion install....

OK, NOW having said that it seems like I"m against his friend....the disagree part.....

BUT, in the long discussions with Norval, and Pete79L82 over the last few months starting with r/p installs and ending up about much further suspension mods....so it seems the smart guys are discovering the limitations imposed on the late 50's design of the shark chassis was a result of the crappy tires at the time, the front end geometry actually allows the TOP of the outer front tire to move OUTWARD in a turn, tilting the tire so the tread rolls out enough to balance the rear....BUT with modern tires this is not a good condition, especially with lo sidewalls, SO we need taller spindles apparently to lower the roll center, and make the top of the tire lean IN in the turns....this plants the tire tread more frimly, and it still stays on the rim due to less tire wall height, cant roll off....and the rear is more sticky too, so it will not swing around so fast...

SO apparently, from what I understand, the racer friend mentioned above is correct, but not entirely.....

note the choice of words there......in the description of the original design...

GENE

 

I could not believe the difference in handling of my car when stepping up to the 17's. If there is someone locally who could let you borrow their wheels for a short drive, you'll instantly converted to the benefits of larger wheels. With the Z rated wheels, my car sticks so much better when autocrossed over the 15's that were new & still POS's ;) .

 

OH, YES, no question about it, BUT our cars need another mod so they can 'bee all they can be'......

GENE

 

:bs This makes no sense to me. If it were true, are you racing your C-3 on an oval at a professional level needing to shave some fraction of a second off your time? There is no way a 15" set up could come close to the 17" set up in terms of handling. I've also noticed that while it was easy to break loose the 15's in a straight line, the 17's are like glue. Still, I could see a 15" drag tire being better off the line, but I can't buy the geometry/handling comment. :skep:

 

I have no knowledge of performance and handling but 17" looks better :thumbs:

 

Well gonna throw in my 2 cents.

I went to 17s..and there is a BIG difference in the handling!! I also lowered my Vette on the front by 2 inches...and THAT made an even BIGGER difference.
NO way I would go back to 15s.

 

After reading all the replies, my 2 cents: Your friend assumed the overall diameter will either increase or decrease to the original tire/wheel combo. Thas is not necessarily true..see, you can maintain your original diameter by selecting the correct tire profile/width combo. I can't remember what our C3's diameter is, 26.5" or 27"...just select a 17 tire with that diameter, or as close to it as possible. The tire performance in the 17" category is worlds appart from the 15"'s...they corner better, have a higher speed rating, you can get all weather performance, the options are endless.

 

Stock tire height is 27" 225/70/15 255/60/15.
255/50VR17 is correct height.
FYI, Handling can be very good w/ FE-7 & 15s.