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I replaced 15 inch 255/60/15 T Rated tires on my 78 L-82 gymkhana suspended car (lots of upgrades over the Sport factory Suspension) with 255/45/17 Z rated ultra high performance summer only tires and the difference in ride, handling, and steering response is very noticeable. I made no other changes to the suspension when I added the tires. One of the best upgrades you can do to your car. A 17 inch Z rated tire (W/Y sub rating) has much softer grippier rubber, a much stiffer sidewall, and much less tread squirm that a lower rated tire like the mass market 15's. You will notice much better braking in the wet and dry, better steering response since the sidewall and whole tire carcass is much stronger, and believe it or not, a much better ride. You win all around...the downside is that Z rated tires generally will wear faster, but I have never worn out a set of these type of tires since I don't drive the 78 enough to accumulate high mileage. !7 inch sizes though will eventually go the limited selection of 15's......
As you can see the selection of 15's are getting very limited. The rubber compounds are also "basic" in the limited street tire offerings.
The combination of a shorter much more stable sidewall and modern compounds make for a substantial handling improvement.
..17 options are even going to fall away eventually as the 15s (and 16s) did. Going to an 18 will put you that much further ahead.
C3's came with approx. 27 inch tall tires. These properly fill the wheel wells. The popular 255R45 17 are about an inch short, and going to a lower profile only makes the problem worse.
Other miscellaneous thoughts;
1) The lower profile and performance design of 17/18 inch rubber will
will greatly improve the handling of your car, giving it a sharpness it never had before.
2) I also went with offset upper A arms to get me more caster. It improved straight line stability greatly.
Last edited by Rotonda; 07-25-2016 at 06:35 AM.
Reason: addition
C3's came with approx. 27 inch tall tires. These properly fill the wheel wells. The popular 255R45 17 are about an inch short, and going to a lower profile only makes the problem worse.
Other miscellaneous thoughts;
1) The lower profile and performance design of 17/18 inch rubber will
will greatly improve the handling of your car, giving it a sharpness it never had before.
2) I also went with offset upper A arms to get me more caster. It improved straight line stability greatly.
Correct on all points!
The 255/45/17 is apprx 26 inches in diameter. The same overall diameter tire as the 255/60/15 (27 inches) is the 255/50/17 which is also 27 inches in overall diameter. I actually have 255/45/17's in front and 255/50/17's in the rear since I did not want to go to a smaller diameter tire with 3.70 gears which would have raised the rev's even higher on the highway than they already are.....and the lowered front stance actually looks more appropriate for these cars than the rear droop common on C3's. Different diameter tires front to rear is very common on modern cars, especially sports cars and sport sedans.
The 255/45/17 is apprx 26 inches in diameter. The same overall diameter tire as the 255/60/15 (27 inches) is the 255/50/17 which is also 27 inches in overall diameter. I actually have 255/45/17's in front and 255/50/17's in the rear since I did not want to go to a smaller diameter tire with 3.70 gears which would have raised the rev's even higher on the highway than they already are.....and the lowered front stance actually looks more appropriate for these cars than the rear droop common on C3's. Different diameter tires front to rear is very common on modern cars, especially sports cars and sport sedans.
I took 17" off one of my cars and put 15" on. The ride is much better. I am not making any claims about handling, as in Autocross. I only drive on the street.
Last year I put on 245-50-17 (26.7") mainly due to no choices in 15" tires.
I chose Michelin as I had the same Michelin's on my other car as was very satisfied with their performance.
On the vette, I went from Goodyear Eagle GT, 245-60-15 to the Michelins.
Incredible improvement in regular driving, I have manual steering, and it was like adding power steering.
Cornering was much improved. (Much reduced sidewall flex)
Tire road noise reduced at least 80%.
On large bumps the ride was a little harsher, however small bumps and regular driving was improved.
Overall, very pleased, I would never go back to 15" tires.
[QUOTE=ddawson;1592704379]18 here. Night and Day difference with a Max Summer Tire.
Absolutely right! Potenza RE-11s summer only here. Super stiff sidewalls. 275/40/18 in back and 245/45/18 up front provide a lot of stick to the ground. I don't have to slow down for corners anymore.
I cut a coil off my 460lb springs with Bilstein shocks up front for an effective spring rate of about 520lbs, and a composite rear that measure at 340lbs with Konis in back. Add spreader bar and heim joint rear camber arms and we still have a surprisingly comfy ride.
6.5* of caster with the tubular upper control arms really helps firm up the highway speed steering. Finally finished the third and final phase of suspension upgrades...yeehawww.
I took 17" off one of my cars and put 15" on. The ride is much better. I am not making any claims about handling, as in Autocross. I only drive on the street.
Is it possible your maybe an older gentleman who also doesnt care for the look?
The only way This makes any logical sense is if either the 17" tires had something wrong with them or you were trying to make the car ride softer and less like a performance / sportscar. The larger sidewalls can give you a softer ride for the same reasons they dont handle well. theres more cushion and flex. in any case most considering them on a corvette would like better handling I'm guessing.I'm not trying to be a wiseguy here and I realize we all use our cars differently and if its just for cruising with the Mrs and you want it to ride more like a Buick then the 15s would have the advantage.
I just went from 15" tires to 18" 2 weeks ago on my 74 and the handling improved quite a bit. The car feels much better when cornering and is just more responsive to road conditions/ feel.
Last edited by augiedoggy; 07-25-2016 at 10:07 PM.
I went to Cooper Zeon RS3-A 255/50 R17's on all 4 corners and what a difference.
I have Kuhmo ECSTA SPT 17's on my 78..Max Performance summer only and love them but I have had many sets (4 or 5) of the Cooper Zeon RS3-A's on my DD's (245/55/18-Chrysler 300 and 225/55/16 on 2001 Grand Prix) and they are awesome and one of the best deals out there for ultra high performance tires all seasons. Excellent grip, wet or dry, very good grip in cold temps, and very good mileage for a ZR tire..I get about 40,000 miles out of a set. I just bought a set of Cooper Zeon RS3-S (summer only) ultra high performance for my Mustang GT convertible but have not mounted them yet but expecting max performance from these tires...Just an FYI..Great tires for the money!
I went straight to 18's and couldn't be happier with the handling and ride quality.
Front: 18x8.5
MICHELIN PILOT SPORT A/S 3
255/45ZR18
Rear: 18x9.5
MICHELIN PILOT SPORT A/S 3
285/40ZR18
Overall height is near perfect to stock.
They ain't cheap but damn do they stick!
Michelins Pilot SS's are the best you can buy!!!
BUT like everything in life, you get what you pay for....Coopers are NOT Michelin Pilot SS but Coopers are much more affordable and pretty good. Eyeing the Michelin Pilot SS's for my C6Z06......especially since the Z06 is going to be a track car once ClubMotorsports completes their road course track not too far from me this October 2016 where I am a founding member (joined 12 years ago...long wait....)
Is it possible your maybe an older gentleman who also doesnt care for the look?
The only way This makes any logical sense is if either the 17" tires had something wrong with them or you were trying to make the car ride softer and less like a performance / sportscar. The larger sidewalls can give you a softer ride for the same reasons they dont handle well. theres more cushion and flex. in any case most considering them on a corvette would like better handling I'm guessing.I'm not trying to be a wiseguy here and I realize we all use our cars differently and if its just for cruising with the Mrs and you want it to ride more like a Buick then the 15s would have the advantage.
I just went from 15" tires to 18" 2 weeks ago on my 74 and the handling improved quite a bit. The car feels much better when cornering and is just more responsive to road conditions/ feel.
I didn't like the way the 2" hard sidewalls jolted the car with every bump. The 9 1/2" width also caused issues with rubbing at inopportune times during sharp turns on uneven roads. I changed for four reasons:
Ride is less harsh
Rubbing fenders in some situations
I wanted the stock rally wheel look
Previous owner wanted to buy wheels and tires for more than I spent on the changeover
I suppose age is a possible fifth reason, since I dislike vintage cars with 19, 20 inch chrome wheels with short tire sidewalls that all you young fellers spend so much on. I'm a stock wheel, or at least period style wheel kind of person. I also don't like the big chrome wheels that continue to spin after you stop, or the black wheels that look like wearing black socks and shoes while wearing a bathing suit. If we all liked the same thing, a lot of vendors would be out of business and all cars would look the same (which may be the way we're headed anyway with wheels)
07-25-2016, 12:14 AM
Will going to 17 inch wheels help handling?
