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: What tire size?


C3Vette
05-10-2004, 06:19 PM
What is the widest tire I can use on a 69 vette with 15x8 rally wheels?
Thanks.

1971bigblock
05-10-2004, 06:57 PM
Originally posted by C3Vette
What is the widest tire I can use on a 69 vette with 15x8 rally wheels?
Thanks.

I have 255 60R 15 on the rear and 235 60r 15 On the front I believe the rears on mine are an 15X8 I don't think you can go much bigger on a stock rim & offset.
JMO

:cheers:

TwinTurbo
05-11-2004, 07:38 AM
275, 295 when you move the parking brake cable bracket.

The pre 78 cars have "smaller" hips than the alter mdoels so wide rear tires will stick out more and can rub the fender edges.

Eddie 70
05-11-2004, 07:56 AM
I have BFG TA Radials on mine. 255/60/15 all around on mine. No rubbing so far.

Fred Mann
05-11-2004, 03:42 PM
Gotta consider getting contact between the tire inside sidewall and the end of the rear spring, if you go too wide. Saw a 70 Vette with 255/50/15 on the rear at an autocross once. Was doing fine until on one turn the end of the spring dug into the tire. Instantaneous deflation. The spring bolt was bent 90 degrees and ripped out a 2" wide section of the sidewall for 300 degrees around the inside of the tire. No exaggeration. I was running the same tires on mine and immediately looked underneath. There were little ruts on the sidewall. I was lucky.

Guldstrand used to sell a steel main leaf replacement that was shorter than stock to prevent this same problem. It stiffened up the spring too. Being into autocross at the time, I got one.

If you run a larger diameter wheel, you might not have to worry about this potential problem.

moore_rb
05-11-2004, 05:01 PM
Here's a pic of my (former) 69. The tire sizes were 255/60-15 front, and 275/60-15 rear on 15x8 rallys:

http://www.digitalcorvettes.com/photopost/data/508/1975Rear-Quarter-med.jpg

I needed to add 1/2" spacers on the rear spring drop bolts (1/2" shorter bolts will work, as well) to prevent rubbing on the inner fender when cutting hard corners.

275/60's work well. I had 275/50's on my 68 roadster, and they gave my grief. Even though the tread width is the same, the lower profile tire's sidewalls "flare" more on a 15x8 rim, which causes rubbing against the e-brake cable, and possibly the spring end mount. I'd suggest the 60 series profile if you want a 275 tread width.

Fred Mann
05-11-2004, 06:21 PM
My first 69 was an F41 car. I had cut half a coil off the front springs for autocross. I had 255/50/15s on the front just as an experiment for a while. The suspension was stiff enough that for the short time I did it, I didn't have a problem. I think tight cornering and some body roll might be a different story. Just speculating. That car also had power steering so the big rubber was ok from that perspective. (I had a 13" wheel and a relief valve in the power steering pump out of a truck for more fluid flow. That car could turn like crazy.)

The 69 that I have now is a standard suspension/manual steering car. I had 245/60/15 in front and 255/60/15s on the back. I like the steering feel of the manual, but if you really have to steer around something quickly you would definitely notice a world of difference compared to a power-steering car. At least with the big block. So when it was time to replace my rear tires, I put the 245s on the back and bought 235/60s for the front. (The 245s were better with the 3.08 rear.) I have really been surprised by the difference that the 10mm reduction made in the steering. Other people that have driven it say the same thing.

So now that I downsized at both the front and rear, I call Guldstrand Motorports about their bumpsteer kit and end up talking to Dick Guldstrand by chance. Among other things, he said that a C3 needed a 255 on the front and a 255 or 265 on the back. (Nice going, Fred.)

If my car had power steering I would go with bigger rubber on the front. For good maximum-effort braking, for one reason. I don't doubt that the e-brake bracket can be a problem. I have read about moving it to the top of the torque arm for just that tire interference problem.

I have taken a grinder and smoothed the sharp edges on the ends of the rear spring, being careful not to let the steel get hot. If the catastrophic tire failure that I'd witnessed at the autocross had happened in the middle of rush hour, things would have been pretty nasty.

Anyway, I guess there are a lot of things to consider in picking rubber for your wheels. Traction, braking, steering, short diameter tires for acceleration, tall ones for top speed, etc. There are even 10" wide rally wheels for more fun.

As usual, I got off the subject some.

Happy motoring!

Flared
05-11-2004, 06:23 PM
ive got 295's on my rears.

C3Vette
05-15-2004, 10:11 AM
I think I'll go with 255/60/15 all the way around. I'm trying to determine the dimensions of the stock tires. I know the designation of the stock tire is F70x15. Does anyone know how to convert F70x15 into a metric tire size such as 255/60/15 ?

Flared
05-15-2004, 12:54 PM
http://www.miata.net/garage/tirecalc.html
this might help.

C3Vette
05-16-2004, 12:16 PM
The size calculator does not recognize the F70x15 specifacation.

:(