C2 tire size

[Barry K.]

ok, ok, I know this issue has been beaten to death on all the various Corvette forums but as I searched I never saw a direct answer for this particular tire size question.

I need to replace my tires on my '65 coupe this winter and I'm currently running 205/75/15 Goodyear Invecta's which were on the car when I bought it. I'm noticing some waviness along the sidewalls and i'm just not at all happy with the performance of the tire. I also get just the slightest amount of rubbing at full turn lock against the frame rail. Just enough rubbing to put a mark on the frame but that's it. I'm assuming the rubbing is because the 75 aspect tire is a bit taller than the standard 70 aspect.

I'd like to run Goodyear Radial GT's in 235/60-15 which my neighbor had on his '67 with no problems.
I currently have the stock steel wheels but also plan on upgrading eventually to the repro bolt-on KO's.
My desire is to have a wider tire for a nicer and "tougher" look to the car and also try to improve the handling a bit but obviously don't want any rubbing issues.

I did a search comparing the standard 205/70-15 against the wider 235/60-15 and came up with these numbers:

205/70-15:
Sidewall: 5.6"
Radius: 13.1"
Diameter: 26.3"
Circumf.: 82.6"

235/60-15:
Sidewall: 5.6"
Radius: 13.1"
Diameter: 26.1"
Circumf.: 82.0"

Between the two sizes, the sidewall and radius compare as the same, and the 235 tire has just slighter smaller diameter and circumferance. Based on that, i'm figuring it should fill up the wheelwell almost as much and should also eliminate the slight rubbing i'm getting on the front frame rails but not create rubbing elsewhere and will give me the wider look i'm trying to obtain.

Any comments?
Anyone else running 235/60-15's that can comment or say if my calulations are off?

if I really need to I could drop down to a 225/60-15 but a lot of this choice was based on the looks and the fact that there were no rubbing issues at all with the 235 tire on my neighbors car.

thanks for your help.

Barry

[Joe C.]

Re: C2 tire size

Barry,

If you check the archives, you will find much info on this subject, particularly if you look for Duke Williams's posts.
You will see that a 215/70R-15 will work as well as a 205/75R-15, but with larger footprint.
I have seen some midyears with 225/65R-15's as well, but never bothered to check the vital statistics.
I would suspect whether any 60 or 65 series tire will fit on a midyear without rubbing during full lock turns with jounce.
Are you certain that your friend's car does not have the inner sections of the wheel lips removed?

Joe

[Barry K.]

Re: C2 tire size

Joe

yes, I know that most people seem to recommend staying with the 205 - 215 range which is why i was very surprised when I saw my neighbor running the 235/60-15's with no problems at all.
His car is 100% stock with no modifications at all to the fenders, lips, etc and he is running the stock trailing arms - not offsets.

[Paul L.]

Re: C2 tire size

Barry,
We hang out in the same neighbourhoods! But with the wider 60 series tire you are basically just dropping the edge below the lip-line of the fender (watch big bumps), and outside, and leaving a lot of unsightly space. That space was formerly taken up by the 70, tucked neatly inside the fender lip. It's all a matter of taste of course and I need not reiterate mine. BTW, winter storage day tomorrow. I sat beside the 1967 in the garage tonight, gave it one last swipe with the California duster, and soaked up a few cool ones. Another driving season gone.

[Barry K.]

Re: C2 tire size

Paul

on my neighbors '67 with the 235/60's it definately wasn't sticking out past the fender at all. It didn't fill up inside the wheelwells as much as a 70's series tire of course but it wasn't sticking out beyond the lip. In fact I remember I could just put my finger inbetween the lip and the tire so there was a small amout of space there so rubbing the fender lip shouldn't be a problem from what I saw at least on the rears. He said he had no rubbing at all in the front either even on full turn lock but that is really my biggest concern and why i'm asking for other opinions rather than just running out and ordering the tires first.

We hang out in the same neighborhoods? where are you from?

[Joe C.]

Section Width Is The Key..........

.......to rub problems in most cases, especially in the frame rail areas. Since there is very little margin of error in "midyear"
tire sizing, AFA clearance issues are concerned, then the best way to check clearance issues, is empirically. Borrow your friends tires/rims and take your car out for a blast......push the envelope and check for problems. There is nobody that will tell you , FOR SURE, what will fit and what won't. Why? Because there are variations from car-to-car that make the nominal "margin of error" moot in the case of tires.
Use Duke's suggestions and/or those provided in most tire store specifications sheets to deduce correct tire circumference values.

Joe

[Paul L.]

Re: C2 tire size

Barry,
Virtual on-line Corvette neighbourhoods (e.g. paul67).

[Barry K.]

Re: Section Width Is The Key..........

Joe

John Hinkley just replied to me regarding this over on CAC and mentioned what I hadn't thought about...... the 235's won't even fit on my wheels. They require a minimum of a 6 1/2" width wheel and recommend a 7 1/2" for best performance while my stock '65 wheels are only a 5 1/2" width. I forgot to take into consideration this fact and that my neighbors '67 has the wider rally wheels.
this is disappointing as his car looks great with those tires on it.
oh well.......... back to the research for a different tire size.
i'd REALLY like to go as wide as I can but obviously do not want any rubbing or hitting issues, especially on the fenders since i waited almost 11 months to get the car back from the body/paint shop from getting the body redone and brand new paint.

thanks everyone for your replies and input. I guess this thread is finished.

[Tom B.]

Re: Section Width Is The Key..........

Barry,

Check out the tire size calculators that are on most tire brands web sites. There are several in the toolbox on the CAC. They not only give all the vital statistics on the tires but list the rim width range and the design rim width for the tire. This will at least show you what you can consider for your stock wheels.

Tom

[Barry K.]

Re: Section Width Is The Key..........

Thanks Tom

i've gone back and done that. The first time I did it the "tire calulator" i used didn't give the section width info or the wheel width requirements so that's what threw me off and I was thinking the 235's will work.
Once this was brought to my attention I did another achive search and also found another tire calulator to use.
looks like on my stock wheels the recommended 215/70-15's are going to be my best bet. I really wanted to go a bit wider, but really can't on stock wheels and without risking my bodywork and new paint so I'll live with that size.
Oh well, life is all about compromises!

[Joe C.]

Re: Section Width Is The Key..........

Barry:

Just a few followups:

First, when tire manufacturers specify minimum rim widths, they are of course "covering their butts" by being extra conservative. You can probably use a 1" narrower rim safely. You will probably never drive your car at the limits, and so will not need the extra safety factor. I have done this a few times over the years, and have yet to have an incident. I am only suggesting that this is POSSIBLE, and if you decide to try, then you will be doing it at your own risk.

Second, the seventy series tire already has a higher ratio of width-to-height than the 7.75 - 15 bias ply tires that were originally installed on the car. The first replacements were the old "78" aspect ratio tires, superceded by the current "75" series. I am guessing that the original 7.75 - 15 tires probably had an aspect ratio somewhere between 80 and 90. So, you ARE making an improvement by mounting 215/70's.

Third, you MIGHT want to look at the Pirelli P4000E in 225/65 - 15. I haven't looked at the vital specs (i.e. revs/mile and min rim width) but you should. As I said, I have seen more than a few "midyears" with 65 series tires mounted to original rims. The brief conversations with the owners suggested no clearance issues.

Joe

[Joe C.]

More

I just re-read your original post, and noted that your 75 series tires rub the frame rails. If you use any tire with wider section width than 75 series, you will only exacerbate the problem. I would have to say that your situation is unusual. You might have to extend the steering limiter tabs on the rails in order to limit full-lock travel of the tires. The new knockoffs that you plan on buying are 1/2" wider than the steel wheels, at 6" wide.

Joe

[Barry K.]

Re: More

Joe

on another thread on here i read that someone else also just put 205/75-15's on their car and it's rubbing also so it's not just my car doing it.
i think the taller 75 series is at least partially to blame rather than the more recommended 70 series.