Duke, I enjoyed reading your article in the restorer on tire sizes and it hit right on my problem. I have a 67 that I purchased a set of red line Daytona 215/70/15 tires for and put them on a new repro set of bolt on alum wheels. The tires rub on the front fender lip when turning. I had a couple of twist ins in my orig front springs so I replaced them thinking that might help with the rubbing. I gained about an inch in height at the bumper but now the rubbing is worse. Looking at your chart I see that the 205's have an inflated height of 27.1 and the 215's have a height of 27 even. Will the 205's cure my rubbing problem when they are actually .1 inches higher? It looks like I will now have a set of real nice red lines to sell. They cost me $600.00 and they are real good looking but I don't want to buy a new set of 205's and have the same problem. I would like to have red lines but I cannot try them for clearance prior to purchasing. Help!!
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Re: Mid year tire sizes
Dan------
STOCK mid-year Corvettes are very limited with respect to tire size fitment. I was not aware that there was a 70 series tires tire size that would, overall, fit properly.
For a mid-year, I would recommend using 75 series tires. I think that the 205-R75 is about the largest tire that you can use without getting into fitment problems. That's not to say that a slightly larger size might not work on a particular car, but if you're going to buy a set of tires, then you want a set that you KNOW will fit (as you've, unfortunately, found out).
Playing "Russian Roulette" with tires just to achieve fitment of a slightly larger tire size may not be worth it.In Appreciation of John Hinckley -
Re: Mid year tire sizes
I have a better idea. Install the original springs and realign your front suspension. Your car likely has a bit of positive camber now and taking this out or going a bit negative will increase clearance with the fender. My recommendation for C2 front camber is zero to minus one degree and the farther you go in the negative direction, the more clearance you will gain.
Moving your camber one degree in the negative direction from where it is now will move the top of the tire inboard by nearly a quarter of an inch, which should give you some breathing room.
With 215/70R-15s there is the potential for slight interference with the fender lip when the steering wheel is turned to near full lock with jounce, so you still have to be careful entering steep driveways, but you should be able to achieve sufficient clearance for normal street driving with a little negative camber.
Increasing camber in the negative direction will reduce understeer and increase steering response crispness, but it could bias the car to oversteer at the limit. Compensate for this by installing hard urethane bushings on the front anti-roll bar links. By eliminating the compliance of the rubber bushings, the bar will be more effective and increase understeer, particularly at the limit. The combination of a little negative camber and urethane anti-roll bar link bushings will result in a noticeable improvement in handling, particulary steering response crispness. Little tuning tricks like this can significantly improve handling and steering reponse.
You just got a preview of Part II in the next issue of The Corvette Restorer.
In case you're interested in how I made the calculation, I used a basic geometric theory that says the displacement subtended by a small angle is equal to the amount of angle in radians times the radius:
1/360(6.28)(13.5") = .2355"
Of course, the same theory can be applied to the rear, and I recommend about minus one degree camber on the rear.
Be sure you install the original springs before you align as these alignment specs should be applied to the car at normal ride height and curb weight.
DukeComment
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Re: Mid year tire sizes
Dan and Duke-----
I think that the biggest problem of using 70 series tires on a mid-year is not related to the tire diameter-----it's related to the SECTION WIDTH (inflated width of the tire at its widest point). A 7.75 X 15, the bigest tire ever used on a mid-year from the factory, has a section width of 7.70". A 215R70-15 has a section width of about 8.70". That's a big difference. Also, although it varies from tire-to-tire, most 70 series tires have a much wider tread width than the original tires. I think these 2 factors are what causes most of the problems with 70 series tire fitment on a mid yearIn Appreciation of John HinckleyComment
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Re: Mid year tire sizes
Not to mention the fact that the 70 series tires look a bit peculiar compared to the 80 series tires originally supplied with the car. Appearance does play a part in this tire selection process.Comment
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Re: Mid year tire sizes
On a six-inch wide wheel a 215/70 will have a maximum section width of about 8.7" and the thread width will be about 6.5". On a midyear within reasonable body and chassis dimensional tolerance this tire will clear the fender wells on a '67 six-inch rally wheel, which has +0.060" offset, especially if the chassis is tuned with zero to a bit of negative camber up front, but at of near full steering lock there could be some slight interference when the suspension goes into jounce. Thus my caution on entering steep driveways. The 6" wide KO (with adapter) and bolt-on wheels have the same offset dimension, so they are functionally equivalent to the '67 Rally wheel.
This combination of wheel and tire (one make/model in particular) with a little chassis tuning will provide a midyear with very contemporary handling limits and can be installed without any modifications to the car. It's the combination I recommend for maximum driving pleasure if you appreciate sports car handling qualities, and the revs/per mile will not upset your speedometer and odometer calibration.
If your criteria center around other issues, such as duplicating original appearance, then you would probably make another choice, however, it makes sense to have two sets of wheels and tires - one for NCRS judging and shows and another for driving pleasure, if you value driving qualities. In my case driving qualities count 100 percent, so my SWC will NEVER, EVER see a set of 6.70-15 bias ply tires. I got rid of the OEM General Jet-Aires when the car was one year old, and will never install such poor tires again, not even for show!
DukeComment
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Re: Mid year tire sizes
Thank you to all of the great minds who responded. I will have to take some time to think about all of this. I think a little experimenting with the alignment specs is in order before just selling my new set of red lines. If that works I will be one happy guy. Thanks again gentlemen. NCRS is, without a doubt, the best bargain in the universe for a Corvette freak! DANIELComment
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Re: Mid year tire sizes
Agree with Joe. I have 205-75's on my '67, and they fit well, don't rub, look great.
I'm pleased with this choice.
TomComment
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