I just recently purchased my first Corvette, a 65 Coupe. The previous owner put 205-70R15 radials on the car. I'm interested in keeping radials, because its going to be a driver. The tires don't look right on the car to me, they just look to small. I've checked dimensions of different sizes compared to the original 775-15 bias ply. Most tire comparison guides indicate that 215-70R15(diameter=26.85") are the radial replacement for the 775-15's (diameter=27.61"). It appears to me that it would take a 215-75R15 (diameter=27.70") or a 225-70R15 (diameter=27.40") to closer match the diameter of the original 775-15 tires. I'm sure that a lot of owner's have installed various sizes. Does anyone have good experience with installing 225-70R15's, any rubbing problems?
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Re: C2 Equivalent Radial Sizes for 775-15
Don't compare diameters. Compare specified revs per mile, which are 775 for the OEM 7.75-15. Revs per mile and wheel width range for each size are usually specified on manufacturer's web sites and on The Tire Rack for each tire under "specs".
The 215/70R-15 is also 775 or very near and there are a couple of V-rated models in this size on the market. They will fit on the OEM 5.5" wheels, but 6" Rally wheels are a better width, and they will accept previous model wheel covers.
The 225/70R-15 is too narrow for a 5.5" wheel, and marginal on a 6" wheel. It is speced at 760 revs/mile, equal to 6.70-15s, but whether it will fit without clearance problems comes down to a case by case basis.
The best wheel/tire combo on a midyear is the 215/70R-15 on a six inch wheel, either KOs, bolt-ons, or 6' Rally wheels with the trim rings or wheel covers.
Duke -
Re: C2 Equivalent Radial Sizes for 775-15
What are the revs per mile on a 205/75x15 Michelin? I would think this would represent a better choice since it's aspect ratio of .75 is closer to the original's aspect ratio of .80. Certainly the outward appearance would be closer to the original. The mathematical conversion of the cross sectional width of 7.75 in is 197mm. The closest nominal cross section would be a 205 since one is forced to use a 75 ratio tire instead of a 80 ratio like the original. Hence, the conclusion that the 205/75x15 might represent the better solution. The unknown is the revs per mile on this tire. If I could get that nailed down I think this discussion would conclude with a suitable answer. My concerns with the 215/70x15 are that the tire's outward appearance is significantly altered from the original and that there might be the chance for a physical interference with the front fender lip when pulling into an inclined turn at some slower speeds.Comment
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Re: C2 Equivalent Radial Sizes for 775-15
The Michelin web site or The Tire Rack site should list the revs/per mile for the specific 205/75R-15 Michelin you are referring to, and it will likely be very close to 766 revs/mi.
The problem with 205/75s is that they are, based on my research, all very hard compound (wear rating 400 or more) generic all season tires with speed ratings no better than "S", so they are not what I consider "sports car tires", but they are adequate if you drive your car easy and don't demand sport cars performance.
Michelin offers the V-rated Energy MXV4 in the 215/70R-15 size, and Pirelli offers the P4000 Super Touring in this size, which generated impressive skidpad numbers on a vintage Maserati Ghibli that was tested along with the new Maserati coupe in the Novmeber Car and Driver.
I have not heard of any severe fender clearance issues with a 215/70s on 6" Rallys, bolt-ons, or KOs on a midyear, but they will potentially interfere if the suspension goes into jounce with significant steering lock, so you have to be careful entering steep driveway approaches at an angle. I'm well versed in this drill being as how I run 225/70VR-15s on '68 7" Rallys on my SWC. I trimmed the fender lips when I first installed the wheels back in '68 with 205HR-15 Pirelli Cinturatos, and I don't plan on restoring them back to original, but I would not do this today, nor do I recommend it.
Duke
DukeComment
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Re: C2 Equivalent Radial Sizes for 775-15
In '68, my buddy traded in his '66 roadster (worst move I ever saw anyone make), but he sold me the '68 rims with 205-15 Pirellis and I put them on my SWC. I had to do the same rear fender lip trim. Fortunately, I still have the SWC, the '68 rims, two of the Pirellis (shot, but seem to hold air), and the original '63 rims. I think I'm going with the 205-75's on the 5-1/2 rims. I have no desire to reenact the insanity of my youth- even had the base engine rebuilt all original- cam, WCFB, stamped valve covers, the works.Comment
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