Oh no! More C2 tire questions

[Doug L.]

Hi everyone,
I have read threads about C2 tires and wheels until my head spins. My car is a '64. I now have correct 5-1/2 x 15 wheels with 6.70 x 15 repro BFG Silvertowns for judging.

The wheels that were on the car when I bought it were incorrect for a '64 and had F78-15 bias tires on them. Upon removing those tires this week I found that the wheels are probably 65-66 wheels as they do not have the cone-shaped rims and they are stamped 15x5-1/2 JK (some replied to a previous thread that they may be "8080" service replacement wheels but I think the "JK" indicates OE wheels).

Since this second set of wheels are 15x5-1/2 I am considering mounting radials on them for normal driving after removing the correct wheels after judging. I have 2 fears: 1) These wheels with the F78 (7.75) tires mounted were within 1/16" of rubbing against the axle snuber bracket that protrudes slightly from the frame sides, and 2) A previous owner cut away the lip of the wheel wells (which have now been restored) presumably because the F78s rubbed. The body is off the car at this time so I can't check this theory.

I read in this forum that the offset of the correct 64 wheel and the OE 65-66 wheels were both .44. I don't know how to calculate this offset to compair my 2 sets. I placed a straight edge across the outer face of the presumed 65-66 wheels. The measured distance from the face of the wheel to the face of the center hole is ~2-11/16.

I don't want to buy radials or mount whatever I buy on these wheels unless I am fairly certain there will be no problems. I don't want to find that they rub against anything.

Questions:

• Is the offset of this second of wheels the same as the oriignal '64 wheels and if so can I safely use these wheels without interference problems?
• Most tires I have checked data on in 205/70 and 215/75 sizes have "section widths" of approximately the same dimension as the 7.75 tire so if it was rubbing why wouldn't these sizes of radials also rub?
• What size radial will produce correct speedometer readings?

Thanks for any input.

[Michael H.]

Re: Oh no! More C2 tire questions

Most tires I have checked data on in 205/70 and 215/75 sizes have "section widths" of approximately the same dimension as the 7.75 tire so if it was rubbing why wouldn't these sizes of radials also rub?

• What size radial will produce correct speedometer readings?

Thanks for any input.

Doug,

I have 205/75's on correct 65-66 wheels on my 66 and they're perfect. Zero clearance issues and the size is very close to the original so the speedo is accurate.

[Duke W.]

Re: Oh no! More C2 tire questions

205/75R-15 and 215/70R-15 are the closest in revs/mile to the OE 6.70-15 and 7.75-15, so speedo/odo accuracy is minimally affected. The former are all hard compound S-rated without a nylon cap belt and provide only minimal grip.

If you're lucky, you still might be able to find a set of 215/70ZR-15 Pirelli P4000 Super Touring tires, which is the the best all around tire you can run on a C2, other than the Avon CR6ZZ DOT legal racing tire in the same size.

All '63-'66 steel wheels are +0.44" offset.

215/70R=15 will work on '67 Rally wheels (+0.060" offset) on most C2s without signficant interference on the fenders, but they might rub on the frame at full steering lock. Lots of information in the archives on this issue. Any interference with the fender lips can be cured by adjusting camber in the negative direction - up to minus 1 deg. front and rear.

To measure offset place the wheel (with or without a tire mounted), outside face down, on a flat surface and place a straight edge across the top. Measure from the straight edge to the surface and call this dimension A. Measure from the straight edge to the wheel mounting plane and call this B.

Offset = B - 0.5(A)

Duke

[David L.]

Re: Oh no! More C2 tire questions

but I think the "JK" indicates OE wheels).

I read in this forum that the offset of the correct 64 wheel and the OE 65-66 wheels were both .44. I don't know how to calculate this offset to compair my 2 sets. I placed a straight edge across the outer face of the presumed 65-66 wheels. The measured distance from the face of the wheel to the face of the center hole is ~2-11/16.

Doug,

Original 65-66 Corvette steel wheels have the "JK" stamping as well as the 65-66 Corvette service wheels.

To calculate the offset measure the total width of the wheel. Divide this measurement by 2 and then subtract the backspacing. Backspacing is the measurement from the back edge of the wheel to the mounting surface.

The maximum width of a 1963-1964 wheel measures about 6 9/16" (6.56"). Half of this is 3 9/32" (3.28").
The backspacing measures about 3 23/32" (3.72").
Offset = 3.72" - 3.28" = 0.44" or 7/16"


Dave

[Michael J.]

Re: Oh no! More C2 tire questions

If you're lucky, you still might be able to find a set of 215/70ZR-15 Pirelli P4000 Super Touring tires, which is the the best all around tire you can run on a C2,
Duke

I would agree with Duke about the P4000s, I bought a set about 6 months ago, and Discount Tire only had 20 remaining nationally at that point, so better hurry and look around.