Tire Sizes

[Patrick H.]

All,

I am wondering if others could give me some information on the tires they use on a regular basis for their 69-72 Corvette. The Judging Manual states that 215/70R15 is the closest size match to the originals, but I know that 225/70R15 matches the 73-82's, and is slightly larger. Does anyone know if they actually changed speedo gears to accomodate the different size tires, or did GM call it "close enough", and leave them the same. I am mostly wondering if the difference in circumference is significant enough to cause a lot of speedo error.

Also, I know many people who use the 235/60R15 tire as well. Does anyone have experience with good high performance tires in this size?

I am trying to get the "highest performance" tire possible for my 71 (within reason), and I think that I can likely do better than a BFGoodrich Radial TA or Firestone Firehawk SS-10.

Any thoughts?

Patrick

[Jack H.]

Re: Tire Sizes

Running BFG 215-70-R15 on 'Lil Red ('71 roadster). No complaints.

[Jack H.]

Re: Tire Sizes

Running BFG 215-70-R15 on 'Lil Red ('71 roadster). No complaints.

[Rick Garrett]

Re: Tire Sizes

I am running BFG 235/60's on my 71 and they are great. I tried 225/70's but they will rub the front fenders, so I swapped for the 235/60's. There is noticeable better traction in the 235 from the 215's.

[Rick Garrett]

Re: Tire Sizes

I am running BFG 235/60's on my 71 and they are great. I tried 225/70's but they will rub the front fenders, so I swapped for the 235/60's. There is noticeable better traction in the 235 from the 215's.

[Joe L.]

Re: Tire Sizes

Patrick----

Your '71 was, of course, originally equipped with F70-15 tire size. These tires have the following specs:

diameter=26.97"---section width=8.95"---tread width=6.5"

SIZE 215-70-R15 specs:

diameter=26.8"---section width=8.7"---tread width=6.6"

SIZE 225-70-R15 specs:

diameter=27.4"---section width=8.9"---tread width=6.7"

SIZE 235-70-R15 specs:

diameter=27.9"---section width=9.4"---tread width=7.4"

SIZE 245-60-R15(what I've used for the street for the past 15 years)specs:

diameter=26.5"---section width=9.7"---tread width=8.3"

I don't have any information on 235-60-15.

All of the above tire sizes(except 235-70-R15) will produce negligible speedometer error, not correctable with a speedo driven gear change. Don't forget, GM did not produce an infinite number of speedo drive and driven gear combinations. For a given transmission/rear axle ratio, the same drive and driven gear combination would be appropriate for either F70-15, 215-70-R15, 225-70R15 or 245-60-R15. The only means of further correcting speedometer error produced by available gears is with a speedometer adapter. This is an expensive and, usually, unnecessary refinement.

[Joe L.]

Re: Tire Sizes

Patrick----

Your '71 was, of course, originally equipped with F70-15 tire size. These tires have the following specs:

diameter=26.97"---section width=8.95"---tread width=6.5"

SIZE 215-70-R15 specs:

diameter=26.8"---section width=8.7"---tread width=6.6"

SIZE 225-70-R15 specs:

diameter=27.4"---section width=8.9"---tread width=6.7"

SIZE 235-70-R15 specs:

diameter=27.9"---section width=9.4"---tread width=7.4"

SIZE 245-60-R15(what I've used for the street for the past 15 years)specs:

diameter=26.5"---section width=9.7"---tread width=8.3"

I don't have any information on 235-60-15.

All of the above tire sizes(except 235-70-R15) will produce negligible speedometer error, not correctable with a speedo driven gear change. Don't forget, GM did not produce an infinite number of speedo drive and driven gear combinations. For a given transmission/rear axle ratio, the same drive and driven gear combination would be appropriate for either F70-15, 215-70-R15, 225-70R15 or 245-60-R15. The only means of further correcting speedometer error produced by available gears is with a speedometer adapter. This is an expensive and, usually, unnecessary refinement.