Tire size compatablility for a 77

[stevolwevol]

I am eventually going to replace my tires, maybe next spring. Anyway I have 225/70/15's on the rims now. Will 255/60/15's work, or fit on a 77, and will the speedo read the same with out replacing the driven gear if I made the switch?

 

[Vettehead Mikey]

The difference in OD is not enough to worry about the speedo, but the tread is about 1.1"ish wider. Not sure if that will cause a rubbing problem on the front fender or frame.

 

[stevolwevol]

The difference in OD is not enough to worry about the speedo, but the tread is about 1.1"ish wider. Not sure if that will cause a rubbing problem on the front fender or frame.

Yes, the potential of rubbing crossed my mind. I like the looks of the wider tire. It doesn't sound like much, but it is visible.

 

[SVO]

The original tire that came on your '77 Corvette was a GR70-15, which crosses over to a P225-70R15 in the p-metric sizes on a 8" wide wheel. In 1978, the stock tire for the '78 Corvette was the P225-70R15 and the optional tire was a P255-60R15 on a 8" wide wheel. On the '78's with the optional FE-7 Gymkhana Suspension, GM cut the inner fender well lip off on the front fenders to add clearance with the P255 size tire. The FE-7 suspension lowered the car sightly and I'm guessing tire clearance was a concern to the General. To answer your question, yes, the P255's will fit your '77 on a stock 8" wheel without clearance problems. Even if you have the optional FE7 suspension, I would not expect there to be a clearance problem on the front. A lot of Corvettes out there running the P255's on stock rims with no problems.

On the transmission - speedo question, I do not know. If the P225 has the same or close to same diameter as the P255, your speedo should read the same.

I do know that on my '72, a P245-50R15 on a stock rim will not fit in the rear due to a interference fit with the trailing arm. There are some who call BS on that, saying it should fit with no problems. But it is a '72, not a '77.

 

[stevolwevol]

The original tire that came on your '77 Corvette was a GR70-15, which crosses over to a P225-70R15 in the p-metric sizes on a 8" wide wheel. In 1978, the stock tire for the '78 Corvette was the P225-70R15 and the optional tire was a P255-60R15 on a 8" wide wheel. On the '78's with the optional FE-7 Gymkhana Suspension, GM cut the inner fender well lip off on the front fenders to add clearance with the P255 size tire. The FE-7 suspension lowered the car sightly and I'm guessing tire clearance was a concern to the General. To answer your question, yes, the P255's will fit your '77 on a stock 8" wheel without clearance problems. Even if you have the optional FE7 suspension, I would not expect there to be a clearance problem on the front. A lot of Corvettes out there running the P255's on stock rims with no problems.

On the transmission - speedo question, I do not know. If the P225 has the same or close to same diameter as the P255, your speedo should read the same.

I do know that on my '72, a P245-50R15 on a stock rim will not fit in the rear due to a interference fit with the trailing arm. There are some who call BS on that, saying it should fit with no problems. But it is a '72, not a '77.

I don't know for sure if I had the FE-7 option, and I'm not sure with out looking it up if it was available in 77, but that being said, I doubt it. There is nothing "lower than usual" looking about it, and it's a base L48. The previous owner rebuilt the front end, and put a composite spring on the rear, but nothing else. He even rebuilt the engine a little over 10,000 miles ago, but rebuilt it to stock specs. YUC! Who the heck would do that?? So it stands to reason that the suspension was not modified either. I can't check right now cause it's sleeping in a barn with other antique cars, but in the spring I can have a closer look at the suspension. If nothings in the way I just may go ahead and go with 255's.

 

[revitup]

Yes, the potential of rubbing crossed my mind. I like the looks of the wider tire. It doesn't sound like much, but it is visible.

Here's a pretty good side by side comparison.

 

[stevolwevol]

Here's a pretty good side by side comparison.
View attachment 24088

You appear to be making my point, although they don't look mounted, or inflated. Or they are your bike tires.