A guy at work has decided to take his 84 T/A off the street and run it full time. He is now going to ditch the heavy *** street tires and rims he has. How much rim and tire can he safely fit under the rear of this thing. He's currently running a 3.73 w/ a 26" tall et street. He is considering a 4.10 so he could go taller with the rear tire but he doesn't want to spend money on something that might grow to tall and rub. He is currently running a corvette rallye at 15x8 w/ 4" bs. How much backspace is he limited to. Thanks for your help.

 

Tire height and gear ratio depend on the rpm range of the engine. You want to be at or slightly above the shift point in high gear as you cross the finish line.

3.73 and 26" tall tires may limit the rpm to 5500 or so. If the engine revs much higher than a deeper gear is needed so that you'll use the entire rpm range in all the gears for the full 1/4 mile. Putting a taller tire on means going to even more of a deeper gear because it has less revolutions in the 1/4 mile than a shorter tire.

Build the engine however you want for whatever rpm range and HP level you want. Stuff the tallest tire you can under the fenders since it gives a bigger footprint from front to back which is better for traction. Then, based on the engine's shift point and the tire height, you can calculate what gear ratio works best.

Even if everything calculates out properly, if you use an automatic transmission, the converter's stall speed will be another factor in the final rpm.

I started off with 3.27 gears and 26" tall tires. Shifted at 6800 and crossed the finish around 5000 rpm. Very bad gear ratio. I bumped up the gears to 4.10 and increased the tire height to 28" (27.3" actually) and crossed the finish much closer to the shift point but still a little low. Last year I had 29.5" tall tires and 4.56 gears. Shifted at 7000 and crossed the finish at 7200. This year I have 32" tall tires and everything else is the same. I should cross the finish line closer to 6800 rpm with the 4.56 gears.

My converter also stalls at 6000 rpm. I launch at 4500 and the rpms quickly climb to 6000 right after I launch. About 2 seconds out of the hole I'm at 6800 where I shift my powerglide from low to high. The rpms drop back to 6000 after the shift and climb to 7200 as I cross the finish line.

As for rim size, the most common large rim on the rear with little to no modifications is 15 x 10" with 5.5" backspace. A 28" tall tire has no clearance problems. Taller than that and some inner fender modifications are needed.

 

Quote.... As for rim size, the most common large rim on the rear with little to no modifications is 15 x 10" with 5.5" backspace. A 28" tall tire has no clearance problems. Taller than that and some inner fender modifications are needed.

Thanks Stephen...thats exactly the info I was looking for. Much appreciated.

 

Fronts: 15 x 3.5 Moroso DS2 tire, 26 x 4.5
Rears: 15 x 10 5.5 BS Hoosier 28 x 9 slick

No modifications to the sheet metal.

 

front: 15x4, M/T sportsman pros 28x7.50
rear 15x8 with 4.5bs, 28x10.50 ET drag

on my camaro in sig.

 

Thanks for the pics guys....don't mind spending the money, just don't want to have to do it twice. Thanks again.

 

15x3.5 front 165 15 tires
15x8.5 rear with 4.5 BS 28x9 M/T