my oringinal tire size was 205-70-14 with 308 gears with a 84 700r4. I switched to 255-60 -15 in the rear with a 327 rear end installed. To my surprise as I went past a portable speed device at 30 mph I was dead on. Would I be at 60 mph the same.? Is it possible for someone to make a chart with tire sizes mating old rear ends with new rims and gears to avoid little to no speed change. I guess some set ups would not be great.

 

I should of went on tranny and drivetrains.I'm very sorry moderators.