My brother is trying to figure out what gears to put into his tranny to make the speedo right. Currently its reading about 75 mph at 60 mph.

He is running a 26" tall tire and 3.73 gears. I know I have found a chart for automatics, but don't know if I have found one for manuals.

Any help would be appreciated

 

What year T5 is it?

 

If this is from a 3rdgen ('82-'92) camaro/firebird, check over on thirdgen.org in the drivetrain forum. They have a complete chart of speedo gear combos for various gears.