After swapping in a new drivetrain in my project 1969 Barracuda, I needed to get the right speedometer pinion gear in the transmission. With a 2.76 gear and 25.5 inch diameter tires, the charts call for a 29 or 30 tooth gear. I installed a 30 tooth gear I had and went for a drive. The speedometer is reading 26% high! I can get a different gear to correct the speed, but I can't believe the charts did not get me closer. Is there some other issue that would explain the error? The speedo needle is steady and quiet.