Team ZR-1's Suspension Project

Tip from: Ted Zaleski :

I don't have any reference to look up the gear ratios.  But, assuming the transmission is in the car and you can drive it, a quick way to determine the approximate gear ratios is to drive it at 2000 rpm (suggested) and record the speed from the speedometer.  Fourth gear is direct drive (1:1)
To determine the other ratios, divide the speed in fourth by the speed at the same rpm in the other gear.  For example, if you're doing 50 mph @ 2000 RPM in 4th gear and 37mph at 2000 rpm in 3rd gear, divide 50 by 37 to get
the approximate 3rd gear ratio (1.35 in this case).  Normally, 1st will be around 2.5 or more, 2nd will be around 1.9, and 3rd around 1.3.

If this isn't accurate enough, you can also raise the rear wheels and
physically turn the engine one revolution by hand at the harmonic balancer in each gear and observe driveshaft rotation.