This week, we had a client of ours ask us about which rear axle ratio he had installed in his Bugeye. On a normal classic, determining this would involve jacking the rear wheels off of the ground and counting rotations on your driveshaft per 1 wheel rotation; however, on Bugeyes and Spridgets, it’s as easy as looking at the side of the differential carrier!
On each differential carrier, near the top above the hole where the rear brake union mounts, there is a flat boss; on that boss, there is a stamped number. This is the number of teeth on the pinion (the lower number) and the number of teeth on the ring gear (the larger number). In order to determine what ratio you have, just divide the larger number by the smaller number, and you have your ratio!
Bugeyes and Mark II Sprites/Mark I Midgets came from the factory with 4.22 axle ratios. Over the years, a lot of people have swapped in optional ratios from later years in an effort to keep RPMs down at higher speeds; 3.9 seems to be the popular swap as they were available for longer, but later 1500 Midgets could have 3.73 or even 3.55 ratios installed. The video below (shot all the way back in 2011!) explains how to tell what ratio is in your car, as well as some examples of RPM ranges for the different ratios.
If you find yourself swapping your differential, we offer other parts you will need to finish the job right! Click on the photos below for some examples or click here for our full catalog!