S
sbosbach141157
Guest
I recently swapped the 37/11 rear drive on my 83 R80RT for a 32/11. I found the drive on ebay, parted out from a 79 R90. The drive turned out to be in fairly good condition and by the ware on the splines it looks like around 30K on it. Since the R90 of that vintage used a wider wheel and brake shoes, I had to make an 8mm spacer for the rear axle so the wheel wouldn't jam against the drive housing.
A side effect, the speedo is now accurate, using a Bridgestone BT-45 110/80-18 on the rear. I went with the lower profile tire so I could back the bike into the garage with my short legs! With this size tire, and the original gearing, I was spinning much too high in each gear. From published gearing charts, I estimated a drop of 500 RPM in each gear would get me down to a more normal RPM.
I'm a small guy, so I estimated I could get away with the jump to a 32/11, and I was correct. I can easily start in 1st in any situation and cruise at 60 MPH at 3700 RPM. Sustained speeds of 70 (4400 RPM) are now possible without buzzing my brains out.
A side effect, the speedo is now accurate, using a Bridgestone BT-45 110/80-18 on the rear. I went with the lower profile tire so I could back the bike into the garage with my short legs! With this size tire, and the original gearing, I was spinning much too high in each gear. From published gearing charts, I estimated a drop of 500 RPM in each gear would get me down to a more normal RPM.
I'm a small guy, so I estimated I could get away with the jump to a 32/11, and I was correct. I can easily start in 1st in any situation and cruise at 60 MPH at 3700 RPM. Sustained speeds of 70 (4400 RPM) are now possible without buzzing my brains out.