How to determine your belt lenght
When changing your Harley Davidson final belt drive you probably have little difficulties finding a replacement belt. Most reproduction belts can be identified by the Harley Davidson replacement numbers.
The problem starts when you have changed the setup of your bike or you are building a new one from scratch and there is no way you can relate to the stock belts that are used.
To get you started there are some little tools that can help you determine the correct belt length for your bike. Also don’t forget to measure the width of your belt. Harley Davidson uses 1 ½”, 1 1/8”, 1” 20mm and 24 mm wide belts. The correct determines on your model/production year and/or if you modified the pulleys.
When using a stock bike but you only changed the front/rear pulley you can use this conversion table to determine the correct belt length.
Number of tooth required on belt with specific drive ratio on stock frames with stock swingarms. Note: 00-07 Softail models add 3 tooth to the belt.
61 Tooth Rear
65 Tooth Rear
70 Tooth Rear
Note: If you also changed the length of your swing arm this table is useless and you will have to start calculating. Luckily the formula to do this isn’t that hard.
3 step formula:
A= number of tooth rear wheel pulley
B= number of tooth transmission pulley
C= center to center distance between both pulleys in mm
( C * 2 ) / 13.8
( A + B ) / 2
Step 1 + Step 2 = number of tooth required on belt.
A = 70 tooth
B = 34 tooth
C = 584mm
( 584*2 = 1168 ) / 13.8 = 84.6
(34 + 70) / 2 = 52
84.6 + 52 = 136.6 teeth => The recommended belt would be 137 tooth.
Information used from the MCS website.