Friday, February 20, 2015

How To Determine Chopper Final Belt Drive Length

How do you determine the length of the final drive belt that you need for your custom bike? Here at Rullo Custom Cycles, we have been answering this question for many years and this How-To article will describe in detail the best method for measuring final drive belt length.

If you are changing your pulley size, hard-tailing your frame, switching to a rigid frame from a stock swingarm frame, making a swingarm length change, or otherwise changing the distance of your transmission main shaft to your rear axle, you will need to determine the length of belt for your customized bike.

There are generally 3 brands of belts that are popular for Harley and custom motorcycles: Gates, Dayco, and Goodyear. Gates are sold by this name, and they make OEM Harley belts. Dayco is sold under the Panther brand. Goodyear is sold under the BDL Falcon brand, and Drag Specialties brand. The sizes of the belts that each company make will vary, although many of the common sizes are made by all three manufacturers.

To measure for final drive belt length you will need to determine three variables on your motorcycle:
  1. Transmission Pulley (front pulley that drive belt uses) tooth count
  2. Final Drive Pulley (rear pulley mounted to rear wheel) tooth count
  3. Distance Center to Center of the Transmission Pulley to Final Drive Pulley
The tooth count for your pulley should be determined by the number of "low spots" on your pulley where the drive belt teeth will ride. Some pulleys will list on the back face the tooth count, but many will not. Count them, if necessary, by marking the first tooth and physically counting the rest. The distance from center to center of the trans pulley and final drive pulley can be thought of as the center of the trans main shaft to the center of the rear axle. Check out the diagram below:

After you have determined the teeth on your Transmission Pulley and Final Drive Pulley and measured Center to Center distance see the chart below.

* "Center to Center is measured from the Transmission Pulley Center to the Rear Pulley Center
* "Pulley Teeth" is listed front pulley-rear pulley
* Measurement data is in inches (in)
* Belt length is by teeth
* This chart has information was gathered courtesy of Belt Drives Limited (BDL)

Generally, one tooth change on the transmission pulley will mover the rear axle approximately .125". One tooth change of belt length will move the rear axle approximately .280".

Check out our Gates, Panther, and BDL final drive belts on

1 comment:

  1. Best, easiest to understand explanation I've found. I was searching for something I could print out for the guys at my shop. The other literature I came across before I found yours was beginning to confuse me! I've been wrenching on Harleys for40 years!