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Specialized in vintage Harley Davidsons.
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Belt lengths, Pulley sizes, Drive ratios

Unlike a chain, a belt cannot be easily extended or shortened to accomodate different pulley sizes. Therefore, it is important to make a good choice in pulley sizes and belt length to obtain a desired drive ratio while maintaining a proper center to center distance between the pulleys. Below is a calculator applet where you can calculate enter front and rear pulley or sprocket sizes and belt or chain length, and which calculates the final drive ratio and (an approximation of the) center to center distance for the pulleys or sprockets. Below that, there some numbers are given for factory equipped shovelheads.

Use the applet and information below to make an educated decision when you want to convert from chain to belt or when changing pulley or sprocket sizes, belt or chain lengths. You can for instance compare the calculations to your current situation to determine whether the slots in your swingarm provide enough clearance for a desired new configuration.

Drive ratio and Center to Center distance

Input >>>> Output
Belt Chain
Number of Transmission Sprocket Teeth
Number of Rear Sprocket Teeth
Number of teeth/links of belt/chain
C-to-C distance
Drive Ratio

Here are some numbers on HD's as they left the factory:

Models Transmission teeth Rear teeth Belt/chain length C-to-C Ratio
All final belt drive Shovels 33 70 126 20.27" 2.12
FX Chain drive Shovels 23 51 102 20.12" 2.21
FL Chain drive Shovels 22 51 102 20.26" 2.31

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