Chain and Sprocket Calculators

Calculators for chain length and sprocket sizes limited to the chain size for the 650GS.

The chain calculators below do not have allowances in the calculations for the chain slack required by the geometry of the rear suspension. They rely on the allowance for slack BMW allowed in the standard chain and sprocket set.

Basic Sprocket Dimensions

The chain is 112 links of 520 (5/8" x 1/4")
There are minor differences in roller and pin diameters
between manufacturers and chain types so be warned.
The diameter of a sprocket is the line through the centre of the chain rollers.
It is a simple calculation to find the 650GS sprocket diameter.

Enter No of Teeth    Chain Pitch = inches

   Diameter = inches     mm

Distance Between Sprockets

When calculating the number of links needed in a chain, the centre to centre distance between the sprockets is needed. For the standard sprocket set BMW calculated the number of links needed and allowed for chain slack to suit the suspension geometry. This length can be used to make calculations for non standard sprocket sizes

Enter the front and rear sprocket sizes and the number of links to calculate the sprocket centre to centre distance.


Front Sprocket

Rear Sprocket

Number of Links
Distance C to C

Number of Chain Links Needed

The distance between sprockets for the standard GS chain is 24.966 inches. This figure can be used to calculate the number of links needed in a chain when using different sprocket sizes. Add 0.75" when fitting an 18" rear wheel.

Enter the front and rear sprocket sizes and sprocket centre to centre distance to calculate the number of links.

If your result is an odd number of links add one link to get an even number


Front Sprocket

Rear Sprocket
Distance C to C

No of Links

Chain Length in inches and Millimeters

The calculation of chain length is easy and measurement is worthwhile in determining chain wear. Regina Chains
are more forthcoming than other manufacturers on wear and technical data. Some of the mild steel rear sprockets supplied with kits will wear out well before the chain and front sprockets. There are circumstances where replacement of the rear sprocket only is appropriate. The initial length of a chain can be calculated below.

Enter No of Chain Links

The Terra chain length is stated as 114 links but it is unknown if this is for the 17" ABS model or the 18" non ABS model. If it is the 18" then the ABS model would have 112 links as per the 650GS.