Motorcycle Anti-Squat Calculator


Screen capture of the Excel anti-squat calculator.

The anti-squat calculator shows results for two geometry setups, displaying a graph of anti-squat percentage or angle vs. wheel travel, and a line diagram of the motorcycle’s layout with the relevant force lines for each setup. The calculator also outputs a polynomial equation for anti-squat that can be used as a math channel in a data acquisition software package.

More information about anti-squat: Anti-Squat Geometry

Download the Excel file here: Motorcycle Anti-Squat Calculator

In the Excel anti-squat calculator, input values for rear tire diameter, wheelbase, swingarm pivot height, swingarm length, and the x/y co-ordinates of the countershaft sprocket relative to the swingarm pivot. The program assumes that the center of gravity is midway between the axles and at a height of one-half the wheelbase. In addition, front and rear suspension are assumed to move an equal amount.

The top chart shows a line diagram of each setup, along with the relevant force lines. The slider on the chart will “move” the bike through its suspension travel, and the change in geometry can be visualized.

The bottom chart shows a graph of anti-squat percentage or angle vs. suspension travel; a drop-down menu on the chart can be used to select which variable to display. The vertical dashed line on the chart indicates the suspension position in the line diagram. The equation for percentage or angle (depending on which is selected) is also shown.

Some adjustments to make in the anti-squat calculator that will show how certain geometry changes affect anti-squat:

  • Experiment with gearing changes, with both shorter and taller gearing. Also use settings that give the same overall gearing ratio but different sprocket sizes, such as 15/45 for one setup and 16/48 for the other.
  • Raise and lower the rear ride height by changing the swingarm pivot height value.
  • Lengthen or shorten the swingarm.
  • Raise the swingarm pivot by increasing swingarm pivot height and decreasing y an identical amount.
  • Extend the wheelbase.
  • Try to find a setup that gives a theoretically ideal 100 percent anti-squat over the full travel of the suspension (hint: x will have to be negative, with the swingarm pivot in front of the countershaft)

Version history:

  1. June 14, 2016 – original
  2. June 24, 2016 – added functionality for maximum travel input