Calculate the collapsed and extended shock length you need from the mount-to-mount distance and bump-stop gap, or work back from a shock’s length.

Measure at ride height: mount-to-mount distance and the gap between the bump stop and the axle.

Center of the upper mount to center of the lower mount, with the vehicle at ride height.

Gap at ride height; this is the compression travel before the axle reaches the bump stop.

Margins (1 in defaults)
Room left so the shock does not bottom out before the bump stop. This page uses 1 in by default.

Extension beyond ride height. The default is 1 in; enter your measured droop travel for a better extended length.

Shock Length Formula

The following two example problems outline the steps and information needed to calculate the Shock Length.

SHOCK = (D1 - D2) - 1
  • Where SHOCK is the Shock Length (in)
  • D1 is the distance between the upper shock mount and lower shock mount (in) 
  • D2 is the distance between the bump stop and the axle 

How to Calculate Shock Length?

The following example problems outline how to calculate Shock Length.

Example Problem #1:

  1. First, determine the distance between the upper shock mount and lower shock mount (in).
    • The distance between the upper shock mount and lower shock mount (in) is given as 6.
  2. Next, determine the distance between the bump stop and the axle.
    • The distance between the bump stop and the axle is provided as 4.
  3. Finally, calculate the Shock Length using the equation above: 

SHOCK = (D1 - D2) - 1

The values provided above are inserted into the equation below and computed.

SHOCK = (6-4) - 1 = 1 (in)

Example Problem #2: 

For this problem, the variables required are provided below:

distance between the upper shock mount and lower shock mount (in) = 3

distance between the bump stop and the axle = 1

Test your knowledge using the equation and check your answer with the calculator.

SHOCK = (D1 - D2) - 1 = ?