Determining Suspension Travel in the Damper
To determine how much suspension travel your vehicle has, do the following:
ride height measurement.
2) Jack up your car until your wheels are off the ground. Measure again. We'll call this your droop height measurement. The two measurements should look somewhat like this:
3) Remove a shock and/or strut. We will need to see how much travel it has. If you can compress the shock by hand and measure its compression, that's great. If not (the gas pressure in dampers can be quite high), just measure the shaft of the damper, as shown. This is our damper travel measurement.
4) If you have a bump stop (sometimes called a jounce bumper) on the damper, measure to where that is, too. This is your linear damper travel. We'll elaborate on this later.
5) Determine your motion ratio. (See: Motion Ratios)
6) Reassemble. Now, you have four measurements- your ride height, droop height, damper travel, and motion ratio. From these measurements, you can quite easily calculate how much suspension travel you have. First, we need to figure out how wheel movement translates into damper movement. This is what the motion ratio tells us. The equation for this is:
wheel travel * motion ratio = damper travel
Or, going the other direction, we can figure out how much wheel travel the car has based on available damper travel:
damper travel / motion ratio = wheel travel
In the first damper pictured above, we see about 6.5 inches of suspension travel. The motion ratio for this car is 0.97, so the wheel travel permitted by the damper is 6.5 / 0.97 = 6.7 inches.
In the picture above illustrating wheel travel, a difference between ride height and full droop of 3 inches was recorded. Since we know there is 6.7 inches of total travel, and 3 inches of that is droop travel, we know that there is 3.7 inches travel remaining as bump travel. 3.7 inches of travel in the bump direction is quite a bit for a road car!
However, there are other things that can limit suspension travel. Among them are tire clearance, spring travel, and bump stops (jounce bumpers). Continue reading for more on those!