How to Measure for Shock Absorbersby Robert Bayly
The need for measuring shock absorbers arises when you change the ride height of your vehicle. This is especially true for a 4x4 that has been lifted, but is also important for a vehicle that has been lowered. The shock on a vehicle needs to match the suspension travel. If the shock is fully compressed before the suspension bottoms out, you will damage the shock. Likewise, a shock that is fully extended before the suspension reaches its full travel may be subject to damage because the suspension might pull on the shock as it tries to extend. A few quick measurements can tell you what length of shock you need.
Park the vehicle on a level surface. Measure the distance from the lower shock mount to the upper mount for the front and rear shocks. Write this down. This is the "static" measurement.
Locate the rubber bumpstop on the front suspension. Measure the distance from the bumpstop to the spot on the suspension where it makes contact. For instance, the front bumpstop usually hits the lower control arm, while the rear bumpstop usually hits the rear axle tube. Write this down.
Subtract the bumpstop measurement from the static measurement. This is the compressed measurement of the shock. For instance, if your front shock's static measurement is 14-inches and the bumpstop measurement is 4-inches, the compressed measurement is "14-4=10," or 10-inches.
Raise the front of the vehicle until the tire is off the ground. Measure the distance from upper to lower shock mount. Write this down then lower the vehicle. This is the extended measurement for the front shock.
Raise the rear of the vehicle until the tire is off the ground. Measure the distance from upper to lower shock mount. Write this down then lower the vehicle. This is the extended measurement for the rear shock.
Refer to a shock absorber catalog. You should be able to find one in an auto parts or aftermarket parts store. You will need the compressed and extended measurements for the front and rear shocks.
- You may find it difficult to get an exact match. This is because the compressed distance is usually less than the extended distance. Therefore, you should concentrate on the compressed distance because it is much more likely that you will at some time bottom out your suspension. Reaching fully extended distance would require getting the tires off the ground, which is not likely in everyday driving. For a 4x4 vehicle driven off road this may happen. If you have a 4x4, you may want to consider installing "limiting straps" which limit the extension travel of the suspension. This will protect the shocks and the suspension in general.
Items you will need
- Shock absorber image by Neryman from Fotolia.com