How to adjust suspension preload
You may have heard the term preload and how to adjust preload before. In this article we will be discussing what preload is, how to adjust it, and the benefits of doing so in regards to aftermarket coilovers.
What is preload?
Preloading involves compressing the springs to reduce the level of play in the springs. The more you compress the spring, the less distance the suspension has to travel. Therefore, when the compression of the spring is increased, the amount of travel the suspension has to travel when the suspension takes on the weight of the car will be reduced.
Preload is independent of spring free length. For example, a 15" long, 100lb/in spring with 1" of preload will give you the same ride height as a 10" long, 100lb/in spring with 1″ of preload.
In both cases you’ve applied 100lb of force before the vehicle weight collapses the spring. Because spring rates are the same, each spring will collapse the same amount under the weight of the vehicle. The result is the same amount of ride height.
The only time spring length can affect suspension preload is if there aren’t enough threads on the shock to get the desired preload, or if the springs will go to coil bind.
Why is preload important?
Preloading your coilovers also reduces the likelihood of the coilover from completely unseating. It's important to prevent the spring from unloading to the point where the spring becomes off-centered and is unable to properly re-seat itself. Secondly, each spring is designed to operate under a certain preload. By preloading your coilovers to the manufacturer’s recommended load, the coilovers will be able to operate at its intended specs.
Everyone thinks about what happens when springs compress, but it’s also important to consider what happens when the springs extend. Spring preload pushes the wheel/tire downward and makes the suspension work. On big bumps, the suspension preload pushes the tires down to better follow the terrain and make a smoother, more controlled ride. Under articulation the spring preload increases tire contract pressure improving traction.
How to adjust coilover preload
- Loosen both lock rings under the spring (spring seat ring(top) and spring lock ring(bottom)) so that the spring is loose and can move up and down slightly.
- Tighten up the spring seat ring so that the spring is snug, but do not tighten it down past simply holding the spring snug, this will be zero preload.
- Now bring the bottom lock ring up so that it is just touching the spring seat ring, but do not tighten to lock, you will be moving the spring seat ring next.
- Now tighten up the spring seat ring so that you are now preloading (compressing) the spring.
- Measure the distance between the bottom ring and the top ring as you are tightening, once there is a 3-5mm gap between the two rings, you have 3-5mm of preload on the spring. The thickness of the lock ring wrench is 4mm, so when you can slip the wrench in between the lock rings, you're good to go.
- Tighten up the lock ring to lock your preload in place.
- Repeat for all four corners.
Check and make sure the top center nut is tight. It is recommended to check this nut with an impact gun. A quick hit with an impact gun is all it should need to stay tight and snug. If you do not have access to an impact gun, you can use an allen key to hold the shaft in place and tighten the nut with an open socket or wrench. You don't want the shaft to spin while you are tightening it, otherwise it will not tighten or tighten enough. A few other areas to check are the lower mounting bolts, the allen bolts that adjust camber if fitted with camber plates, and the four lock bolts underneath the pillowball bearing if fitted with pillowball mounts. Make sure all fasteners are tight as they can cause problems later down the road if not properly tightened.