In this article we will go over ride height and how it is one of the most critical settings on a suspension with respect to shock travel. Ride height also affects suspension geometry as well, which we will discuss in a future article. First, let's discuss a few basic topics related to ride height: bump, rebound, stroke travel and spring pre-load.
IMPORTANT TERMS TO UNDERSTAND
Bump: The compression of the suspension in relation to the chassis. Bump occurs when the suspension is compressed either from chassis roll, which occurs on the "outside" suspension, or a physical bump on the road surface pushing the suspension up.
Rebound: The extension of the suspension in relation to the chassis. Rebound occurs when the suspension is extended either from chassis roll, which occurs on the "inside" suspension, or the wheel returning to the ground after being compressed from hitting a bump in the road surface.
Stroke: The amount of distance the damper can move through rebound and bump. Total stroke distance is measured from full rebound to full bump. This is an important measurement because at ride height, we need to have sufficient travel for both bump and rebound.
RIDE HEIGHT VERSUS DAMPER STROKE POSITION
Let's say we have a scenario where the damper has a total stroke of 5 inches...
Ideally we want the damper to be compressed roughly half way at ride height allowing for approximately 2.5" of bump travel and 2.5" of rebound travel. How much it compresses will be determined by the weight of the vehicle and the spring rate. Other factors such as motion ration, bushing spring rate also play a factor. With a road and/or track car the spring rates are typically soft enough to allow sufficient compression. However, on a racecar you will have a high spring rate and a light car which may not compress the damper sufficiently. There are ways to design the spring package around this which we will cover in a future article.
However, what if we have an ideal ride height but the damper compresses 4 inches where you only have 1" of bump travel and 4" of rebound? This is VERY common with typical dampers and is not good as you will bottom out frequently which will cause handling problems and potentially damage your suspension. (See bump stop section below for more details) The only solution is to raise the spring perch or add spring spacers but unfortunately our ride height will then be too high.
IDEAL RIDE HEIGHT ADJUSTMENT METHOD
It is possible to adjust ride height without using the spring perch. Instead of changing the ride height with the spring perch, with Ohlins you can change the location of the mounting point of the suspension on the damper itself. Damper stroke position problem solved! With this method, you can now precisely set the stroke position using a combination of spring height and spring perch location. Then precisely set ride height with the location of where the suspension mounts to the damper. Win Win. Now we can get into more advanced suspension setup such as corner weight adjustment, bump stops, etc.