In my opinion there is only one way to install coilover shocks in a drag car. Simply put, they need to be vertical when viewed from the rear of the vehicle. They can be inclined slightly forward at the top, but for all intents and purposes, vertical when viewed from the side and the rear is ideal. I know there will be those out there who will critisise this statement (and I know that there are many race cars out there with inclined shocks), but I will explain.
When auto manufacturers install shocks in factory cars, they are usually inclined towards the centre of the vehicle. This is OK in shock only applications as there is no spring to complicate things. Where the shock is stand alone, there is no other force other than damping. Also stock automobiles are required to go around corners and the inclined shock actually helps.
Now consider the coilover. Straight away, an upper and lower spring platform is required to locate the spring. Unless these platforms are level, a side load of some magnitude will be applied, due to the weight of the vehicle. This gets transferred to the shock shaft and ultimately to the shock piston. The shock piston then proceeds to wear a hole in the loaded side of the internal tube that the piston slides up and down in whilst doing its job.
As an example, I have had a customer tow to Perth from Sydney, and return, without supporting the front of his strut equipped car with around 10 degrees of castor. Upon his return to Sydney, the shock piston was right through the inner tube, and the shock was solid. (I am not suggesting we get rid of castor as it is a fundamental front geometry requirement), but where we can eliminate coilover inclination, we should. (Double wishbone front ends are an exception because of the load path scribed by the lower control arm).
The other problem with inclining coilovers towards the centre of the vehicle is to do with weight loading on the rear tyres. When scaling cars with inclined coilovers, rear weight distribution on the tyres alters dramatically with adjustment of the track locater. If the housing is moved off centre, one coilover will incline more, whilst the other will stand more upright. The weights change on the scales accordingly; if the same thing was done at the track, an otherwise good handling car will start going either left or right depending on which way the housing was moved.
I believe inclined coilovers are dangerous due to the fact that a correctly set up car, can be changed to an ill handling car accidently! If for example the 3rd member is removed at the track, and the track locater removed to give access, rear weight bias can be changed if the track locater is altered in length to reinstall it. This cannot happen with vertically installed coilovers. Both will lean the same amount, one way or the other, if the track locater inadvertantly has its length altered. The rear weights as set at the shop will remain the same.
Rod Andrews
Proprietor
Andrews Race Cars
Installing Coilover Shocks Correctly
Added on 2007-11-28