How To Install Coilovers
What is a Coilover? A type of adjustable suspension where the ride height can be altered by changing the spring preload. Generally speaking the coil spring is mounted on the damper and the spring is usually parallel. Occasionally some of the cheaper coilovers have a generic cartridge that fits into a model specific bracket or plug. These can be changed in length as well as changing preload.
Most cars on the market today use MacPherson strut suspension on the front and some type of beam axle on the rear. Many of the rear coilover set ups do not have the spring and damper together so aren't strictly coilovers. However they do usually have an adjustable spring platform that allows adjustment of Preload and hence ride height.
Installation of fixed spring seat suspension is simple. You just install the springs using spring compressors (or by lowering the axle beam), refit and get the tracking adjusted. That's it.
With the Coilover Suspension System there are plenty of opportunities to really muck up the install. The first and most common mistake is to not measure the ride height before starting.
Disclaimer - this guide does not cover basic mechanical safety e.g use axle stands, wear gloves, use the correct tools if you have an accident it's your fault not ours ! etc
Step 1 - Measure the ride height from centre of the wheel to the bottom of the arch. Do this on each corner and ensure the ground is level. The readings may well not be the same from left to right on each axle - this is normal. Also take a measurement from sill to ground to see the rake built into the chassis (10-25mm is normal)
Step 2 - If you have coilovers that allow the units to be changed in length you need to decide how short you want the units. This is often a case of trial and error as for example if they are too short you may need too much preload to keep the car from being "slammed" which might then result in so little droop that the tyres leave the tarmac regularly. Naturally the amount of droop for a race car will be very different to a road car. As a guide I would suggest something like 2-3 inches shorter. If you have more conventional coilovers then you won't have this problem.
Step 3 - Install the suspension as per the instructions (many kits don't have any - they just assume the expertise of the fitter). The most important tip is to ensure that the spring seat on the front units is measured to a reference point (e.g the bottom of the unit) and that front left and front right match each other. The same should be done with the rear. It is very important to ensure the spring has enough preload so it isn't loose and doesn't easily turn by hand. At this stage if the instructions tell you where to set the spring seat (Tein do for instance) then set correctly. If not lightly seat the springs with enough preload to ensure the spring is not loose. This will be the LOWEST setting you can achieve.
Step 4 - Once installed and dropped off the jacks the car may well sit high. Drive the car a few yards (ideally not on the public road) to ensure any stiction is removed and the suspension settles. Now recheck the ride height. Again the measurements won't necessarily match left to right BUT you should see an equal reduction from your original figures from left to right. Ensure that the rake is maintained - e.g if the front has gone down 20mm but the rear 30mm then 10mm of rake has been lost. The front should sit lower than the rear to help reduce lift at speeds. If the ride height is too low, you might now want to add preload to each corner ( again measuring to ensure the spring seats are in the same position left to right on each axle) to raise the car. If the units are adjustable for fitted length you can change that rather than preload to raise the car. The most important thing when choosing any ride height is to ensure the springs are not loose and easy to move when the suspension is in droop. It is an MOT failure and dangerous. Doesn't work well on a road car or a race car. If you need it lower you can either reduce preload or shorten the unit. A helper spring may assist you, but make sure you don't end up sat on the bumpstops with no more compression travel and only rebound. There is a reason the saying "Slow and Low" exists.
Step 5 - Look at the position of the front wishbone - on a MacPherson strut if you lower too far the wishbone will start to point upwards at the outboard end - this is NOT GOOD for handling.
Step 6 - Look at the driveshaft position - excessive lowering puts strain on the driveshafts.
Step 7 - When you are happy with the ride height and the rake, get the alignment adjusted. Usually on most cars the toe setting will change under compression. Mostly toeing out on the front, and toeing in on the rear.
Step 7 - If you are looking to do track work then corner weighting may well be worthwhile. If you've followed the instructions regarding setting the spring seats evenly side to side, then even though your arch gaps may be different from left to right, the cross weight will be close to 50%. Some people make the mistake of trying to get each arch gap the same, and that usually throws the cross weight right out.
Step 8 - Remember optimum looks, and optimum handling don't always equate. Eibach ProKits are very well designed, and the lowering they offer is usually the maximum that the chassis will stand, without negative effects, hence they tend to have TUV Approval. Set your ride height at the level that still ensures you have some suspension travel in compression.
Every chassis is different but as a guide 20-40mm is about right. On a decent race car every aspect of the suspension is looked at to achieve the lowest ride height possible - moving pick up points, checking and modifying bump steer, establishing and adjusting roll centres. Most modified cars have none of this attention to detail and rely on the tolerances within the standard design. Some will spend £15,000 on their 700hp engine only to fit £500 of suspension, lower 70mm and then drive round on 20 inch lead wheels with budget tyres. Not a recipe for rapid progress, even in a straight line.