Recommended Suspension Systems, written by Claudius

To get a better suspension setup, you will need to have dampers and springs that work well with each other. This is not the case for standard dampers and uprated springs.

What are the advantages of a proper suspension setup?

Better stability
Better control
Improved handling
Less body roll
Increased cornering speeds
Better braking

What about lowering springs, then?

It takes power to stop a progressive rate spring. Your standard springs are not progressive. They are evenly spaced apart. This means when you hit a bump in the road, the entire spring can compress. It takes a lot less power to stop a non progressive spring. Think of it like you have a 1 foot long spring with evenly spaced coils, you hold it down, and let it go. Now you do that again with a 8 inch tall spring that has all the coils near the top all close together, even touching. This means that you have a lot less spring pushing it. But physics says its going to decompress a hell of a lot quicker, thus faster.

Now, I am a supporter of Eibach, they have awesome quality springs. They are a world renoun company. But despite whatever they say, over and over, and whatever your friends or people on this board say, you cant make a shorter, progressive rate spring to work with standard shocks. Its springrate may be at the limits, it may feel about like standard, but it isnt. Under your car your shocks are working the hardest they have in a while to carry that springload.

 

What do I need to look for when choosing a suspension system for my car?

That depends on the use. Let's assume you need the suspension for fast road use. You will need the following:

height adjustabilty (to find the right front / rear balance)
the right springs for the dampers' bump and rebound characteristics

A very stiff spring will not work with a relatively soft damper (this is why lowering springs are not recommended). In fact, the damper may well blow as in break a seal on lose its oil.

On the other hand, a soft spring and a hard damper wont be efficient either: the damper will take all the stress and use up quickly, and the car will roll a lot, given the soft springs.

You really need a well balanced damper / spring setup.

 

What kind of springs do I need?

Springs should first of all be the right length and diameter for the damper. (This is another reason why lowering springs do not work).

Other than length and diameter, spring rate is the main spring characteristic to look for. Anything below 30 N/mm or above 80 N/mm is wrong: below 30 N/mm, the car will roll like a boat, and above 80 N/mm, it will be so hard it will jump all over the place. A good road setup would feature 50 or 60 N/mm springs. This will give very good control and precise handling, but not send all the road irregularities into your spine.

Springs are often referred to in kg as well. When people mention 5 or 6 kg, that is 50 or 60 N/mm. (50 kg/mm would be impossible to move and equate to replacing dampers with a metal bar).

 

How do I adjust the damper to the spring?

Let's say you have chosen 50 N/mm springs for your car (maybe 40 N/mm in the rear if your car hasnt got a 50/50 weight distribution).

Now the damper needs to be adjusted in bump and rebound to suit this spring. Typically, a standard Bilstein or equivalent damper will be too soft to help te spring do its work. A good way of changing the damping characteristics is to change the oil inside the damper to a thicker one and to uprate some of the rubber parts inside. Very few companies can do that right, so a good idea would be to get adjustable dampers.

 

What are Adjustable Dampers?

Adjustable dampers are dampers the setup of which can be changed. Sometimes, height adjustable dampers are referred to as adjustable, when in fact only the ride height can be adjusted.

Truly adjustable dampers can be adjusted in height, bump and rebound. This enables the user to make them work perfectly with the chosen springs.

Bump: this is the speed at which the damper compresses, ie "goes down" when you corner.

Rebound: this is the speed at which the damper decompresses, ie "comes back up"

Too little bump will give a lot of roll.
Too little rebound will make the car come back up too quickly and give bad control.

Too much bump will make the ride too hard and put too much stress on the damper.
Too much rebound will make the car "jump".

 

Dual Tube vs. Monotube Dampers

A main damper characteristic is its tube design. Dampers can either be dual tube (most common design, OEM design) or monotube design.

Let's take a look at how these two technologies work and what they mean to the user in terms of ride comfort, road holding ability and efficiency as well as durability.

A. Dual Tube Dampers

This is a dual tube (or twin tube) damper.

It works with gas in the upper chamber and oil in the lower chamber. When the piston rod moves in (compression), part of the oil flows from the lower working chamber through the piston valve into the upper working chamber. A quantity of oil corresponding to the volume of the piston rod is pushed through the base valve into the equalization chamber. When the piston rod retracts (rebound), the piston valve takes over the damping function, while a quantity of oil equal to the volume of the retracting piston rod flows back through the base valve.

Gas pressure is relatively low (between 5 and 10 bars).

Advantages of this design: high ride comfort (low friction)

Disadvantages: the oil flow will cause oil to heat up and foam, causing wobbly dampers and thus highly reducing suspension efficiency.

B. Monotube Dampers

Here's a monotube damper

Oil and gas are strictly separated from each other by the movable separating piston. The damping valves for rebound and compression are located on the piston. Gas pressure here is between 20 and 30 bars.

Compression stage: When the piston rod moves in, a quantity of oil equal to the volume of the piston rod compresses the gas chamber by means of the movable separating piston.
REBOUND stage: When the piston rod retracts, the gas chamber expands and pushes back the separating piston.
Damping takes place in both directions via the multi-step piston valve.

Advantages: precise, long lasting handling, no oil foaming.

Let's take this technology one step further. If we move part of the gas reservoir (also called container or canister) to a remote location, in addition to better gas cooling (after all, we're talking about nitrogen compressed under 20 to 30 bars pressure!),we can now adjust the gas pressure to adjust the damping speed.

As you can see on the picture below, the principle is simple: basically, part of the gas damping action is relocated to a remote gas canister allowing fine tuning of the suspension.

The damping speed should be adjusted to suit the spring, ride height, road condition, tyres and personal preference. For fast road use on good road tyres, you will typically be in between 30% and 50% of the damper's capabilities. For track use (or with better tyres), a click or two on the compression setting button of the reservoir will give better response, less roll and less comfort for competition type use.

Here's a picture of Öhlins shock absorbers with separate, remotely located gas reservoirs, installed onto the bulkhead of my Evo 6.

On the left hand side of the left gas canister (and on the right hand side of the right gas canister), you can see a small black button. This button can be turned clockwise to increase the compression, or anticlockwise to decrease it. Changing the compression is a matter of seconds. This way, the suspension can easily be adjusted when undertaking camber adjustment, tyre change or for other use such as some track day fun.

 

So why is all this suspension stuff so important?

Well, as unbelievable as it may seem to the novice, a perfect suspension setup can compensate for lack of engine power or even brakes, around a track. A well suspended standard car will be faster around a track than one with 50 bhp more (talking about 200 bhp or more here) or one with better pads. Simply because traction is so much better and cornering speeds achieved much higher.

Here's a quote from my friend Pierre César Baroni, 1993 European Rally Champion:

" The suspension is the very BASIS of the competition car"

His Delta Intgrale wasnt the one with the best engine, nor the one with the most efficient brakes; it was simply the one with the best set up suspension.