What is a Damper?
A damper is an oil filled tube with a piston inside. The piston moves through the oil, passing the oil through small precise holes and past a sprung shim, at a certain designed speed.
A damper consists of:
- A main body
- A piston with precisely machined holes through it
- Adjuster needles
The main body is the housing of the damper and often contains an external thread to allow the spring base to be wound up and down to adjust pre-load and ride height.
The piston connects to the chassis and inserts into the body and moves through the oil during damper operation.
The shims sit on top of the damper and flex when oil passes through the piston to allow the oil out. These are usually tuned to the spring rate and are an important factor to get right when specking or designing a damper system.
Adjuster needles are pointed needles that screw in and out of the holes to allow more or less oil to pass through the piston and these are used to control the oil flow and therefore the bump and rebound characteristics of the damper.
The oil is the fluid used to pass through the damper and is chosen with a set viscosity to flow through the holes and past the shims at a certain controlled rate.
The nitrogen is a non-reactive gas that is used to pressurise the oil within the damper to a set pressure to make the damper operate as designed. Nitrogen is also used within external reservoirs to keep the pressure in the reservoir up so it can supply the damper body with no delay when required. The nitrogen can also act like a spring from within the damper to smooth out the damping effects for high speed impact.
The Purpose of a Damper
The damper’s job is to control the motion of the spring and manage the weight transfer and shock loads of the car. Without a damper, the coil spring would oscillate to the end of time, once disturbed, which is not ideal when you are trying to maintain a constant contact patch to increase grip to a maximum. Therefore, the damper controls how much the spring can oscillate and returns it to a stationary position a fast and efficiently as possible once the spring has done its job.
Another purpose for the damper is controlling how fast the spring is allowed to compress and extend. This is referred to as bump and rebound and is very important. Controlling how fast the damper can compress or extend controls how much the car rolls in and out of corners which is very useful to tune understeer/oversteer out of the car.
Another purpose of the damper is to act as a shock absorber. In categories like rallying this is even more important where the ground is uneven and wheel needs to absorb as much shocks form the ground as possible to not jolt the car up. In order to absorb high speed jolts on a track but maintain a stiff suspension set up for cornering, 3 way adjustable dampers really come into their own.
When Does a Damper Work?
A damper is an acceleration reactive component. This means that it is only effective when the damper accelerates or decelerates. If it is operated at a constant velocity it will not work effectively.
Put simply, a damper only works when the car enters a corner, exits a corner or experiences a bump or droop in the road or the car lifts up or down like in a bump or a crest on the track or due to acceleration or braking.
Therefore, it is not active when the car is driving smoothly down a road in a straight line or in the middle of a corner when the weight transfer has fully occurred and the car is settled and cornering in one direction.
It is important to know when a damper is active, such as corner entry and exit, so they can be tuned and adjusted correctly according to driver feedback and where on track the car needs adjusting for.
Bump and Rebound Adjustment
The two most common adjustable aspects of a damper are bump and rebound. Bump adjustment is adjusting how fast the damper can compress. Rebound adjustment is adjusting how fast the damper can extend after the compression.
The bump forces are where the wheel moves vertically up in the arch and compresses the spring and damper. These forces come from lateral loads and the mass of the car. This is adjusted if the car is leaning too much on corner entry and exit or if it feels as though too much body roll is occurring. Alternatively it can be adjusted based on how the car rides over bumps such as apex curbs or if the car is bottoming out or lands too aggressively after driving fast over a crest.
The rebound forces are based on the forces from the spring extending on the damper. When a spring compresses it is usually a fast process and the vertical displacement is often absorbed within the damper. If the spring was allowed to return to its normal length with the same speed as it compressed then it would slam the wheel back towards the floor resulting in a notable jolt to the car which is unsettling for the driver and the grip.
Therefore, rebound adjustment is key to control the rate at which the spring and damper are allowed to extend. This is most ideal for tuning how a car exits a corner when the car rolls back to centre as the lateral load reduces. A smooth return is important to not overload the tyres and reduce the grip of the car. Another area is where a car rides a curb or lands from a jump/rise over a crest and needs to rise back to ride height. If this is done slowly and controlled it is much better for driver confidence and maintaining grip at the tyre.
1, 2 , 3 and 4 Way Adjustable Dampers
Dampers and coilovers are often adjustable to allow the user to tune the suspension directly to their car, surface and track speed.
If a damper is 1 way adjustable it tends to be only the rebound that can be adjusted. This is because the compression is controlled mainly by the spring rate of the spring and the mass of the car compressing it so is often a controlled compression. However, the spring will extend much faster than it compresses as it extends against the smaller mass of the wheel assembly which results in a much faster aggressive extension. Therefore, being able to adjust and manage this is more important to manage grip and driver feedback than adjusting bump.
If a damper is 2 way adjustable then it allows the bump and rebound to be adjusted on the coilovers. This means that the valving in the damper can be changed to allow the oil to flow at different rates through the piston for bump and rebound. Therefore, it is possible to run set ups where the bump is hard so the car can corner quickly without much body roll and rebound is hard so the wheel extends back to the ground in a controlled manner also. Having bump and rebound adjustment is an important minimum for serious track user or motorsport categories as they are both required to finely tune the response and handling of the car.
If a damper is 3 way adjustable then it allows the rebound to be adjusted and the high speed bump and the low speed bump to be adjusted. A track car needs to be very stiff to prevent the body from rolling on corner entry as much as possible if it has the grippy tyres and aero to match the set up like in most single seater categories. However, when the car encounters a sudden bump such as a kerb or a pothole in the track, it can make the car lift up in the air and lift the tyre off the ground due to the set up being so stiff. This is bad for grip as the tyre is not able to generate any grip in the air. One way to combat the sudden jolts is to soften the suspension to account for kerbs, however this means that the cornering capabilities are limited due to the increased body roll and mass transfer during cornering. This is where a 3 way damper becomes essential.
The high and low speed bump adjustment allows the damper to account for both scenarios and have the best of both worlds to improve the grip and speed of the car. The high speed bump settings can be set to soft so that high impact fast bumps can be absorbed by the damper and not upset the dynamics of the car. This allows the low speed bump to be set stiff so that the cornering can have a stiff set up a the speed of the damper when cornering is much slower in comparison to hitting a kerb or pothole.
If a damper is 4 way adjustable it means that high and low speed rebound can be adjusted and high and low speed bump can be adjusted. This form of damper is rare and often very expensive and is only used at the very top of motorsport where the finest details count. It is useful in a very similar way to that of a 3 way adjustable damper and works in the same way and is beneficial in the same areas expect that the high speed rebound can also be controlled. This means that there can be one rebound setting for when the car is cornering and then another rebound setting to control how the damper extends after a high speed bump situation occurs or where the damper can extent suddenly like if it leaves the ground due to very stiff settings or a jump over a crest.
External reservoirs are smaller cylinders that are attached to the side of the damper body. They are sometimes rigidly mounted to the damper body and other times are on the end of a pipe so they can be mounted in an easily accessible space. The main reason for an external reservoir is to do with heat.
When a damper works quickly, over a bumpy surface or a fast track with a lot of direction changes or kerbs, it generates a lot of heat within the damper and therefore within the oil. This is partly due to the heat from the spring working hard and also from the oil being forced through the small holes in the damper piston generating friction and heat.
Therefore an external reservoir basically increases the amount of oil within the damper without having to make the damper body any larger. The increased amount of fluid takes longer to heat up and therefore keeps overall damper temperature down. This is important because when the oil heats up, it can get hot enough to alter the viscosity of the oil. If the oil becomes thinner, it can flow through the valves more easily. This means that a stiff set up would become softer during the race which would totally alter how the car handled and it would have to be adjusted for mid race which is not ideal for a driver or race position.
The external reservoir can also be used to insert extra valving into to control the high and low speed aspects of the damper meaning that for a 3 way or 4 way damper, the valving inside the main damper body does not have to be as complex and therefore reduces the cost of the item and makes it easier to adjust and tune.