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Compression and Rebound Adjustment on Coilovers

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Compression and Rebound Adjustment

Most coilover systems have adjustment for compression and rebound. Depending on the model you have, this can be done with a turn of one dial for overall adjustment (compression and rebound together) or fine tuning through multiple adjusters. Compression is essentially the shock’s ability to compress under load. Rebound is essentially the shock’s ability to retract after compression. Both actions are a cause and effect sequence that affects car control and ability.

First determine your type of coilover and then click below for details on tuning. Please do not confuse the amount of “click”adjustment on a dial (15-way adjustable with STANCE coilovers, 30-way adjustable BC Racing coilovers, etc.) with the actual number of adjustment dials for different versions of coilovers that are listed below.

Adjustment should be done per axle or on all four shocks, never on just one corner. It is also good practice to make adjustment in small increments and testing to see if the effect was positive. We recommend to start at a good neutral position and then adjust accordingly. In aggressive driving situations, proper adjustment can make a world of difference for performance.

 

1-Way Adjustment Coilover (single dial)

This system is found on 99% of coilover systems out there and is usually for street/track use. These coilovers are meant to meet the desire of overall adjustment with one turn for increased car performance or to reduce suspension movement to prevent tire rub with a lowered car.

To adjust, simply rotate the the dial clockwise to reduce shock movement (make stiffer) or counter clockwise to “free up” shock movement (make softer).

Adjustment Guidelines

  • If you feel that the car has too much body roll and feels sloppy, you would increase stiffness.
  • If you feel like the car does not have enough movement and the tires lose traction under cornering, braking, or acceleration, you may need to reduce stiffness.
  • Usually in rain or low grip situations less stiffness is desirable to delay tire loading upon initial roll.
  • In dry, high grip conditions, adding stiffness will load the tire sooner upon initial roll, increasing platform stability.
  • If you experience tire rub under load and bump situations, stiffness will need to be increased to prevent it. This may hinder car performance if the setting required is too stiff and doesn’t allow enough suspension movement. You may want to consider raising the car during spirited driving to allow proper suspension travel.

Below are a few basic scenarios for your trackday/autocross. These are situational and many other factors play into them. But this is an example how you can lessen them with adjustment:

Car under-steers into a corner

  • POSSIBLE REASON: The front tires are not getting enough grip because they cannot load properly.
  • CAUSE: Coilovers are set too stiff.
  • FIX: Reduce front axle stiffness and/or increase rear axle stiffness.

Car over-steers into a corner

  • POSSIBLE REASON: The rear tires are not getting enough grip because they cannot load properly.
  • CAUSE: Coilovers are set too stiff.
  • FIX: Reduce rear axle stiffness.

Car is sliding around a lot and losing traction

  • POSSIBLE REASON: The tires are not getting enough grip because they cannot load properly.
  • CAUSE: Coilovers are set too stiff.
  • FIX: Reduce overall stiffness.

Car feels sloppy and has a floating feeling

  • POSSIBLE REASON: The tires are being overloaded with weight transfer or there is too much body roll.
  • CAUSE: Coilovers are set too soft.
  • FIX: Increase overall stiffness.

2-Way Adjustment Coilover (double dial)

2way-shockgraph

2-way adjustment includes, as with BC Racing ER Type and STANCE  Pro Comp 2 systems, a separate dial for dampening and one for rebound. This will allow you to fine-tune your coilover system for the track. Both drag cars and circuit cars can benefit from this ability. Street cars will only see minimum benefit with anything more that a 1-way adjustable system, but it never hurts to have style points.

Compression Guidelines

  • Start out at full soft (turn the knob counter-clockwise until it stops) and increase until the car feels too stiff or becomes harsh and looses traction. Decrease from this point until the harshness goes away and the car is not upset by bumps.
  • Usually in rain or low grip situations less compression is desirable to delay tire loading upon initial roll.
  • In dry, high grip conditions, adding compression will load the tire sooner upon initial roll, increasing platform stability.
  • In pitch situations on smooth surfaces under braking, increasing compression will help load the tires for entry or mid corner.
  • If the chassis feels like its moving around too much relative to the track, increase compression to firm up the chassis and give it a crisp feel. This will also give a better feel of the car, resulting in higher confidence for the driver.
  • Too much compression will create a lack of grip during directional changes, won’t allow to put the power down and lack grip on turn in.
  • If the tire begins bouncing under braking , usually an increase in compression will calm this down.

Rebound Guidelines

  • Start out at full soft (turn the knob counter-clockwise until it stops) and increase until the car becomes stiff and feels loose on corners. Decrease from this point until car feels stable and balanced.
  • Rebound adjustment is used to add more stability and control the amount of body roll. By increasing it, stability will be enhanced. Decreasing it will allow more movement in the car but will result in a little better tire wear.
  • Less front rebound allows weight transfer to the rear under acceleration. This will affect rear tire grip, especially under acceleration out of a corner.
  • Less rear rebound allows for weight transfer to the front under braking and turn-in. This can affect initial corner turn-in tire grip and adjustment can help correct under-steer on initial corner entry.
  • Too much rebound can cause the shock to pack down over series of bumps. You will recognize this as too stiff and think its needs less compression.

3-Way Adjustment Coilover (triple dial)

3way-shockgraph

3-Way adjustment includes, as with STANCE  Pro Comp 3 systems, a separate dial for rebound, low speed compression, and high speed compression. This will give you  even more tuning ability than the 2-way.

It is important to note that low and high speed compression adjustments will have affect on one another. If the low speed is at “soft” setting, the high speed adjustment will be lessened. If the high speed is set at “soft”, the low speed range will be lessened. When big adjustment is made in high or low speed, the change will affect the other in a small percentage.

Low Speed Compression Guidelines

  • Adjusts low speed shaft velocities (corner entry/exit, power down). Start out full soft (turn adjuster counter clockwise until stops). Add more low speed compression until car feels too stiff or becomes harsh and looses traction. Decrease the low speed compression until harshness goes away.
  • The biggest advantages with low speed adjustment is looking at the chassis in the plane four wheels in relation to chassis movement. This translates into roll and pitch and how quickly weight is transferred to each corner in order to load the tire sooner or later, depending on track conditions.
  • Usually in rain or low grip situations less low speed compression is desirable to delay tire loading upon initial roll.
  • In dry, high grip conditions, adding low speed compression will load the tire sooner upon initial roll, increasing platform stability.
  • In pitch situations on smooth surfaces under braking, increasing low speed compression will help load the tires for entry or mid corner.
  • If the chassis feels like its moving around too much relative to the track, increase low speed compression to firm up the chassis and give it a crisp feel. This will also give a better feel of the car, resulting in higher confidence for the driver.
  • Too much low speed compression will create a lack of grip during directional changes, won’t allow to put the power down on slower corners and lack grip after initial turn in.

High Speed Compression Guidelines

  • High speed adjustment must be made by judging the bumpier sections of the track. If the car feels too stiff, decrease high speed compression. If the car feels too soft, increase the high speed compression.
  • If the tire begins bouncing under braking , usually an increase in high speed compression will calm this down.

Rebound Guidelines

Same as 2-way rebound, see above.

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