To break through the mystery of the racing shock and how it influences handling, the best way to view a shock, or damper, by its proper term, is to simply view the shock as a timing device.
In this video we outline the topics discussed.
Shocks allow the chassis tuner to decide how fast in the corner weight is transferred.
Whereas track width, center of gravity and cornering force control how much weight is transferred in a corner, (see previous video on our channel where we break down the relationship between Weight Transfer and Roll)
And the springs control where weight is transferred, front relative to the rear.
Driver input controls the timing and when weight is transferred, and shocks control how fast or how slow that weight is transferred. Either delaying or speeding up the weight transfer.
Tuning with shocks is only to be done after the overall setup on the car is close. Shocks will not help fix major chassis setup issues. We will talk about this more coming up.
Basic Operation of a Shock/Damper
Shock absorbers work in two cycles – compression and rebound.
Compression, or Bump, as it is also called, such as under roll on the loaded side and when hitting a bump.
And Rebound such as coming out of roll on the loaded side and the backside of a bump.
Shocks resist the oscillations of the spring and chassis by use of friction of a piston with valves moving through a hydraulic fluid in a cylinder.
By using different valves, the shock designer can change the “rate” of the shock. Rate meaning either how much or how little the shock resists movement.
Firm and less firm, and increase/decrease are how it is commonly referred to. More stiff, or increase the rate, means the shock will respond slower.
Less firm, or decrease the rate, means the shock will respond sooner.
Shocks are Shaft Speed Sensitive
The speed at which the shock piston moves through the hydraulic fluid also affects how much the shock resists movement. The rate of the shock changes as piston velocities change.
Shown is a common shock dyno plot that correlates shock velocity with force. Force is shown on the y-axis and shock velocity on the x-axis. Bump forces are shown above the zero line, and rebound shown below the zero line.
Your shock manufacturer can change your valving if you know what forces you need based on the track surface and the shaft velocities you’ll see at that track.
The shock tuner can tune for low speed movement such as under roll on the 0 – 5 inches per second range.
As well the shock tuner can tune for high speed shock velocities such as when hitting a bump, and these are on the range of 6-15 inches per second and above.
Low speed shock valving is the primary tool available to the chassis tuner to influence handling.
Compression damping affects how slowly or quickly weight is applied to a tire.
Rebound damping affects how slowly or quickly weight is removed from a tire,
Any time the driver is moving the steering wheel or applying brake or throttle the shock will influence handling.
When the car is fully loaded in the corner and weight is fully transferred, such as mid-corner, the shocks no longer have any great deal of influence on handling.
Shock Movement in a Right Hand Corner
On turn-in on a right turn, the shocks on the left front and right rear will be moving the most and will have the biggest effect on handling. The left front shock will be in compression, and the right rear will be in rebound. On exit, under throttle, these forces flip and the left front will go into rebound and the right rear will go into compression.
Shock Movement in a Left Hand Corner
For a left hand turn the opposite will be true. The right front and left rear will be moving the most and will have the biggest effect on handling. The right front shock will be in compression, and the left rear will be in rebound. On exit, under throttle, these forces flip and the right front will go into rebound and the left rear will go into compression.
Different Types of Racing Shocks
Racing shocks come in three types. Single adjustable, double adjustable and triple adjustable.
For single adjustable compression and rebound forces are adjusted the same. If rebound is made more stiff, so will compression. If using shocks to correct for a specific issue on the track, you may induce issues at other parts of the track where none existed before using a single adjustable shock.
A double adjustable shock allows the chassis tuner to adjust compression and rebound forces independent of each other. Greatly enhancing tuning options.
A triple adjustable shock allows for adjusting compression and rebound forces independent of each other adjusting as well as adjusting for low-speed and high-speed shock velocities independent of each other. Further enhancing tuning options. Great when going from a smooth track surface to a more bumpy track surface.
Using Shocks to Fix a Car with Slight Corner Entry Understeer
For a specific case, let consider a car with a slight understeer on corner entry. Where it occurs in the corner is crucial. If the chassis setup is close and the driver has been eliminated as being the source of the problem, we can look at making some adjustments with the shocks to correct for this.
For understeer the front tires are losing traction.
If the understeer occurs on corner entry we can decrease front compression, putting weight to the front tires sooner.
If the understeer occurs mid-corner we can increase front rebound keeping weight on the front tires for a longer period of time.
If we have a single adjustable shock this creates a dilemma because increasing or decreasing rebound will also increase or decrease compression. As stated before, if making the adjustment to correct for an issue in one specific corner, you may induce problems in other areas of the track where previously none existed.
Going to a double adjustable shock eliminates this problem.
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When to Tune with Shocks
Before tuning with shocks, the rest of the chassis needs to have a pretty close setup. Tuning with shocks will not fix major issues and is only to be done as a “fine tune” after the rest of the car’s setup is pretty close. Don’t expect much more than a 0.1 to 0.2 or so per lap improvement in lap time though from shock tuning. A good set of shocks such as the premier racing shock from AST CAN make the car more drivable and help improve handling in certain portions of the track.
Before tuning with shocks make sure:
- Caster, camber and toe are close.
- Tire pressures are close.
These two adjustments help maximize the contact patch of the tires which is our primary goal in chassis tuning and needs to be completed first.
- Cross weight percentages are close.
- Spring rates are close.
If you try and tune with shocks before any of the above is close you are aiming at a moving target.
When making a change with shocks go 2 clicks so the change is noticeable. Going one click the change may not be noticeable. If you saw on improvement, go two more clicks. Continue until the change is worse, then back off one click.
If running data you can segment out the track and notice where you see improvements or where the change made things worse. If you are not running data you can feel the difference in your seat and hands and engine rpms on exit, and obviously, in your lap times.