In the modern world of short track racing for both dirt and asphalt competition, shocks have become one of the most important tuning tools we have. They complement the current setups, especially the radical soft spring setups. And so, we complete our trilogy of shock technology articles with the final installment on how to tune the transitions.
This information is useful whether you are running more conventional setups and critical for the more radical ones. Think along as we discuss how shocks affect the speed of movement and the load distribution at the four corners of the car as we transition from high speed to minimum and then to high speed again.
To get the low and flat attitude at the front shown here, you need soft front springs, a s
This sketch shows how increasing or decreasing the compression or rebound at each corner c
This is a graph generated by a shock dyno that shows a relatively normal shock. The reboun
We have learned that shocks regulate the timing of movement of the four corners of our race car. Matching the shock rates to the spring rates on a conventional setup is fairly simple and can be done with off the shelf shocks. Matching the shocks to non-conventional setups can be a bit tricky. Let's take a look at how we can improve our overall setup package by helping our car negotiate the transitional phases of the racetrack.
Entry Tuning with Split-Valve Shocks
If we split the front shock compression rates with a LF 5/4 (5 rebound and 4 compression) and a RF 5/5, then, while the suspension is in motion due to weight being transferred on to it, the RF suspension will move slower than the LF suspension. Additional weight will be transferred onto the RF and LR tires causing a momentary increase in the crossweight percent in the car. This obviously tightens the car.
It's important to note that contrary to some opinions, the load transfers almost immediately when a force is presented to enact that transfer. As we brake into the corner, the load transfer happens quickly. If on entry we transfer 300 pounds from the rear to the front, the 300 pounds goes to the front in an instant.
The distribution of that 300 pounds between the two front wheels, while the suspension is assuming a new attitude that will support the additional weight, will depend entirely on differences in stiffness of the suspension systems at all four corners. Stiffness is defined as the resistance to movement influenced by the shocks and springs.
Reasoning out the effect of load transfer onto the front suspensions that are dissimilar in stiffness, the slower moving (or stiffer) corner will momentarily retain more of the transferred load while the suspension is moving to a new attitude to support the added weight. If the RF suspension is stiffer than the LF suspension, then both the RF and LR tires will support more of the transferred load.
Crossweight is defined in short track racing as the percent of the combined RF and LR weight divided by the total vehicle weight. If the crossweight percent increases, then the car will be tighter on entry and the car might be faster if that is the desired effect. This is exactly why it has been said that a stiffer RF shock will speed up load transfer to that corner. In truth, some of the momentary load that has been transferred onto the RF due to that corner being stiffer than the LF corner will return to the LF tire as the car reaches steady state or a steady ride height at mid-turn.
Here we see how increasing or decreasing the compression or rebound at each corner can loo
By using split rate shocks between pairs on each end of the car, we can tighten the car on
If the car is already tight on entry, after having eliminated common causes of tight entry such as rear misalignment, rear steer or brake bias issues, then an opposite effect can be utilized. If we increase the compression of the LF shock and/or increase the spring rate on that corner (which is usually a good idea for flat tracks), then we can effectively reduce the crossweight in the car on entry while the suspension is in transition by loading the opposite diagonal, the LF and RR. As one diagonal goes up in percentage of supported weight the other goes down.
We can also work with the rear shock rebound rates to help effect changes in load distribution and corner entry characteristics. To neutralize a car that is tight on entry, a stiffer rebound setting in the LR shock and/or a softer rebound setting in the RR shock will cause more of the transferred load to be taken from the LR than the RR tire during the transitional period. This too causes a decrease in the RF and LR weight distribution percentage which loosens the handling momentarily while the suspensions are in motion.
Modern soft spring setups use a much lower compression setting due to the high spring rate of the bump. We can still utilize this method by creating a compression split. The numbers will be lower than with a conventional setup, but still effective.
Once the shocks are firmly on the bumps, the load distribution will equalize and the advantage of shock compression split will be nullified. If the shock rebound settings are high enough, the shock will never leave the bump and no amount of compression split will work.
Exit Tuning Using Split-Valve Shocks
Corner exit performance that utilizes the shocks is primarily tuned by splitting the compression settings in the rear shocks and/or the rebound settings in the front shocks. A stiffer compression setting in the LR shock will load the LR and RF corners as load is transferred to the rear while the rear suspension is in motion to tighten the car with more crossweight percent. A stiffer shock in rebound at the LF corner can help accomplish the same effect by causing a slower movement of that suspension and a more rapid transfer of load off of that corner which in turn increases the percentage of load supported by the RF and LR tires.
With the soft spring setups, the rear rebound settings can really help a car that is otherwise limited in adjustments. If the RR spring is very stiff, and this is both common and mostly unnecessary, there will be a loosening effect on acceleration when load transfers to the rear.
The stiffer RR spring will take much of the load transfer from acceleration until the car is settled and even beyond. What helps is to increase the stiffness of the LR shock compression and reduce the compression of the RR shock. This serves to equalize the resistance to compression due to load transfer.
The term "tie-down" is often used to refer to a shock that has an unusually high resistance to rebound. If the rebound rates are higher for both left side shocks than those of the right side shocks, then as the car turns left (especially with quicker turning rates associated with smaller radius turns), the tendency for the left side suspensions to quickly rebound as load is transferred from the left side to the right side is reduced.
If we can stop the sudden motion, then we can keep the left side down on initial turn in and the chances are that the whole attitude of the car through the middle of the turns will be lower. A lower center of gravity (CG) means less load transfer off the left side of the car and more retained left-side weight. For asphalt stock cars and dirt cars on higher banked tracks with grip, a higher left-side weight means more equally loaded tires, left to right, and more traction. The opposite is true of dirt cars on slick tracks.
The reverse term, or "easy up" shocks, are used to help raise the suspension quickly which does also raise the CG of the sprung mass and a higher CG promotes more load transfer. Drag cars use this effect on the front of their cars to promote more load transfer to the rear tires for added traction.
On dry slick dirt tracks, teams can utilize less rebound in the left side shocks and in the front shocks to promote load transfer to the right side for better side bite and to the rear for better traction off the corners.
Adjustable shocks can be run on a dyno and graphed to show the rates at various settings.
The trend in asphalt Late Model racing is towards softer settings on compression and highe
If the shock rates are arranged in a certain way, the load distribution will not be advers
Putting All of This to Use
In order to utilize the configurations we have discussed here, we must be able to use a range of different rates of shocks in order to find the right combination for our car at a particular racetrack for a particular setup. For a team that races at only one track, the process is fairly simple.
You would experiment to find the fastest set of shocks and ones that suit the driver's style and stick to those. For teams that travel to different tracks, some changes will be necessary if the setup needs to change and/or the track layout is different from track to track.
Most shock experts agree with certain basics, such as:
1 The shock package should be softer overall when racing on dirt and when the track is flatter when on asphalt for the conventional setups.
2 Get your basic setup close to being balanced before trying to tune with shocks. Shocks can't solve basic handling balance problems.
3 Higher banked tracks require a higher overall rate of shock as opposed to flat tracks. This is because of the higher speeds and the extreme amount of downforce.
4 Shocks that are mounted farther from the ball joint should be stiffer than if they were mounted close to the ball joint. That is because with each inch of travel of the wheel, the shock mounted farther away will move at a lesser speed which means less resistance in both rebound and compression.
5 Tune entry performance first. If there are no entry problems, make small changes if you want to experiment to see if entry can be improved. Entry problems include a tight car or a loose car. By far the worst problem would be the loose-in condition. Nine times out of 10 this is an alignment problem and not shock related.
6 Tune exit performance last. If there are no exit problems, don't make any significant changes. Exit problems can include a car that pushes under acceleration or one that goes loose under power. Be sure that you do not have a tight/loose condition where the car is basically tight in the middle and goes loose just past mid-turn. This is fixed with spring rate changes, Panhard bar adjustment, and more.
7 On dirt racetracks, reduce rebound settings on the left side and decrease the compression rates on the right side for dry slick surfaces to promote more chassis movement. This helps to maintain grip as the car goes through the transitional phases of entry and exit.
8 On asphalt tracks, once the car has been tuned with shocks for optimum entry and exit performance, increase the overall rebound rates a small step at a time, especially on the left side, to possibly increase overall performance. This is especially good for low to medium banked racetracks. For highly banked tracks, the added rebound is not necessary or advisable.
9 For the soft spring setups on asphalt, the whole shock package is much different than when running conventional or soft conventional setups. The bump rates (either bump rubbers, spring rubbers, coil bind, or bumpsprings) will be very high and the shock rebound rates must match those high rates in order to control the device.
A bump that is used in the 1,000-ppi spring rate range will need a shock that is rated at 1,000 ppi at around 3 inches of movement per second. Usually, the low speed rate of the shock will be comparatively high too and often we see a "nose" rate of between 500 and 800 ppi or more at close to zero movement.
This was considered extreme tie down a few years ago and we can see where there is very li
This is a graph of the shocks we used in our bump spring testing. We can see the “nose” wh
A Closing Caution
The suggestions provided here are representative of trends that can enhance your handling package. Before any of this can work, the setup must be balanced, the steering characteristics must be ideal and the car must be aligned properly. If not, you will probably chase the setup and experience a lot of frustration and expense.
Shock tuning is the last thing to experiment with in order to try to increase your race car's performance, but it is nonetheless a necessary step in finding the ideal total handling package. That said, before you set up your car and chose your shocks, evaluate what you will need to match the spring rates you will run.
If you're experimenting with the soft spring setups, consult your shock expert so that you can match your shocks to the setups. Most racing shock companies have technicians who are very familiar with those setups and can advise you in the best rates to use to match your bumps.