As you drive a corner, your control inputs are constantly transitioning so that you can swing your car’s acceleration vector around at the right rate for your current location to produce the minimum segment time through that corner. Your acceleration vector is straight aft while you are braking in a straight line, then it swings toward the center of the corner as you add steering and reduce braking. The acceleration vector continues to swing forward from the corner center toward the next straight as you reduce steering and add throttle. At the track-out point, your acceleration vector has swung through 180 degrees from straight aft to straight forward. In response to these driver input transitions, the suspension of your car constantly transitions, from braking dive to cornering roll to acceleration squat.
Springs, anti-roll bars, and downforce balance affect what your car does in steady state cornering conditions, but there is an additional, very important influence at work during corner transitions. That influence is suspension damping. Damping is a key factor in tuning the cornering balance of a racecar, and cornering balance is one of the key factors in determining how fast your racecar can be driven. This article will describe the damper behavior at work during only one of the many possible kinds of corner transitions, and why increasing or decreasing the damping force changes how a racecar behaves. We don’t have room here to discuss all of the variables. To get the full story that covers all of the possible types of corner transitions, pick up a copy of my book, “Think Fast – The Racer’s Why-To Guide to Winning.”
WHAT’S A DAMPER?
A damper is the accurate term that describes the suspension component that is more commonly called a shock absorber. That is because the suspension springs and tire sidewalls actually absorb shocks from the road, while dampers convert the kinetic energy of shock absorption into heat as the suspension moves up and down after a shock. The design and the behavior of an automotive suspension damper has evolved and become quite complex to achieve an acceptable compromise among the many conflicting requirements imposed on it. Those requirements include producing smooth ride quality, minimizing tire force variation over rough pavement, providing immediate and repeatable response to the driver’s control inputs, and minimizing movement of the sprung mass in heave, pitch and roll.
DAMPER SHAFT SPEEDS
One of the most effective ways to change the way that your car behaves on the race track is by changing how much force your dampers produce in the low shaft speed range. The speed that we are talking about is the rate that the damper piston and shaft moves through the hydraulic fluid contained in the body of the damper. High shaft speeds are seen in response to rough pavement and curb strikes, while low shaft speeds are the result of suspension movement caused by driver input transitions. The low shaft speed range is from zero to roughly 5 inches per second, while the high shaft speed range is anything faster than that. It is possible, and quite common, for low shaft speed and high shaft speed events to occur simultaneously, but the response of a damper during these simultaneous events is highly dependent on both the design and the condition of the damper. This is one aspect of well-developed racing dampers that sets them apart from mass production road car dampers.
DIAGONAL SUSPENSION MOVEMENT
Put on your thinking cap and stick with me here. Things are about to get complicated and long-winded. The key to understanding how and why damper adjustments affect handling is in understanding what happens during diagonal suspension movement. The one example of diagonal suspension movement that we will discuss here is the transition from straight-line braking to cornering. During this transition, weight is transferred away from the inside front tire and toward the outside rear tire. The suspension moves in response to this weight transfer, of course. The largest and fastest movements are the inside front damper moving in the rebound direction and the outside rear damper moving in the bump direction. The other two dampers also move some, but not as far and not as fast. For the purpose of damper tuning, we can consider those two dampers to be stationary during this transition. That places the focus on the inside front and outside rear dampers, because they move in response to diagonal weight transfer.
EFFECTS OF DAMPER-INDUCED WEIGHT TRANSFER
During our cornering transition example, we have two dampers moving in opposite directions, on opposite corners of the car. Why do we care about this? Here is why: The horizontal forces produced by all four tires determine the cornering balance of the car, and dampers that are moving change the vertical loads on the tires. So, damping forces affect the car’s cornering balance during transitions.
DAMPER TUNING FOR IMPROVED CORNERING BALANCE
Let’s say that the car in our transition example has a lot of rebound damping dialed in to the front dampers. During the braking-to-cornering transition, the strong rebound damping will act to reduce the vertical load on the inside front tire while the dampers are moving. The inside front damper tries to lift its tire off of the ground. That load has to go somewhere, so it is distributed among the other three tires. During this transition, strong front rebound damping has the same effect as a stiffer front anti-roll bar: more understeer caused by a larger difference in vertical loads applied to the two front tires.
Interestingly enough, more rear bump damping has the same effect on cornering balance as more front rebound has during the transition that we are discussing. If the car has too much understeer during the braking-to-cornering transition, then either reducing front rebound or increasing rear bump will act to reduce that understeer. This is one example of why externally adjustable dampers can make a racecar faster.
Because there is more than one option available to change the cornering balance in this and other types of cornering transitions, it is possible to use bump or rebound damping adjustments at the front or rear to tune the cornering balance through many combinations of transitions on each race track. With selective use of damper adjustments, it is possible to improve the car in more than one key corner on each track. My experience in adjusting cornering balance according to the diagonal weight transfer tuning technique has shown it to be amazingly effective in changing how the car behaves. Damper adjustments are just as effective as spring and bar changes in tuning the dynamic cornering balance of the car.
Although externally adjustable dampers are not absolutely necessary to the process of using damper tuning to change the cornering balance of a car, they sure do make it easier. When you are shopping for racing dampers, make sure that the external adjustments primarily affect low speed damping. If they don’t, keep shopping elsewhere.
When you have adjustable dampers on your car, adjust them! My policy at the track is that every time the car comes to a stop, I make one setup adjustment. That makes every outing a development opportunity, and that makes the most effective use of the time and money that is spent at the track.
Low speed external adjustments are only one aspect of damper tuning. External adjustments are only useful if the rest of the damper build is close to the right range for your application. Racing dampers can be assembled to produce anything from very soft to very stiff damping as a result of different internal component selections. The external adjustments can only change the damper curve a relatively small amount from the curve that results from internal component selections. Before you buy any hardware, it is an excellent idea to talk with a racing damper expert about the specifics of your car, your setup information, your tracks, your expectations, and your driving style. That is the best way to ensure that your damper build is close to the right range for your car. This level of customization is standard practice for racing dampers, even at the amateur level. Of course you should expect to pay for the level of expertise that is involved.
One alternative to externally adjustable dampers is an inventory of non-adjustable damper sets with different valving in each set. Another alternative is multiple damper mounting locations on the car, so that the motion ratio of the damper is different in each location. The downside to that approach is that both bump and rebound damping will either increase or decrease together when you relocate them. A rather risky alternative is buying used dampers that were tuned for a different car. Unless that car is very similar to yours in all respects and it handled really well on those dampers, the customization of internal components is unlikely to be close enough to produce the right damping range for your car.
There are three- and four-way externally adjustable dampers available on the market, and a variety of more advanced options. Those additional adjusters change high speed bump and rebound damping. Because the handling behavior of a racecar is less responsive to high speed damping adjustments, those additional external adjustments are mostly useful in eliminating the need to change the internal components for track types that are dramatically different from the ones that your car has been developed for. That is a time saver for professional racing teams that run on a wide variety of track types on a schedule that alternates track types frequently, but this level of adjustability is rarely needed for NASA racers. Two-way adjustable dampers with the right internal valving are all that you will ever need.
Damping adjustments are a surprisingly powerful way to influence the cornering balance of your car during cornering transitions. If you have never made a damping adjustment on your car, there is a whole new world of tuning out there waiting for you. To make the best use of damper adjustments, it takes an accurate recollection of how the car behaved in every segment of every corner during your last outing, and it takes a good understanding of the diagonal weight transfer tuning technique to determine what the next damper change should be. Damper tuning is one area where thorough understanding and clear thinking produces better performance.