When a Sprint Cup team sits down to plan what components will be used for power and the suspension in a race car chassis they have chosen to race at a particular track, they have a variety of decisions to make concerning what power band they want the engine to perform in, what gearing they will use to transfer that power to the track and what combination of suspension parts they will select to help keep the car glued to the track as consistently as possible.
The goal of the setup specialist or engineer is to establish and maintain a consistent, and therefore reliable, tire contact patch that the driver can be comfortable with and feel confident in while he is racing. The specialist needs to determine how much rake and tilt he wants to run at a particular track and also select the truck arms, track bar, sway bars, spindles, springs and shocks, etc. to run to support that decision. And, he needs to decide what caster, camber and toe, etc. he wants to design into his setup to complement the other parts he has selected.
The correct selections and settings will, hopefully, result in a setup that will provide optimum and consistent performance throughout the race. For example, he would want to run more front wheel camber on a shorter and flatter track such as Martinsville than he would at a high-banked superspeedway like Daytona. The lateral (inertial) forces and potential body roll would be greater on the flatter and tighter turns at Martinsville than they would be on the steeper banking and sweeping turns at Daytona.
The oval track racer is constantly thinking "low and left" when he builds a race car to keep his center of gravity and therefore his roll center as low and left as possible. This will reduce body roll and help to keep all four tires firmly planted on the track's surface. He can help to achieve that goal by selecting suspension parts that will also minimize body roll. If the static weight (the weight of an object at rest) is 3,000 pounds then it is pushing down on the Earth -- because of gravitational pull -- at the rate of 3,000 pounds. If you divide the weight by four then it is pushing down at the rate of 750 pounds per tire if the weight is distributed equally -- which, on a race car, it is not.
This is where the racer tries to fool Mother Nature by redistributing what weight he can so it will push down disproportionately on the left side tires so they will have more grip in the corners when the car has inertial forces acting upon it and trying to roll it over. This is where the sway bars, track bar, shocks and springs come into play in the setup formula. Your street car probably has similarly rated springs on all four corners but a race car will have stiffer and softer springs combined to achieve a redistribution of weight when the car is experiencing inertial loads in the corners.
Keep in mind that all the selected components need to work harmoniously together to achieve the setup specialist's goal. You would not, for example, run a shock with a soft bump or compression cycle with a stiff spring (on the front end) because they would not work in concert with each other to maintain a consistent tire patch.
You might, however, run a soft spring and a shock with a softer bump and a stiffer rebound cycle so the shock and spring would compress more easily and then the shock's stiffer rebound cycle would hold the compression of the spring down longer and thus keep the nose of the car lower for a longer period of time. That is what they are doing when you hear the term "coil binding" used by crew members or analysts.
While acknowledging that the other suspension components also play an important roll in the overall setup package, we are going to concentrate on what springs and shocks can do to help the car stay hooked up to the track. If you have ever heard someone talk about "wedge" or "diagonal weight" or "cross weight" then they are referring to the weight distribution that is being accomplished via the springs that are installed in the car and what impact their relative weights or ratings are having on the car's setup.
Depending upon the type of track you are racing on the car can be either "wedged" or "de-wedged". Positive "wedge" simply means you have more than 50 percent of the car's weight resting on the right front and left rear tires. If your car is "de-wedged" or negative then you have less than 50 percent of its weight resting on the right front and left rear tires. Either way you are trying to help the car to turn better through the corner and maintain grip with the track when the inertial forces induce body roll or lateral force in the turn. If the car is too tight or too loose then the setup specialist can change springs and shocks accordingly to increase or decrease wedge in the car. He can also play with tire pressures and track bar adjustments, etc. but for the sake of this article we are focusing on springs and shocks.
Keep in mind all of these major adjustments are made at the shop during setup or during practice at the track because it is impractical to change springs and shocks during a race. Minor adjustments can be made to the springs -- such as adding or deleting partial or whole spring rubbers or, by cranking in or taking out rounds to raise or lower the spring rate during a pit stop but you can't do much else with springs and shocks once the car is on the track under competition.
NASCAR regulates the types of springs and shocks that a team can use on its car so Sprint Cup race cars cannot have exotic springs and shocks as some series allow. The springs must be of a specified height and the size and tightness of the coils that make up the spring are limited as well.
Shocks are allowed to be somewhat more exotic but again not as far out as other series would allow. This presents greater challenges to the setup specialists but they have overcome most of the problems. The COT has thrown them some new curves and they are still trying to figure out which combination works best for each track, but I'm betting that by the second part of the season we won't be hearing as many complaints about loose cars or hard tires.
Teams used to look for about three inches of suspension travel back in the good old days of stiff springs but, up until this year, Sprint Cup teams had evolved their softer spring setups to where they were getting as much as four to five inches of travel in the front so they could suck the front ends down to the track aerodynamically and keep them there for a longer period of time by using shocks with stiffer rebound valving.
They cannot achieve that much suspension travel with the COT so they are searching for new parameters.
The purpose of springs is to hold up the bulk of the race car's weight at a selected height and to absorb the bumps and compression of the suspension when the car is in motion. The weight that is supported by the springs is called "sprung weight" because it is sitting on top of the spring -- duh. The tires, wheels, brakes and suspension parts that are not supported by the springs are called "unsprung weight" because they are not supported by the springs. So what is the significance of the unsprung weight? Every pound of sprung weight equals one pound, however every pound of unsprung weight is subject to a multiplier that could make its value as high as seven or so pounds so you can see the significance of keeping your unsprung weight to a minimum.
Rotating weight -- tires, wheels, brakes, engine parts and drive line parts also have a weight multiplier but that is a subject for another day. The reason that unsprung weights and rotating weights are calculated to be heavier is because of the additional energy that is required to move them forward. In the case of rotating weight, for example, you are turning it while you are moving it forward as a mass so it requires more energy to propel it forward. The weight ratio calculation can be as high as 10 pounds to one for rotating weights. And remember, tires, wheels and brakes are both unsprung and rotating weights.
So it's not "shocking" to see that NASCAR has very strict rules designed to keep the teams honest concerning their unsprung and rotating weights because of the disproportionate advantages that can be gained. Wouldn't you like to lose one pound and look like you had lost eight or 10 pounds? I definitely would. I did lose about 150 pounds of ugly fat once when I got my divorce. Unfortunately she was totally dead weight so there wasn't any disproportionate gain.
While the springs are designed to support the car's weight and smooth out the impact of the vertical loading during the bump or compression cycle, they also work against the unsprung weight to help hold it down to the track surface and therefore maintain a more consistent tire contact patch. But if you just had springs alone then you would experience the "Pogo" effect where the chassis would bob up and down as the spring cycled or bounced and eventually settled back down. That is where the shock absorbers come into play to help stabilize or dampen the suspension bounce.
There are basically three types of automotive shocks. Originally, shocks were "progressive" meaning their compression increased at an increasing rate as the shock compressed. This was because of a simple valving system and the use of fluids (versus gas) to flow through the valve system. Then came "linear" shocks that had a more consistent resistance throughout the compression and rebound cycles, which greatly helped to stabilize them. Today's shocks can be "digressive" meaning they can be valved to increase at a decreasing rate. This allows the car's suspension to absorb a greater variety of bumps and dips and/or load changes with greater stability, which means the driver can drive it at a faster rate into the corners and still feel comfortable with how it reacts.
One of the many job descriptions on a Sprint Cup team is "shock tuner." The shock tuner is the expert who builds the shocks needed for each designated setup. This extremely important team member will insert shims, valving and spacers in various combinations to create increased or decreased bump and rebound in a shock per the selected setup's requirements. He can make a variety of adjustments to either cycle based on driver feedback and data that is gathered from testing or practice.
Shock tuners are looked upon as being something akin to witch doctors or voodoo practitioners. Nobody really knows what they do or how they do it, they just know that there is a lot of mumbo jumbo that is heard coming from the shock dyno area as they ply their craft and try to think "bass ackwards" because, when it comes to shocks and springs, up is down and down is up -- most of the time.
NASCAR dictates that each shock be filled with nitrogen gas only and that the shocks be filled at the track to a specified pressure range provided by NASCAR at each track. The shocks must be filled in front of a NASCAR official and are subject to inspection at all times during the weekend.
The shocks work in concert with the springs to help control body roll, dive and squat as the car is raced around the track. Today's teams are running softer springs with shocks that have stiffer rebounds in the front ends. They can do this by increasing the diameter of the sway bars (technically anti-sway bars) to help dampen bump and rebound plus minimize body roll. Each element of the suspension -- springs, shocks, sway bars and track bars, etc. have to work together if the team is to be successful in competition.
There is a lot of advanced suspension technology that was developed during the last five-plus years that is not directly transferable to the COT. But I am totally confident the teams will achieve the same type of development with the new car to the degree that NASCAR's rules will allow.
I made one interesting discovery while doing the research for this article: The 2008 NASCAR Rule Book is just a little more than half as thick as the 2007 Rule Book. It would appear that the COT has had a greater impact on the sport than most of us realize. Evidently a lot of the gray areas have been removed so it is more black and white and therefore thinner.
Bill Borden is a former championship winning crew chief who operated David Pearson's Racing School for many years.