The BBSS setups are finding...
The BBSS setups are finding their way into late-model trucks. Long a choice of straight rail late-model asphalt cars, the process is one that takes some attention to detail to get right. We’ll discuss how it should work.
Most of us are aware of the newer setups being run in both asphalt and dirt racing these days. Many of us are experimenting with trying variations of softer front springs combined with either coil-bind or running on bump rubbers for both types of racing. Interest is high as to how to accomplish those setups correctly.
What is happening on a large scale is that racers are guessing on spring rates, shock settings, and so on and getting way off on the balance of the cars and the performance suffers. But, we do know that some racers are getting it right and making it work.
So, we had a little discussion with Jason Enders, one of the founders of RE Suspensions in Mooresville, North Carolina. It supplies shocks, springs, and other components to almost all stock car racing classes and works with road racing teams too. RE's level of knowledge is up there as to staying on top of current trends and making them work on the track.
We divided this discussion into two segments, first asphalt racing and then dirt racing. Each is different in the goals and approaches we use. There are some similarities, but the information is best divided. Most of the information you will read here is a result of explanations Jason provided. The plus in all of this is that I totally agree with the information provided, as do many professionals who are winning races with this knowledge.
This is a graph of travel...
This is a graph of travel distance verses spring rate for a brand of bump rubbers. This is typical of most standard rubbers where the rate starts to gain slowly and then ramp up to very high rates. Each line represents a different hardness of rubber. With these graphs, you can predict your shock travel and then choose a rubber whose rate increase will match the shock travel.
The discussion centers on the use of bump rubbers. It's generally understood and accepted that coil-bind reduces the suspension to a solid state whereby the tires provide the only "spring rate." This isn't acceptable to the author or Jason and not the most efficient way to set up a race car.
For the purpose of this section we'll refer to asphalt setups used for the straight-rail cars. There are some differences between this class and other asphalt racing classes, but those differences are mostly spring rates and the resulting shock design to go along with those rates.
The BBSS setups require that we run on either coil-bind or bumpstops on one or both front corners of the car. Please choose bumpstops or rubbers. When deciding on which corner to do this, we need to think out the process. The whole intent of the BBSS setups is to attain a low and more level profile of the front of the car. Most racers interpret this to mean getting the left front down to make the front more level and parallel to the track.
That is a good goal, but can be taken too far. If taken to extremes, the balance of the setup can be disturbed and the car won't handle or be fast. Most successful application of BBSS setups incorporate getting the left front down.
There is a term that has been around since the late '90s and originated in Cup racing in setups for Daytona and Talladega. It's "tie-down" shocks. Many of us professional engineers reacted harshly to that term insisting that you can't tie down any corner of the car since we can't bolt the tire to the track.
In this illustration, the...
In this illustration, the bump rubbers are much softer where there is a higher amount of compression of the rubber possible until the rate goes up. Then, after a certain compression amount the rate goes up very quickly and stays somewhat more consistent.
So, I will still use the term tie-down, but the meaning will be related to higher rebound settings in the shocks, which will produce a slow rebound movement to restrict rebound of the suspension to hold the spring in compression longer. There is a logical reason why we need to do this that will be explained.
Getting the car down on bumpstops at the left front is, in actuality, causing a change in spring rate. You might be running a 150-lb/in spring in that corner and mechanical downforce causes movement that takes the shock down onto a bump rubber that has a rate of 1,000 lb/in to 1,500 lb/in.
The trick is to match the movement or ride of the shock so that you will be operating in that range and not higher. If you move too hard onto the bump rubber, the rate could well increase to upwards of 2,500 lb/in on to infinity.
This is just the mistake most racers make. By running a right rear spring rate that is too high, you force more load onto the left front suspension and cause the bump rubber to compress to very high levels of spring rate.
Jason states, "Too many racers are overly concerned with how the car looks." The front end doesn't have to be perfectly level to the track and the valance doesn't have to scrape the asphalt in order for everything to work correctly.