The BBSS setups are easily recognized by the low and level front end while going through t
Big Bar and Soft Spring (BBSS) setups are the rage in asphalt racing circles right now. This setup uses a large sway bar combined with soft front springs and a very stiff right-rear (RR) spring. The problem is that you cannot just bolt those parts onto your car and go racing and expect to be successful.
We have talked to teams and component manufacturers about the transition, and we have run those setups in back-to-back tests against conventional setups. In short, we have a lot of information to share.
The very first thing to know is that the BBSS setups are not good for all racetracks. There are some tracks where the gains are significant, others where there is no gain at all, and some where the conventional setups are just plain faster. We'll explain why.
Goals Let's take a look at what our goals might be in going the BBSS route. Most ill-handling cars are traditionally tight and do not turn well. The BBSS setups help the car turn better by forcing additional load onto the left-front (LF) tire.
Handling balance can be accomplished with adjustments to the weight distribution, meaning a change in crossweight. So making the car neutral is not a problem.
Prepare your car in the shop before you go to the track. Use your old setup first and reco
Aero efficiency is improved, sometimes greatly improved on longer tracks, due to the front valence being lower and the rear spoiler being higher. The soft front springs compress more and the stiff RR spring forces the LF corner down to make the front of the car low and parallel to the track in the turns.
Results of the Setup There are some interesting results that come from the transition. First of all, if the car is set up "right," meaning all the way to BBSS (we'll explain what that means later), the dynamic balance is way off. The front wants to roll to 1-1.5 degrees, and the rear wants to achieve a negative roll angle from 0.5 to 1.0 degree.
This difference in desires indicates that a lot of extra load is being put on the RR tire. In older, traditional setups that were unbalanced, the rear outrolled the front and a lot of extra load ended up on the RF tire. That tire soon began to overheat and lose grip. The car either pushed badly or the driver overcame the tight condition with extra steering input until the car went to a tight-loose condition.
The final result was either a worn out RF tire or a burned out RR tire. One of the two was sure to go. So, why doesn't the RR tire give up in the same manner as the RF tire that was overloaded with an unbalanced conventional setup? We're glad you asked.
Many teams opt to install the NASCAR-style sway bar mounts instead of the one-piece mount.
We pondered the very same question and finally came to a conclusion. When the car is unbalanced, with the rear outrolling the front, the RF tire has to carry extra load, do extra work to keep the car on the track through the turns, and turn the car. This extra duty overloads the tire and causes it to give up.
With the BBSS imbalance syndrome, the RR tire does not have to turn the car. It only needs to keep the rear of the car on the track, and it carries a heavier load to help it.
Since the setup is unbalanced, with the front tires more equally loaded side to side than the rear tires, the front develops more grip. So we see the need to increase the crossweight to tighten up the car. That is exactly what we found when we did a back-to-back test at Florence (South Carolina) Speedway in the ASA Late Model Series South division.
BBSS Components Keeping in mind that there are many variations of the BBSS setups, let's take a look at a common configuration for the straight-rail Late Model cars that usually run a touring series. We will offer general directions, so don't run out and put this in your car. Every car is a little different, and a slow approach to the transition will keep you from getting into trouble.
When running a large-diameter sway bar, always try to use steel arms.
The sway bar sizes range from 1.375-inch diameter heavy wall thickness, to 1.50 inches, to 2.0 inches and more. For most Late Model cars, 1.50 to 1.75 is common. Some teams think the 1.375-inch bar is large, but it is not when going with the BBSS setup.
Front spring rates vary, from a pair of 150-pound springs up to 225- and 250-pound springs. Again, springs in the 200-pound range are too stiff. The RR spring is usually increased over conventional rates by 100 to 300 pounds. This means you would run a minimum of 250 pounds all the way up to and beyond 400 pounds.
The crossweight must be increased along with these changes. Typical increases are from 2 to 4 percent of total weight. It is often better to begin with the lower crossweight range normally used with stiffer springs and smaller sway bars (for a car with a front-to-rear percentage distribution of 50/50, it is around 51.5 percent cross with a conventional setup) and then add 3 percent or so until the car is neutral in handling.
Since the rear roll angle is a lot less than the front, we also want to lower the Panhard/J-bar about as low as it will go. With most chassis designs, we are limited to going down to 8-9 inches off the ground.
The RR shock will travel about half as much with the BBSS stiff spring in the car, so adjust your trailing arm angle to avoid rear steer to the right in the turns. With a normal travel of 3.5 to 4 inches, we usually use around 1.5-2 degrees of trailing arm angle in the right trailing arm. With the BBSS spring in the RR, reduce that to half, or 0.75 to 1 degree of angle-front high, of course.