Big Bar and Soft Spring setups are the big ticket in asphalt racing. This setup uses a large combined with soft front springs and a very stiff right-rear spring.
Do Not Bolt or add bigger Sway Bars and softer springs without understanding how it all works. Below is fundamentals of this very complicated setup, this article is designed to help understand this type of setup and its not good for all race tracks, do your home work, try testing and go through all the motions before using this setup type.
The first thing for your knowledge base is again that the BBSS setups are not good for all racetracks. Some race tracks show significant gains in speed and handling and others are only showing better handling and speed by conventional setups using heavier springs and softer sway bars, Depending upon your situation, trying out a BBSS setup may waste valuable track time, and may not get you fast results if this combination is not right.
Use this guide, if the race track has more than 16 degrees banking, do not use this set up, if the track has large transition areas from the straights to the corners, do not use this set up. If the track is overly rough you may not want to use this set up.
The biggest goal of the BBSS setup is for more weight transfer to the Left Front tire, this helps with a tight situation or an overly loose condition. The handling balance is controlled by making adjustments to the weight distribution of the car, making a change in cross weight which makes the car more neutral.
By using the BBSS set up the dynamic roll is off from the tradition roll factors. The front wants to roll to 1-1.5 degrees, and the rear achieves a negative roll angle from 0.5 to 1.0 degree.
This difference in setups are that a lot of extra load is being put on the RR tire. In traditional setups that were unbalanced, the rear would out roll the front and an excess load would end up on the RF tire. That tire would gradually over heat and build up pressure. The car would develop a push and the driver would have to overcome a tight condition, then with excessive steering input, the driver would fight a loose-tight condition, making driving difficult.
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.
As a result of the unbalanced actions the RF tire would be worn out, and the right rear tire would burn up due to the rear out rolling the front, the RF tire had to carry the extra load from the cross weight change as the car goes around the corner, and as a result wears out and cant take the abuse.
With the BBSS imbalance syndrome, the RR tire doesn’t turn the car. It only keeps the rear of the car on the track, and because the rear roll is reduced it carries a heavier load to keep the rear from getting loose.
Since the setup is unbalanced, the front tires are more equally loaded side to side than the rear tires, with this the front develops more grip. Adding cross weight is needed to add more grip to keep the car from getting to loose.
BBSS setups require different components for different chassis, do not just go out and start bolting just any old part onto your chassis.
Sway bar sizes range from 1.375-inch diameter with a heavy wall thickness, to 2.75 inches. For most Late Model asphalt race cars, 1.50 to 1.75 is commonly used. Do not think that the larger bar is not for you, Using the BBSS setup means your going to be using the larger sway bars, so don’t think that something larger than the norm is not for you.
Front spring rates will vary by track, normally from a pair of 150-pound springs up to 225lb and 250lb springs. springs in the 200lb range are too stiff for the BBSS setup. The RR spring for the BBSS is usually increased over conventional rates by 100-300 pounds. A minimum of 250lb to a maximum of 400lb spring would be used.
The cross weight must also be increased when the springs are increased. Typically you will have to increase the cross weight by 2-4 percent of the cars total weight when using the BBSS setup.
It is often better to begin with the lower cross weight range normally used with stiffer springs and smaller sway bars used in conventional setups, which are on a neutral car 50/50 or about 50.1 percent cross weight, and then add 3 percent cross weight until the car is neutral in handling.
Since the rear roll angle is a lot less than the front due to the heavier right rear spring you will have to lower the Panhard bar or J-Bar down about as low as it will go. Most chassis designs 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 set up, adjust your trailing arm angle to avoid rear steer to the right in the turns. The normal travel of 3.5 to 4 inches in movement is seen using traditional setups, using the BBSS setup your going to see half that so the 1.5-2 degrees of trailing arm angle in the right trailing arm will be cut in half, now reduced to 0.75 to 1 degree of angle, which on the chassis will be front higher than rear of trailing arm.
Shock changes will be one of the biggest changes when using the BBSS setup, more compression is needed at the right front, while the left front sees less compression forces.
The RR might need more rebound to control the stiffer spring. Adjustable shocks are very helpful in the tuning stages of the BBSS setup.
The amount of rebound and compression will vary with the track size. A flat , long smooth track can use much more rebound control than shorter rough track. Rough tracks also have a negative effect on the RR when a very stiff spring is used. The car will tend to bounce as it goes through the corner instead of taking the bumps smoothly. It will be necessary to reduce the RR spring rate and decrease the cross weight to make the car neutral.
The cars aero Factor is increased by lowering the nose and raising the rear spoiler area of the car which increases down force, this is an added bonus of using the BBSS setup.
The front geometry must be redesigned in order to properly use the BBSS setup. Moment center location is still important, and camber changes are totally different.
Using the BBSS setup the Car Dives more but rolls less. The front end loses Camber as much as 3 to 4 inches in most cases, and low roll angles that normally would counter camber loss are not present.
The upper control arm angles need to be reduced. If you had 18 to 24 degrees of upper control arm angle with your conventional setup, you need to reduce it to 12 to 16 degrees while maintaining usable moment center location.
The static cambers themselves must be altered with the transition. The RF must be reduced from the normal (-) 3.5 to (-) 4.0 degrees to under (-) 2 degrees in most cases. These number are driven by the type tire used.
The LF tire camber must be increased from a normal 2.5-3.0 degrees to 4.0 degrees and more. It will lose about 3.25-3.75 degrees of camber in the turns.
Ackerman Steering is not a factor in using the BBSS, the LF tire is forced down during turns, which defeats Ackerman steering.
Do not use the BBSS set up if your race track has more than 16 degrees of banking
Do not use the BBSS set up if your race track has a large banked transition from the straight aways into the corner.
Make sure the RF suspension is not completely collapsed when in the turns, use a tattle tale device like the one Warren Motorsports Makes to ensure that you still have suspension left, if you bottom it out in the turn you will find the wall.
If you decide to use the BBSS Set up, make the car neutral in handling and run 10-20 laps, log down your information, speed, times, handling, feel. Then change the suspension back to the conventional setup and do the same, compare notes and see if the BBSS set up is for you.
If you decide to use the BBSS setup, make all the changes listed above. Use very soft front springs, install a large sway bar, raise the RR spring rate by at least 200 pounds, and adjust your shocks to the changes, and go racing.
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