This car is set up from recommendations that were published by some dirt Late Model builders about seven years ago. Since that time, most manufacturers of dirt Late Model cars have changed their view of a starting setup. Many now publish starting front spring rates that have lower overall rates and a LF spring that is stiffer than the RF spring. This reverse split helps the car on turn entry.
The older base setup makes the car so tight that the driver would need to throw the car sideways in order to have any chance at all of setting up a good line for coming off the corner. We can make the following changes to help the car turn better and make it more neutral in the middle of the turns so we don't have to be nearly as sideways.
1. Soften and reverse split the front spring rates to: LF = 375, RF = 350 for dry-slick only2. Reduce the rear spring split to: LR = 200, RR = 1753. Change the J-bar to 12.0 on the left and 9.5 on the right.4. Move the dynamic MC 2.5 inches to the left of the centerline5. For tacky/tight track conditions, we would raise the rear MC even up the rear springs, and level out the J-bar
The plan for setting up all dirt cars is to narrow the gap between roll angles, front and rear, but not necessarily match them exactly like we do on asphalt cars. This method provides enough front grip so that the car will turn well, but still allows adequate rear bite so that the car has enough rear grip to get off the corners.
On tracks where there is plenty of moisture and the grip level is high, we can set up the dirt Late Model more like an asphalt car with even spring rates in the front and rear and a higher average J-bar. This is not theory, but reality, as some major dirt races have been won with even spring rates front and rear.
This car has a front MC that is too far to the right of the centerline for a flat asphalt track. It also has stiff front springs and too much rear spring split. The roll angle difference is 1.3 degrees, and that makes for a very unbalanced and inconsistent setup. This car might be fast for a few laps, but in the long run, the lap times will fall off quite a bit.
These changes will balance the car while still providing sufficient bite off those flat corners. A high crossweight percent range works best to help with exit performance.
1. Change the front spring rates to LF=350, RF=3252. Change the LR spring to 185. The split is reduced to 10 pounds,versus the original 25 pounds.3. Raise the Panhard bar to: 10.75/11.754. Move the dynamic MC width to the left to end up 2.0 inches to the right of the centerline.5. Use a high crossweight range (a range more equal to the left-side weight percentage)
The reverse spring split on the front helps the car on entry to the corners. If we were to run a stiffer RF spring than the LF, the car would begin to roll to the left when braking into the corners because of the softer LF spring. As the car continues to drive further into the turn, the front must reverse and roll to the right. This gives the driver a very uncomfortable feeling and can best be described as a "flip-flop" sensation.
When we use a stiffer LF spring, the car will begin to roll in the same direction as we brake into the corner that we would normally see at mid-turn. The transition is smooth, and the driver will have more confidence on entry.
The rear spring split with the softer RR spring helps promote traction in the rear by increasing the crossweight percentage as load is transferred to the rear upon acceleration. Usually, a 10- or 15-pound rate split is sufficient to provide the desired effect, whereas a split of 25 or more is often too much.
The front MC change (moving the MC to the left) makes the front suspension feel softer and more efficient and makes it want to roll to a greater roll angle to match the rear suspension's desired roll angle.
For the big bar and soft spring setups at flat tracks, we would change the springs to look something like this: We reduce the front spring rates, increase the size of the sway bar, and increase the right-rear spring rate (but not too much). The original setup has a right-rear spring that is much too stiff. This is not necessary and may unbalance the car, with the front out-rolling the rear.
There are special shocks that are built in conjunction with these BBSS setups, and we recommend that you consult your shock manufacturer so that the setup matches the shocks. Be careful when trying to run soft front springs at high-banked tracks. The car may bottom out and cause damage.