Big Sway Bar, Soft Springs Setups - BBSS

There is a setup trend that has taken hold in circle track racing over the past several years in which teams have been using much softer front spring rates and very large-diameter sway bars. Some teams have had a measure of success while others have become frustrated trying to make it all work for them. Before softening up your setup and sticking in a large sway bar, let's look at how the sway bar works, what influences the bar has on the setup, and where we can possibly utilize this combination.

When racers across the country were asked if lap records have fallen since teams have switched to the big bar/soft springs (BBSS) setups, the general consensus was that lap times are about the same as before for the fast cars. If that is true, then why bother?

In other conversations, racers tell me an inexperienced driver can generally do better with the BBSS setups than trying to figure out the more conventional setups. That being said, the majority of all setups suffer from an imbalance anyhow, and maybe the BBSS setups bring the car closer to a balanced state than ever before for some teams.

Jay Fogleman is a top Hooters ProCup driver who has a great deal of short-track experience in the Late Model divisions. Fogleman thinks that with the BBSS setups, along with the stiffer right-rear spring, the car already feels set on initial entry without having the driver wait for the car to take a set. This lets the driver get into the throttle sooner, whether that is an improvement or not. The bottom line is that, in some cases, it makes the driver feel more confident.

Since opinions vary, it gives us something to think about and play with. After all, racers were born to experiment, and for most circle track racers, the search for the ultimate setup is nearly as much fun as the results. Let's take a good look at what sway bars do, some general characteristics of sway bars, and how we can utilize the BBSS setups.

Definition
A sway bar is, in effect, a type of torsion bar designed to act as a mechanical resistance to body sway or roll. As the car rolls, the bar must twist, and the stiffness of the bar, or resistance to twisting, determines its effect. Most asphalt cars have sway bars in the front suspension and sometimes in the rear suspension. Using a sway bar means softer springs can be used without the negative effects of excess body roll.

One type of sway bar seen on a circle track car is the one-piece tubular or solid type that resembles the stock sway bars that come on factory passenger cars. On the Nextel Cup cars, and increasingly installed on Late Model Stock cars, are the straight bars with arms attached over splined ends of the sway bar.

Sway bars are rated by the pounds of resistance per inch of arm movement of each arm. A bar rated at 300 pounds per inch means that if the bar is secured and the end of the arm is moved 1 inch, we would measure 300 pounds of force or load if the end of the arm were resting on a spring rater.

A coil spring is merely a sway bar that is coiled. When we compress a coil spring, the resistance is created by the wire twisting exactly as it does in a sway bar. The amount of resistance is related to the diameter of the wire, the length of that portion of the wire that is allowed to twist, the length of the connecting arm, and the stiffness of the metal, usually referred to as the shear modulus.

The shear modulus (SM) is different for various types of metals. It is represented by a number multiplied by 10 to the sixth power to determine the pounds per square inch (psi) rating of the metal. The number for cold-rolled steel is 11.5. Heat-treated carbon steel is rated from 11 to 11.9, and stainless steel is rated at around 10.6. It is almost impossible to know for sure what the SM is for a particular bar, but, for our calculations, we can use an average number of 11.5, which would be an average of the various metals used.