The Ups And Downs Of Sprint Car Torsion Bars With Sway-A-Way

Sway-A-Way’s torsion bars are powder coated to guard against surface contamination, plus they look great.

Every dirt track racer’s goal is to optimize “bite” and stay at the head of the pack. As such, suspension adjustments play an important role in week-to-week success. And for sure, torsion bars are at the heart of the matter. The torsion bar is part of a Sprint Car’s suspension, which twists in response to the up-and-down motion of the wheels, absorbing their vertical movement.

The pre-stressed bars are clearly identified as to where they go on the car. This is absolutely essential.

For some insights into this key, but often taken-for-granted part of a race car, we turned to Brian Skipper, Mechanical Engineer and president of Sway-A-Way Inc., a highly respected suspension components manufacturer who has been making torsion bars for more than 30 years.

Sway-A-Way President Brian Skipper is shown with one of his company’s popular pre-set torsion bars.

The Golden Rule Of Torsion Bars

“The most important thing to remember is that torsion bars should never be twisted in the opposite direction after they’ve been run,” said Skipper. “A sprint car or dirt modified torsion bar should always be run on the corner it was designed for, although it can be run on the opposite corner in a ‘X’ pattern on a sprint car,”  Skipper added. “Flipping the bar does not change the corner it can be used on. You can flip it end-for-end on the same corner or cross it.” Sway-A-Way pre set Torsion Bars are clearly labeled from the factory “left front/right rear” or “right front/left rear” to keep them organized.

Torsion bars are pre-stressed to predetermined levels to provide racers with predictable, long-term service.

The #83 car owned by Roth motorsports, was driven by Daryn Pittman when they won several races en route to the WoO Championship. The car was equipped with Sway-A-Way torsion bars.

Determining Spring Rate

The actual spring rate is determined by the length and diameter of the bar, with the arm length also a factor in relative wheel rates. Of course, there are both solid and tubular-style torsion bars on the market, so the size of the bore (typically .750-inch), and the outside diameter must be taken into consideration. Most manufacturers of tubular bars, increase the diameter in the middle of the bar so that it has the same spring rate as a solid bar. The only advantage to a tubular bar is weight savings, typically about 60-percent the weight of a solid bar of the same rate. Tubular or gun-drilled bars do not “respond quicker” as some rumors in the market would suggest.

Before and after hobbing. Note the groove machined into the end to secure the torsion bar arm.

Generally speaking, Sprint Cars are a bit more sensitive to spring rates than Dirt Modifieds, so Sway-A-Way’s Sprint Car torsion bars are 30-inches long and come in rates of 1000, 1015, 1025, 1050, and 1060 on the high end, and 900 to 975 increments on the low end. Dirt Modified bars are typically 29-inches long and have incremental increases in diameter of .025-inch from .900 to 1.050. 

Remember, a tubular bar will have a larger outside diameter than the same rate solid bar so it has the same rate as the solid bar. A 975 spring rate tubular bar will measure larger in diameter than the same rate solid bar which will measures .975-inch. Sway-A-Way machines a circlip groove in each end of the bar for a simple, inexpensive, and effective arm-retention feature required by many race promoters. 

Splines are machined through the tried-and-true hobbing process.

Pre-Stressing Torsion Bars

As a function of physics and metallurgy, torsion bars will “take a set” over time, affecting the performance of the bar. They will not have the same spring rate forever. Accordingly, the life expectancy of a torsion bar can vary. However, to optimize performance, Sway-A-Way pre-sets its torsion bars in a special computer-controlled device that essentially twists it to a predetermined setting. This greatly increases the life of the bar, and eliminates the typical settling that is seen with bars that are not pre-set.

Here’s the finished “business end” of the torsion bar with splines and the retainer groove.

Tiner Hirst Enterprise’s #94 has also found success with Sway-A-Way torsion bars.

The Optimum Setup

There’s obviously art and science involved in “reading” a track and being able to set up a car to take advantage of prevailing conditions. All the power in the world won’t help unless it can be efficiently put to the ground.

Having an arsenal of arms and torsion bars of various spring rates will greatly help in tuning the car. Most Sprinters rely on torsion bar arms between 14 and 18-inches in length.

The torsion bar is about to be inserted into the collet, where it will be rotated to a predetermined angle.

Proper Maintenance Helps

Successful racers will remove the torsion bars after each race, leaving the torsion stop on to aid in re-assembly. Clean the grease off the bar and inside of the bushing. Reapply a coating of quality lubricant to the bar and bushing.

A machinist puts each Sway-A-Way torsion bar through its paces. Pre-setting has many important benefits.

Life Expectancy

While some racers may advocate that a torsion bar is only good for about 20 races, Sway-A-Way’s skipper says, “The life of a bar is determined by many factors and a set number of races is very arbitrary. Pre-setting a torsion bar definitely increases the life, eliminates the re-setting of a new bar after it has been run, and provides a more consistent spring rate throughout its life.

Article Sources

About the author

Bill Holland

Bill Holland has been involved in racing and the performance aftermarket since the 1960s in the capacities of racer, speed shop proprietor, journalist, street rodder, designer and advertising/PR/marketing professional. Along the way he’s raced Top Fuel and Funny Car, been editor of NHRA’s publication, National Dragster, was involved in off-roading as publisher of SCORE News, built a variety of Featured Vehicles for the SEMA Show, as well as a Track “T” that was a Contender for the AMBR award. He currently races vintage sports cars. Bill was inducted into NHRA’s California Hot Rod Reunion Hall of Fame in 2017.
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