Story and Photography by Richard Newton
When you drive around a corner the inside wheels want to lift off the pavement. The faster you go around the corner the greater the lift. This means you don’t have all of the tire on the pavement. The faster you corner the less rubber you have on the ground. We need to find a way to push that inside tire back into the ground.
The easiest way is to use a torsion bar (or spring) that runs from one side of the car to other. Corvettes normally have two of the torsion bars. We just call them sway bars or anti roll bars. Since 1984 Corvettes have always had one sway bar in the front and another sway bar in the rear. The rear sway bar was optional in the earlier generations.
What a Sway Bar Does: As the inside tire tries to come off the ground this spring, or torsion bar, pushes the tire back into the surface of the road. This spring is often called an anti-roll bar. Some people call it a sway bar. I like the term anti-roll bars since it’s much more descriptive. The purpose is to decrease body roll in a corner. No matter what you call this thing it works the same way.
The Corvette was one of the first cars to use sway bars and in fact Zora Duntov introduced the idea to Porsche engineering back when he was a Porsche factory driver. Actually Zora got the idea from the Roll Royce company in America. The first sway bar patent was awarded to the Canadian S. L. C. Coleman of Fredericton, New Brunswick on April 22, 1919.
There are two ways to increase the effect of your sway bar. First you can change the diameter of the bar. As the diameter of the bar increases it takes more force to twist the bar. If you use a smaller diameter sway bar it will have the opposite effect.
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| When you change the length of the arm you're increasing or decreasing the amount of leverage. |
Another way to change the force of the sway bar is to increase (or decrease) the length of the arm. This is all about the arm of the sway bar acting as a lever. A bigger lever will have a totally different effect than a short lever.
Remember that the purpose of the the sway bar is to push the inside tire into the ground with more force. There are times when that’s a good thing. There are also times when that’s a bad thing. You want different sway bar strength for different tracks.
GM changed the diameter of the bar for various C4 applications. The length of the arm was never changed. They tuned the handling package of the C4 Corvette by changing the spring rates and sway bar diameter.
With the C4 Corvette you have five different solid sway bars for the front and four different diameters for the rear. If you start swapping them around you end up with twenty possible combinations. That’s just counting the solid sway bars. The largest diameter sway bars were used on the R9G and Corvette Challenge cars.
Trying to determine which of the twenty combinations will be best is almost impossible to determine. GM spent millions of dollars and thousands of hours seeking the best sway bar combination for a given application. You probably can't make a huge improvement in your home garage.
Trying to determine which of the twenty combinations will be best is almost impossible to determine. GM spent millions of dollars and thousands of hours seeking the best sway bar combination for a given application. You probably can't make a huge improvement in your home garage.
Rear Sway Bar Choices: (All Solid)
19-millimeter
20-millimeter
22-millimeter
24-millimeter
26-millimeter
The 26-millimeter rear sway bar is almost impossible to locate. It was used on the Corvette Challenge cars. The 24 mm bar isn’t easy to find but it can be located. If you want serious handling that’s the bar to look for.
Front Sway Bar Choices: (All Solid)
24-millimeter
25-millimeter
26-millimeter
30-millimeter
I like to keep things simple. I just put the biggest diameter anti-roll bars on my car that I could find. That means I have the 30mm bar on the front of the car and the 24mm bar on the rear. I do want some adjustability though. I don’t want to keep swapping different sway bars around at the track. were very close to what was used on the race cars. They're also a lot easier to locate.
I like to keep things simple. I just put the biggest diameter anti-roll bars on my car that I could find. That means I have the 30mm bar on the front of the car and the 24mm bar on the rear. I do want some adjustability though. I don’t want to keep swapping different sway bars around at the track. were very close to what was used on the race cars. They're also a lot easier to locate.
The one thing that has always been lacking on the C4 is an adjustable sway bar. Actually it hasn’t been lacking – it’s just been a well-kept secret. Danny Kellermeyer, who owns D.J. Racing, has been using an adjustable sway bar for years. Now we all can have an adjustable sway bar.
Danny welds an extension on each side of the rear sway bar arm. He then drills three holes into this new extension. The middle hole is the same as the stock setting. You now have an option of making the bar stiffer or softer.
Adjustability is wonderful if you have a lot of time and knowledge. I have neither. That means I want a limited number of adjustments. The D.J. Racing sway bar gives me three different settings to play with. That's more than enough.
Softer and Stiffer: When people use the term softer they mean that the sway bar has less effect. The softer setting on an adjustable anti-roll bar means that you’re trying to minimize the effect of the bar. A stiffer setting means that the anti-roll bar will have more of an effect on your car’s body roll.
The Adjustments: The idea here is very simple. If we change the length of the arms on the sway bar we change the way it reacts. Think back to high school physics and levers. A longer lever allows you to lift more. In other words a longer lever twists the sway bar more.
Forward Hole - Softest Setting
Middle Hole - Original Factory Location
Rear Hole - Stiffest Setting
Forward Hole - Softest Setting
Middle Hole - Original Factory Location
Rear Hole - Stiffest Setting
The Links: These are what connect the ends of the sway bar to the suspension. The C5 and C6 guys all buy expensive aftermarket links with heim joints. As C4 owners we don’t have any choice. Stock links are just fine. They work. I was prepared to spend hundreds of dollars on special links and heim joints for my sway bars. Then Danny explained that during all the years he raced the C4 Corvette he used the stock end links.
Tubular vs. Solid: The main difference between solid and tubular anti-roll bars is the weight. There’s also a difference in the stiffness in the two types of bar. If you think about it for a minute you’ll see that a solid sway bar requires twisting the entire solid bar. With a hollow bar only the walls of the tube twist.
A common misconception is that a solid bar is stiffer than a hollow one. This is only partially correct. If a solid bar and a hollow one of the same diameter are compared then the solid bar is stiffer than the hollow version. If you increase the outer diameter of the hollow bar and fine-tuning the wall thickness you can get the same performance that you might get with a solid sway bar while reducing the weight of the bar.
The additional complications and downsides of hollow bars though seem to outweigh their advantage in overall weight and unsprung mass. The advantage of a hollw sway bar seem to only be marginal in actual applications. Large manufacturers rarely use a hollow design in their sway bars. However with the right conditions and setups there are some gains. This is especially true in racing situations which can require weight reductions as small as a few ounces.
With the C4 Corvette a partial switch was made to tubular sway bar on the front in 1986. A tubular bar was also used on the FE1 package. GM though stayed with the solid 30mm bar on the Z51 package. When the RG9 cars were developed GM used the solid 30mm front anti-roll bar. This was also the case with the Corvette Challenge cars.