Don’t Roll With It

Antiroll Bar Tech: Where Bigger Isn’t Always Better

By Jeff Smith   –   Photography by the Author

Everybody wants a car that handles well. Any new car built in the last 30 years will far out-corner a stock ’60s machine with little trouble but it is also easy to upgrade and improve corner prowess with the bolt-on simplicity of an antiroll or sway bar. But once you dive into the nuances of suspension modifications, the answer isn’t always just to bolt on the biggest bar. It’s a bit more complicated than that. So let’s dive in.

001 QA1 sway suspension
The easiest way to improve handling on a near-stock Chevy from the ’60s or early ’70s is with an antiroll bar kit like this one from QA1.These bolt-on bars will create a marked improvement in cornering speeds and response to steering input.
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Factory cars from the ’60s were especially weak in suspension design with regard to improved handling. This is evidenced by soft spring rates, very tiny antiroll bars, and less-than-ideal alignment specs, which were all aimed at driver comfort rather than any attempt at better handling. But that means there are plenty of opportunities for a simple and effective upgrade with the addition of a front and/or rear antiroll bar. The approach for this story will be aimed at the average street enthusiast who just wants a slightly better handling machine.

002 determine antiroll bar diameter is to slip an open end wrench over the bar
The best way to measure a sway bar diameter is with a simple dial caliper. But if a caliper is not available, another quick way to determine antiroll bar diameter is to slip an open-end wrench over the bar. Larger bars will require a 1 1/8- or 1 ¼-inch open end wrench or you could substitute a large adjustable wrench and measure the opening. This bar is 1 3/8 inches in diameter.

We’ll focus our initial discussion on front antiroll bars and slide into rear bars. The idea behind an antiroll bar is to increase resistance to roll when the car is driven into a tight corner at an aggressive speed. The front suspension’s normal reaction in a lefthand turn is to compress the right front spring. Of course, you could minimize this roll with very high-rate springs, but that also affects ride quality, so another way to minimize body roll is with a torsion bar that connects to the frame and also to both lower control arms. As weight transfer attempts to pitch the body, the bar’s diameter and lever arm combination work to resist this body roll.

Check it out: Third-Gen Camaro Rear Suspension and Brakes and Rearend Upgrade

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It should also be emphasized that suspension tuning is very much a team sport, meaning that all the players at both ends of the front and rear suspension have an important part to play in this handling game. This means that while a stiffer antiroll bar will certainly improve the handling game, other components like spring rates, shock absorbers, control arms, chassis stiffeners, and other components are also essential components. And if you’re like us, that first improvement always seems to lead to diving further into the program in the search of even greater performance!

003 ideal handling for the front suspension at the center or the midpoint of this classic bell curve
One way to think of handling performance for a front antiroll bar would be to position ideal handling for the front suspension at the center or the midpoint of this classic bell curve. The far-left portion of the curve represents a bar that is severely undersized and does not apply sufficient load to prevent body roll. The far right of the curve would be a bar that is too large and applies too much load, which would severely limit suspension movement. The vertical scale for this example would be idealized handling. In both extremes the car will understeer in a hard cornering situation. The point here is that in every case there will be a happy medium between springs, shocks, and antiroll bar stiffness that will produce the optimal handling.

An antiroll bar is nothing more than a torsion bar configured to easily mount to the vehicle. A torsion bar operates by creating resistance to motion based on load input on one end against a fixed position on the opposite end. The bar’s diameter and length combine to create a resistance to being twisted. Length plays a part since a shorter bar of the same diameter offers a higher rate than a longer version. The rate is generally expressed in pounds of resistance per inch of travel. Most factory replacement antiroll bars are bent to establish a fixed lever arm on each end. The bar’s rate is directly affected by the length of the lever arm. It should make sense that a given diameter bar using a longer lever arm will deliver a lower rate compared to the same diameter bar with a shorter lever arm.

004 Tubular bars are generally as stiff or stiffer than their solid counterparts because the center portion of a solid bar contributes little to torsional resistance
As solid antiroll bars become larger, they also get heavy. Several companies now offer tubular antiroll bars that are often stiffer than their solid bar cousins. Tubular bars are generally as stiff or stiffer than their solid counterparts because the center portion of a solid bar contributes little to torsional resistance.

This becomes less of an issue with bolt-on antiroll bars because in most cases the lever arm length is fixed for the application, so the main variable is the bar’s diameter. The quickest way to evaluate a typical antiroll bar for a specific vehicle is to measure its cross-sectional diameter. A larger-diameter bar will always be stiffer than a smaller diameter for the same vehicle. Since the lever arm distance will remain the same for any given vehicle like an early Camaro, Chevelle, or ’55-57 Chevy, the main variable that remains is the bar diameter as a way to change the resistance value.

005 Scotts Hotrods N Customs front suspension
. This Scott’s Hotrods ’N Customs front suspension reveals the use of a straight front sway bar attached to the frame that is splined with long arms to the tubular lower control arm.

A slightly different approach to the front antiroll bar that is becoming increasingly popular are the splined sway bar kits. These bars employ a straight torsion bar located inside an outer housing. Both ends of the torsion bar are splined to lengths of steel or aluminum arms that attach (in the case of a front antiroll bar) to the front lower control arm. A similar arrangement can also be applied to the rear suspension. The advantage of the splined bar is that if at a later point a slightly stiffer or softer bar is required, it’s easy and sometimes less expensive to make the change. Or the lever arm can also be changed separately. Plus, for more advanced suspension tuners, these straight bars can be varied in wall thickness to effect minor changes in rate.

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More Suspension: Rebuilding a Chevelle’s Front Suspension with CPP

As an example, we looked at Speedway Engineering’s chart on typical hollow splined torsion bars 37½ inches in length. If the length of the lever arm is increased by 50 percent (from 6 to 9 inches, for example), this decreases the effective rate of the bar by 33 percent. We can also decrease the rate of our torsion bar by 33 percent by changing from a 1-inch to a 7/8-inch diameter. These percentages will change with both length and bar diameter, but this at least offers an idea of how these bars can be tuned to produce the rate required.

006 62 Impala with a combination of large diameter adjustable sway bars Global West springs and QA1 double adjustable shocks
How many ’62 Chevys have you seen on a road course? Dale Snoke has improved the handling on his ’62 Impala with a combination of large-diameter, adjustable sway bars, Global West springs, and QA1 double-adjustable shocks. This is a shot of the car at a recent event at Auto Club Speedway in Fontana, California. Photo by Mike Morgan.

In an accompanying chart, we’ve also listed a test performed by Hotchkis on the effect of changing from a solid to a hollow bar. The bar diameters in this test are not the same, but because there is relatively little torsional resistance offered near the center of a solid bar, a hollow bar with a given wall thickness can be stiffer than a solid bar. In the Hotchkis test, the hollow bar is 1/8-inch larger yet still delivers a 19 percent increase in stiffness despite being 9 pounds lighter.

Some people consider a front sway bar to be sprung weight because it is bolted to the frame. But since a portion of the bar is also attached to the lower control arm, a portion of the bar is assigned as unsprung weight. In all applications the ideal situation is to minimize the unsprung weight. In the case of a rear antiroll bar attached to the lower trailing arms on a Chevelle rear suspension the entire bar would then be considered unsprung weight.

007 control arms and big block springs from Global West
The front suspension on Snoke’s big car consists of control arms and big-block springs from Global West, and a large, splined front antiroll bar that was adapted to the ’62 with Speedway Engineering components. The car works very well combined with Global West suspension pieces out back.

Now that we’re on the topic of rear antiroll bars, it’s worth looking at rear antiroll bar mounting positions of various designs. GM often attached its antiroll bars directly to the lower control arms. While this is a convenient place to attach the bar, this location also reduces the bar’s effectiveness. This occurs because the functional lever arm length is not just the length of the attachment portion of the bar. Instead, the true lever length actually begins where the trailing arm is attached to the chassis. This drastically increases the length of the lever, which then reduces the resistance offered by the bar diameter. A more effective placement is to attach the lever arm directly to the frame of the car instead of to the lower control arms. Some aftermarket rear bars are constructed this way. While they require more installation effort, the return is certainly worth the time spent.

008 requires its own sway bar mounting position
Many companies, like Art Morrison Enterprises, emphasize a conversion to a completely redesigned front clip, which requires its own sway bar mounting position as in this version for ’67-69 Camaros. Note the front bar offers three different positions for the endlink, which allows tuning its effectiveness.

Armed now with this baseline of torsional twist tech, there are a number of factors that go into selecting the right antiroll bar. We have some experience with early Chevelles and much of this also applies to other Chevy muscle cars. A larger antiroll bar is a great first step in reducing body roll while not drastically hurting ride quality. Someone way back in the ’80s discovered that second-generation ’70-81 Camaro and Firebird antiroll bars were a direct retrofit to an early Chevelle, so adding a 1 1/8-inch Trans Am bar was a great step up from those wimpy stock 7/8-inch bars. Even with a larger front bar early Chevelles still tend to understeer, so adding a rear bar tends to stiffen the rear suspension and this helps reduce the tendency toward understeer.

009 typical connection between a front sway bar and the lower control arm
This is the typical connection between a front sway bar and the lower control arm using a long 5/16-inch bolt with washers, spacers, and polyurethane bushings instead of rubber.

However, other front suspension components to improve corner entry eventually get to the point where the rear is now too stiff and the car will want to oversteer. That’s when the rear bar should be removed to soften the rear suspension and allow the car to remain neutral on corner entry. But if we continue to stiffen the front suspension in our quest for higher corner entry speeds, the car will eventually begin to understeer because it’s too stiff. We’ve included a graph of a classic bell curve that might help explain this series of events, if you think of the horizontal axis of the graph from left to right representing increasing stiffness in the front suspension. A car can understeer as a result of too little front roll resistance or it can also understeer from excessive roll resistance. This is a very simplistic evaluation because the back half of the car also affects this situation, but at least this offers some clues to suspension dynamics.

010 suspension companies are now converting from the more common polyurethane endlinks to these aluminum spherical endlinks
Many aftermarket suspension companies are now converting from the more common polyurethane endlinks to these aluminum spherical endlinks that can make adjustment a little more precise.

So far we’ve only discussed antiroll bars for turning corners but they can also be used in drag racing. Street cars tend to have somewhat compliant chassis, especially if not improved with reinforcements or a rollcage. We’ve all seen cars leave the starting line with the rear tires firmly planted while the front half of the car is twisted like a pretzel. This occurs with a combination of excellent traction and sufficient torque to literally twist the car. Rear antiroll bars are designed to reduce this twist by employing a large rear bar bolted to the rear axle and to the frame of the car to limit this body movement.

011 bar is bolted to the lower control arms
In the factory rear antiroll bar configuration, the bar is bolted to the lower control arms. This makes for convenient bar placement but the lever arm is significantly longer since it originates at the front pivot point of the lower controls arms. This longer lever arm reduces the effectiveness of the bar.

This story has really just touched on the high points of this subject matter without getting into more exotic ideas, such as the blade type antiroll bars that are rate adjustable by making a small change in the angle of a blade-style connector. These types of bars have yet to make their name in the domestic street/autocross/road course market but are already found in race cars and upscale import vehicles. Expect to see more of these as the corner-turning set bumps up the technology curve; all in the name of negotiating corners a little bit quicker.

012 This rear antiroll bar attaches to the rear axle and the frame and is intended for drag racing to control front end twist
This rear antiroll bar attaches to the rear axle and the frame and is intended for drag racing to control front end twist, which it does quite effectively. The only drawback to this design is its weight using a solid bar and brackets that add roughly 40 pounds to the car’s unsprung weight.

This is a partial list of replacement antiroll bar diameters for ’64-67 Chevelles and ’70-81 Camaros. A stock front bar for an early Chevelle was generally 7/8 inch in diameter so a 1 3/8-inch bar is a radical increase in torsional stiffness.

Company Bar Dia. (inches) PN
Addco 1 1/8 883
Addco 1 ¼ 709
Addco 1 3/8 2278 Tubular
CPP 1 1/8 CPP883
CPP  CPP709
Heidts 1 1/8 SB071
Global West 1 1/8 SB-883
Global West DB-884
Hotchkis 1 3/8 2202F
QA1 52870
Ridetech 1 3/8 11239120

 

Hotchkis’ test of solid versus a tubular (hollow) sway bar. Note how the tubular bar, while larger yet 6 pounds lighter, also delivers a 19 percent increase in roll resistance rate.

Solid 1 ¼” Bar Tubular 1 3/8” Tubular Difference
Weight 22.5 lb 16.4 lb 6.1 lb lighter
Rate 477 lb/in 567 lb/in 90 lb/in stiffer

 

Sources
ADDCO
(800) 338-7015
addco.net
Art Morrison Enterprises
(253) 922-7188
artmorrison.com
Classic Performance Products
(866) 517-0430
classicperform.com
Global West Suspension
(909) 890-0759
globalwest.net
Heidts
(800) 841-8188
heidts.com
Hotchkis Performance
(877) 466-7655
hotchkisperformance.com
Performance Online
(888) 991-1697
performanceonline.com
QA1
(952) 985-5675
qa1.net
Ridetech
(812) 482-2932
ridetech.com
Roadster Shop
(847) 949-7637
roadstershop.com
Scott’s Hotrods ’N Customs
(800) 273-5195
scottshotrods.com
Speedway Engineering
(818) 362-5865
1speedway.com
Speedway Motors
(402) 474-4411
speedwaymotors.com

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