SWAY BAR SWAGGER! HOTCHKIS IS LEADING THE WAY

Lead

HOTCHKIS PERFORMANCE: HANDLING AND HAULING!

Until recently, truck owners had very limited choices when it came to their suspension: leave it stock, and suffer through excessively sloppy handling and body roll reminiscent of a rowboat during high seas, slam the truck with drop springs and get a spine-jarring ride, or use an expensive airbag kit that provides a perfect stance but can be costly and difficult to install. One easy way to improve handling and overall drivability is to control body roll and improve traction with aftermarket sway bars, or as they’re sometimes known anti-roll bars.

 

A pretty standard performance Sway Bar kit – tubular front and rear non-adjustable bars. Note that the front bar is larger in diameter than the rear, allowing for neutral handling (a larger rear bar would create serious oversteer).
A pretty standard performance Sway Bar kit – tubular front and rear non-adjustable bars. Note that the front bar is larger in diameter than the rear, allowing for neutral handling (a larger rear bar would create serious oversteer)
02

Here’s a real-world example of body roll. The huge gap between the top of the tire and the fender lip, along with the frame being at an extreme angle compared to the ground, mean the center of gravity of the truck is shifting, creating a smaller tire contact patch.

 

 

Nearly every truck produced in the last 75 years came equipped with at least one sway bar from the factory, but OEM cost cutting and ride quality considerations meant most trucks rolled off the showroom floor with very small diameter bars that kept suspension geometry in check but didn’t do much to control body roll or handling. Luckily, aftermarket sway bar technology has improved dramatically in the last decade with hollow tube technology leading the way.  Gone are the days sway bars were produced from extremely heavy solid bar stock.  Now superior CNC bending equipment and precise engineering allow for lighter weight tubular sway bars possessing the twist resistance of solid bars with a fraction of the weight. Lighter weight more efficient sway bar packages are standard equipment on new vehicles ranging from new Silverado pickups to Corvette ZR1s and a Porsche Turbos.

They key to understanding sway bars in the classic truck market is that well-engineered sport sway bars that are made in the USA by a reputable company will provide more bang-for-your-buck handling improvement and overall fun factor than nearly anything else you can do to your truck, and most kits can be installed with hand tools in a few hours.

03

This truck with performance sway bars has minimal body roll going into a corner. There’s minimal fender gaps, and the control arms and body are parallel to the ground

 

 

HANDLING DEFINED

Most trucks new and old, come  from the factory with significant understeer as a safety precaution. Understeer, also called “push,” is what happens when you enter a turn at a high rate of speed and front tires howl while the car continues to move forward in a straight line. Essentially the rear tires are overpowering the front tires and the vehicle goes straight.

 

 

04

Figure 1 shows no body roll, and maximum tire contact patch. Figure 2 shows that as the vehicle corners and the body rolls, the left spring compresses, the right spring extends, and the tire contact patch changes shape. At the end of the corner the spring loads will make the truck rocket back the other direction, unbalancing the vehicle and degrading handling.

 

     “Oversteer” is when the front tires stick and the vehicles turns into the corner while the rear tires lose traction and the rear of the vehicle tries to rotate around the perimeter of the turn. While dangerous for a novice driver, an experienced hot shoe can control this with the throttle for more aggressive driving.

Sway bars can provide adjustment of driving dynamics like understeer and oversteer by transferring weight to different corners of the suspension as the vehicle navigates a corner. In many cases adding a rear sway bar when there isn’t one from the factory, or adding a stiffer rear sway bar, can make a system designed to understeer either neutral or oversteer.

 

05

This line drawing explains how the sway bar works. By tying the frame to the control arms, the bar forces the frame to stay closer to parallel with the ground and maintains a more consistent tire contact patch. The sway bar is really a big spring, it provides enough give that the ride stays compliant.

 

Body roll is a reference to the load transfer of a vehicle towards the outside of a turn. When a vehicle is fitted with a suspension package, it works to keep the tires in contact with the road, providing grip for the driver of vehicle to control its direction. This suspension is compliant to some degree, allowing the vehicle body, which sits upon the suspension, to lean in the direction of the perceived centrifugal force acting upon the car. Sway bars are a part of the suspension specifically designed to address body roll.

 

Body roll of the vehicle (body and chassis) relative to the ground is not necessarily bad. Most performance suspension setups try to keep the frame of the vehicle as parallel to the ground as possible to maximize tire contact patch (aka handling). However completely eliminating body roll can also create a very stiff ride, so finding a balance that keeps the suspension geometry working correctly and the body parallel to the ground (thereby controlling the vehicle’s center of gravity) while also maintaining a comfortable ride is the key.

 

“Why should I change my Anti-Roll Bars from the stock ones?” Well it’s pretty simple. Enthusiasts typically demand more from their cars than the average driver. They need improved handling, increased high-speed stability and better traction. Properly designed and tested Anti- Roll bars give a car, truck or SUV optimum handling potential and chassis balance. This is accomplished during testing by changing the roll couple (changing the stiffness of the front vs. rear Anti-Roll Bars) to achieve the optimum handling balance. Generally, neutral to slight understeer, but it depends on the application and vehicle. Auto manufacturers are out to give the average person the car that will suit most of their needs. If they install larger anti-roll bars, stiffer springs and lower the car, they will create more customers that are dissatisfied with their car than if they offer a ‘detuned’ car. They opt to cut cost, and raise customer satisfaction ratings by offering a decent, if not mediocre, car. This leaves considerable room for increases in the suspension’s performance or ‘tuning’ using aftermarket parts.

 

06

Modern performance sway bars are design in programs like Solidworks or CAD, starting with factory mounting points and then determining shape, tube diameter and roll stiffness

 

07

In most cases, bars need to articulate independently while still tying the axle or control arms to the frame. This is where greasable bushings and endlinks come into play

Sway bars explained

Basically sway bars reduce roll and dramatically improve handling.  They connect one side of the suspension to the other with attachment points generally on the lower a-arms and frame (chassis), and twist to limit the roll during cornering.  As the truck enters a corner centrifugal forces create a body roll force.  This force is limited by the twisting actions of the sway bar.  The stiffer the sway bar the more resistance is extended to counteract the body roll.  Too much sway bar stiffness creates excess pressure on the outside loaded tire causing a loss of traction.  Sway bar stiffness is calculated by the force required to twist one end versus the other and calculated in lbs/in.

 

08

Here we see (L to R) raw bar stock, a factory small diameter bar and a performance aftermarket bar. Note the smooth radius bends of the aftermarket bar, which improve strength

 

Sway bars work off of torsional force (twisting motion). Therefore, the material in the center of a solid bar plays little role in the resistance of torsional force. With this in mind, hollow bars eliminate some of the center material and move it to the outside of the tube, where it is most effective. In turn, this produces a sway bar that is lighter in weight and just as stiff, if not stiffer than solid. For example, a 1’3/8″ hollow bar is equivalent to a 1’1/4″ solid. But the 1’3/8″ hollow bar is 6% stiffer and 43% lighter than the 1’1/4″ solid.

 

09

This aftermarket bar (L) is adjustable, with three mounting options for different torsional stiffness settings, vs the stock bar (R). The further in the endlink is mounted to the center of the bar, the stiffer it will be

 

 

Years ago most trucks were only equipped with a front sway bar. Back then the best tires were skinny with relatively soft sidewalls. Today people are running modern super sticky tires. These tires produce serious grip and are miles better than yesterday’s race tires.  Your truck will be the quickest and most comfortable around a corner or on your favorite twisty road with a neutral handling balance. This is achieved when the car is neither loose nor tight (excessive understeer or oversteer) but balanced with the front and rear tires doing equal work. Providing that the springs are of sufficient rate to keep the car from bottoming out, the handling balance is tuned with the front and rear sway bars. When talking to suspension designs at Hotchkis Performance, they said they typically engineer the largest front sway bar possible that doesn’t overpower the front suspension and then tune (change roll stiffness) with an adjustable rear sway bar.

Some people recommend running a stiff rear spring combination without a rear sway bar. In this case the heavy spring rate keeps the chassis from rolling thereby eliminating the need for a rear sway bar. This is fine if the passengers wear kidney belts and interior rattles are no problem – but most truck owners know that a stiff rear spring and an unloaded bed can be brutal on long hauls. For the rest of us we want a comfortable ride with great handling. Adding a rear sway bar solves the ride quality issue and creates an optimum handling balance. The rear spring rate can be softer for better ride quality and corner exit traction because the rear sway bar (not the springs) is controlling the rear body roll.

Now that we know sway bar roll stiffness minimizes body roll, to make the truck handle well and remain balanced during cornering the front and rear sway bars must be tuned to work together.  Well-designed sway packages offer balanced handling and are adjustable to fine tune handling characteristics to the driver’s preference.  The adjustment is accomplished with holes in the sway bar end that allows the end link to be positioned in multiple locations effectively lengthening (softening) or shortening (stiffening) the sway bars.  Due to the end link mounting location and reduced benefits of an adjustable front sway bar, companies like Hotchkis Performance often design the adjustable rear sway bar to be between a two and four hole difference.  The adjustment holes give the driver a great tuning advantage because each hole is at least 100 lb/in difference.

 

How Sway Bars are Made

 

10

The best modern sway bars are created by bending high-quality domestic steel bar stock in CNC controlled benders, eliminating swedges and tooling marks

 

Manufacturing a sway bar has been done by various methods throughout the years. The traditional method of making a bar is to take the raw bar stock, and bend it into the shape you want by using a press and bend dies. This is generally a cheap way to make them, and there are several drawbacks to this method. The first such detriment is that each bend is done separately. With each bend the tolerance increases, i.e. inaccuracy, in making the part. This allows for increased human error in production. As trucks become more complex, the packaging of the sway bar tightens. There is less room for error, and thus, the part needs to be more accurate to fit in the car. Another disadvantage is that the press bends can add several extreme tooling dents or ‘marks’ to the product. Dents such as these are acceptable on a solid bar, but they make the part less eye pleasing to look at. Tubular material cannot be bent in this traditional way. The press will either kink or crack the tubing when bending the material.

 

11

Companies like Hotchkis Performance then use Laser Vector scanners to check bars from every run during quality control to ensure maximum accuracy

 

A set of freshly bent bars are waiting to be finished. Some companies weld cast ends to hollow bars, but a stronger method is to heat and forge the ends from the same tubular bar stock

 

Companies like Hotchkis use a CNC (Computer Numerically Controlled) bending machines and tubular stock. The CNC does all of the bends in one handling process. Raw material is loaded into the machine, which then goes through a series of motions to produce a smoothly bent part. A computer keeps track of each bend in relation to all of the other bends. This produces a very high tolerance part, typically in the 0.050” range or tighter, and with consistent reliability. During the manufacturing run, a Laser Vector inspection system is employed to measure the parts being bent by the machine. This measures the shape of the bar, and compares it to a computer file of the part print. The laser’s computer sends any necessary corrections directly to the bending computer. This is done because each batch of raw material varies and bends slightly different than another.

 

13

14

This is Hotchkis’ Sport Sway Bar kit for the Chevy C10 pickup. Note the unusual rear sway bar design, which is a “blade type,” similar to what’s employed on NASCAR racers

13

15

The blade type bar offers adjustability like a traditional sway bar, but provides more articulation and better packaging options in truck-arm equipped vehicles like the C10

16


Endlinks are what attach the sway bar to the suspension. In many cases, factory endlinks (top) are very weak and not designed for the loads found in performance setups. Aftermarket endlinks (bottom) like this Hotchkis unit use heavy duty hardware and high-performance heim joints

17

Standard sway bar bushing brackets are usually “strap” style brackets made from pressing a piece of flat steel. Hotchkis recently released these billet brackets that offer more strength and adjustability thanks to slotted oval holes

 

 

 

1313

Testing

Like all aftermarket products, sway bar testing procedures can vary from company to company. Some of the lower end products are simply upsized versions of factory parts with increased rates and are not tested at all. The more high-end components like those manufactured by Hotchkis are rigorously tested at the track and on the street for the optimal balance of handling improvement, driver feedback, adjustability and ride compliance. John Hotchkis states that his company tests uses 200’ skid pad, 600’ slalom, road course and street drive tests to ensure every system works correctly.

 

18

Standard sway bar bushing brackets are usually “strap” style brackets made from pressing a piece of flat steel. Hotchkis recently released these billet brackets that offer more strength and adjustability thanks to slotted oval holes.
02- After sway bar installation, it’s often a good idea to align the truck with a performance alignment

 

In conclusion, a well-designed, lighter weight tubular sway bar package is the best handling benefit you can bolt on to your classic truck. The next step in the bolt-on handling equation is a set of premium shocks.  These will make a world of difference and improve overall suspension performance and ride quality.

19

Once your new sport sway bars are installed, you’ll notice reduced body roll, neutral handling and incredible grip

You must be logged in to post a comment Login

Leave a Reply