Anti Sway Bars

Do you yearn to turn?

Driving a stock vehicle highlights the fact that its design was a compromise between the average driver’s capabilities, the average road surface, the average turn; do you see a trend? Let’s see a show of hands, how many want to drive a car rated “C” in overall handling? When we buy a car it is now up to us to improve handling performance to somewhere way above average, to match our expectations and abilities. The anti-roll or sway bar is a very reasonable way to vastly improve how the car feels. Upgrading your ride will loose its nasty habits like understeer or body roll or both.

Understeer is a condition where the car seems to “plough” or “push” through the corner. Believe it or not this is done by design. The auto manufacturers look at the skills of the “average” driver and set the car up to understeer, that’s right, to understeer! This is because they assume that you are incompetent at handling your vehicle up to and beyond the limit of traction. The conventional wisdom goes something like this: If the car understeers and pushes around a corner the rear end will still have traction so the pointy headed little driver will not get in trouble swapping ends; spinning out. In the corporate world of paranoia concerning lawsuits makes total sense.

Race cars or autocross cars are set up to be neutral steer or slight oversteer. Neutral steer is self explanatory, neither over nor under steer. Oversteer is where the front end stays planted, with plenty of traction but the rear tires tend to loose traction first and the car has a tendency to swing the tail end out in a hard corner. Obviously you have much better directional control with neutral steer or slight oversteer because the front tires have traction. They are not sliding like an understeer setup.

With a neutral or oversteer car now the driver is responsible for keeping the car headed through the turn in the track, road, or course. It is then possible to control up to the limits of traction and negotiate the turn as fast as possible under the prevailing conditions, and your skill. Isn’t that better than to accept a compromised vehicle that an engineer and corporate lawyer decided was good enough for you?
“But my car has a sway bar.” That may be true, most modern factory cars have cute little paper clip sway bar that add spring rate, just not enough, and many have no rear sway bar. While bigger is better is good up to a point, most factory suspensions are whimped out to meet the lawsuit requirements of corporate management.

Here are some guidelines for achieving improved results:

Understeer: Increase rear sway bar diameter or decrease front sway bar diameter to restore balance.
Oversteer: Install either a smaller rear bar or a larger front bar.
Match Bars with Springs

Selecting a sway bar should be done in conjunction with your springs. I you are planning to upgrade to stiff springs, then you probably wont need to increase the sway bar diameter since the added spring rate will handle body roll. A larger diameter bar is required if you have softer springs. Many people prefer a softer ride, but want to limit body roll and opt for softer springs. Here are some helpful generalities:

Stiff springs, small sway bars.
Soft springs, large sway bars.
With all generalities there are tradeoffs. The stiff spring / small bar arrangement is generally better for overall handling because it reduces front to back weight transfer. This is because the spring rate is higher and helps resist the tendency for a car to “dive” in breaking, or “squat” during acceleration. Both conditions will upset the vehicle by changing suspension geometry and can make handling worse.

Rock & Roll Control

Driving a car that is a “leaner” is no fun. You wonder if the door handles are going to scrape off negotiating a tight corner. Even if your car has stiff suspension a properly sized anti-roll or sway bar will improve its stance in a corner. That is because the bar adds spring rate as the vehicle tries to roll. On the straight away or when not maneuvering the spring rate is not there. To add the additional spring rate needed to stay relatively flat in a corner would mean a really stiff, uncomfortable ride.

How is it possible to just selectively add spring rate? The diagram shows the ingeniousness of a sway bar in that it is a torsion spring which is tied to the suspension and body through the sway bars bushing and the vehicles moveable suspension parts like the lower a-arm in front or the differential housing (non-independent cars) in the rear. The net result is that it is affective only when the vehicle tries to lean. Consider it spring on demand. The more the vehicle tries to lean the more it resists leaning. On the other hand when you go over a bump that is across the entire road the bar rotates in its bushing with no addition of spring rate. This directional bias makes it perfect for reducing body roll.

swayBar2

Click Image to Enlarge

 

Body roll is also connected to whether a car has bad habits like oversteer previously discussed. That’s because the more the body rolls the more is messes with the steering geometry (mostly camber) causing the car to do things you would not expect when you corner. We have shown the front suspension but the rear can use the same treatment only with a much smaller bar diameter since front engine vehicles have so much more mass to affect the front suspension.

How Much is Too Much?

With this knowledge you would think you would want to bolt on the biggest, baddest sway bar you could find. Not a good idea, you see the suspension needs to be able to react to the irregular surface of the road or track in a straightaway and in a corner. If you put a huge sway bar on when you start to corner the spring rate (stiffness) of the suspension will go way up disproportionately to the weight of the vehicle. The suspension becomes so rigid that it can not do its job of properly following the surface to keep the maximum contact patch (tire footprint) against the surface. You will loose traction, reduce the maximum speed you can take the corner, and it will ride just like a go-kart when you hit a bump in a corner – like it had no suspension at all – ouch! From this you can see that properly sizing the sway bar is essential if you expect to improve the handling, reduce body roll and retain the ride characteristics.

Solutions

If you are a Corvette C2 or C3 owner SpeedDirect has a tailored package that matches springs, shocks and sway bars for an optimal combination depending on three driving preferences:

Shark Bite TM Cruiser TM Suspension Stage Kit – A smooth ride that handles great.
Shark Bite TM Instigator TM Suspension Stage Kit – Firmer ride, improved handling.
Shark Bite TM Nemesis TM Suspension Stage Kit – Solid ride, maximum handling.
One of these is right for your driving preference and style.