SMOOTH THINGS OVER WITH SUSPENSION OPTIONS
Improving the performance of a late model vehicle is not confined to what is under the hood. Vehicle performance involves the entire vehicle. It’s more than just going faster in a straight line; it’s catching speed around a curve and stopping at shorter distances. That requires performance suspension parts, including upgraded bushings, shocks, struts, springs and brakes.
The functions of the suspension of any vehicle are to (1) track the vehicle in the steered direction, (2) absorb irregularities in the road surface, (3) provide a comfortable ride for the vehicle’s passengers, and (4) stop the vehicle safely.
A standard vehicle is designed to understeer a bit to help ensure that the driver does not lose control of the vehicle. Understeering can be thought of as having to turn the steering wheel more as the car moves through the turn. This is accomplished primarily by using a stronger front suspension setup than in the rear and more weight bias toward the front of the vehicle.
Oversteer can be thought of as having to turn the steering wheel less. If a vehicle is designed to oversteer a bit and the driver puts more steering wheel input during a turn than needed, the rear of the vehicle can break loose and the driver can lose control.
Oversteer can be viewed as a built-in safety feature that is very desirable for the general public and normal street driving. An understeering vehicle has a tendency to slow down going through a turn since speed is scrubbed off, making it more difficult to lose control.
But if someone wants to go quicker through turns, less understeer is desirable. An oversteering vehicle has a tendency to go quicker through a turn since less speed is scrubbed off, but the risk of losing control increases.
Enhancing the performance of a suspension is all about modifying the components to shift the handling characteristics from understeer to oversteer. In the real world of production cars that are sold as street performance vehicles, the goal is for the suspension to be neutral. When the vehicle goes through a turn, the steering wheel is turned in the direction of the curve and no additional input is needed. The car goes where it is steered.
In order to shift the suspension characteristics from the production-designed understeer to a more neutral inclination (and, even a bit of oversteer), the chassis needs to be stiffened and the weight bias shifted toward the rear of the vehicle. There are some tradeoffs with ride quality, but nothing that feels as rough as driving a truck.
If you look underneath a car when it’s on a rack, you can see all the attachment points for the control arms, shock absorbers and suspension links. Each one of these connection points uses a bushing to isolate the component from the mounting bracket so there is no direct metal-to-metal contact. Without bushings, the ride would be rougher.
When a vehicle goes over a bump or goes through a turn, all of the suspension components move. Unfortunately, the connection points move, too, because the bushings distort a little bit. While this movement may not seem significant, it affects the performance of your suspension. The first step in improving suspension performance is stiffening it, which is done with harder bushings. These harder bushings do not twist as much as standard bushings, keeping the connection points located properly.
And, in conjunction with bushing upgrades, the anti-sway bars are also replaced with larger diameter pieces (Figure 1).
The anti-sway bar is basically a large spring that twists as the vehicle goes through a turn. The twisting motion pulls the opposite side of the vehicle down to keep the vehicle from leaning too much to one side. If a larger diameter bar is used, it is more difficult to twist. The net result is the vehicle travels flatter through a turn. When a larger diameter bar is used on the rear suspension, the vehicle characteristics change from understeer to neutral. Also, the bushings are upgraded to better secure the anti-sway bar. A DIYer can install upgraded anti-sway bars and bushings on the front and rear of a vehicle in an afternoon.
Changing the springs and the struts/shocks is another common practice in upgrading the suspension. If you watch a NASCAR race, you might see a mechanic adjusting the right rear coil spring — either compressing or extending it. When the spring is being compressed, there is more force on that corner, increasing the amount of oversteer (this is also known as making the car looser). While adjustable coil springs are not practical or economical, upgrading to stiffer springs can accomplish the same goal (Figure 2).
Strut and shock replacement is another popular option. In the same vein as upgrading the coil springs, upgraded struts and shock absorbers help stiffen the vehicle with the aim of developing neutral steering characteristics.
Finally, stiffening the suspension can be greatly enhanced with the installation of a strut tower brace (Figure 3). As mentioned, a suspension is improved when the component mounting locations are stiffened, usually with upgraded bushings. A strut tower brace will aid in keeping the upper strut mounting locations in place. This is especially true if engine upgrades have significantly increased torque and horsepower.
We can’t discuss performance suspension modifications without talking about the brakes. We all know that bigger is better. In other words, larger rotors and pads will provide more braking power than smaller rotors. But, if you want to increase the braking power on your production car, like a late model Dodge Dart, larger diameter rotors are not always necessary.
Mopar® offers high-performance street brake rotors with directional slots machined into the rotor surfaces and high performance brake pads for the front and rear brakes (Figure 4). The pads provide improved braking and the slots help dissipate heat, decreasing the likelihood of rotor warp.