A Performance Suspension Guide
Suspension doesn’t get as much attention as it should in my opinion. Typically the conversation includes what brand lowering springs are getting installed, what size sway bar, and what brand of shocks with too little attention to how it all works together. So let’s take some time to cover the various aspects of suspension and how you can better select the parts you need to get your setup just right!
Springs support the weight of the car and are generally specified in pounds of force required to deflect (compress) the spring 1 inch, also known as spring rate.
What is spring rate?https://www.qa1.net/tech-center/spring-rate-tech
Spring rate refers to the amount of weight that is needed to compress a spring one inch. If the rate of the spring is linear, its rate is not affected by the load that is put on the spring. For example, say you have a 200 lb. per inch spring – it will compress 1” when a 200 lb. load is placed onto the spring. If another 200 lbs. is put onto the spring, the spring will compress another inch. At this point the load on the spring is 400 lbs. The rate of the spring, however, remains constant at 200 lbs. per inch.
The higher the number the firmer/stiffer the spring. Springs that take a linear amount of force to deflect are called linear springs while progressivesprings take less force to deflect initially and take more force to continue deflection as the spring is compressed. Progressive springs are popular with performance enthusiasts as they provide a more comfortable initial spring rate with a firmer final spring rate that keeps the vehicle more stable. A good way to think about springs is to remember that they limit how far the suspension moves, not how fast.
Whether you call it a shock, strut, or a damper the purpose of shocks is to slow down the vehicle suspension movement to absorb energy over time and make the ride more comfortable while also preventing the spring from ‘bouncing’ the wheel and tire off the ground after a bump or impact. Shocks dampen this energy both on the upward stroke (compression) and the downward stroke (rebound). Adjustable shocks that you find typically in the aftermarket will have rebound adjustment and higher end units will also have compression adjustment as well. The more stiff/firm the shock the shorter period of time it will dampen the suspension energy and the rougher the ride. A good way to think about shocks is to remember that they limit how fast the suspension moves.
A big mistake a lot of folks can make is thinking that the firmer the shock/spring combination the better. This is certainly not true as a setup that is too firm does not give enough feedback to the average driver to allow for them to feel and experience the edge of traction without going over it unaware. A car that is too ‘tight’ creates a fine line of traction that once crossed can be dangerous.
Sway bars limit the roll of the car by distributing the vehicle weight from left to right as well as the balance from front to rear. As with springs and shocks too stiff can be a problem and it’s important to remember that stiffer springs will affect the roll couple distribution as well so they become additive to effect of a sway bar. Most sway bars also can be ‘tuned’ to provide more oversteer or understeer by changing the mounting location on the end of each moment arm. Most manufacturers design quite a bit of understeer to keep the vehicle from ‘fish tailing’ which would likely scare the average driver and render the car as being branded unsafe. Understeer occurs when the wheels are turned but the vehicle does not follow the direction the wheels are pointing. Oversteer is the opposite, where the wheels are pointing in a direction but the rear of the car has lost traction and is not following the path of the front wheels. D1 drift drivers use oversteer to create excessive entry angles into corners to create entertaining driving.
Polyurethane suspension bushings are a popular upgrade and provide enhanced suspension dynamics by reducing the reaction time of the suspension when compared to driver inputs from the steering wheel. These type of bushings transfer the suspension energy more quickly which results in a more nimble vehicle and crisper steering and chassis feedback. For most newer cars the isolation of the chassis to the suspension is so well designed that when firmer bushings are installed the impact to driver comfort with regard to noise, vibration, and harshness is minimal.
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