How To Tune Your Suspension To Maximize Lightweight Car Performance: 3 Important Tips
The job of any performance car's suspension system is really quite simple: maximize the amount of contact that the tires can make with the asphalt below. Those four small strips of rubber at each corner are the only part of a vehicle that actually touches the track, and everything about chassis setup is designed to ensure that they are used as effectively as possible in a high speed driving environment.
Although marketing departments have spent untold millions of dollars convincing enthusiasts that stiffer = better when it comes to suspension systems, the reality is a little more complicated. This is especially true when considering lightweight cars, which are more prone to nervous, jittery handling if their chassis settings are so stiff that the entire vehicle begins to bounce up and down. Once that happens, you're reducing the tire's contact patch and very quickly taking yourself out of the running in any type of competitive driving.
What tuning tips work best with lightweight cars? We've put together a primer on how to get the most out of your suspension setup without giving in to the stiffness monster.
Where's The Weight?
When tuning a vehicle's suspension, it's necessary to know not just how much it weighs overall, but also how that weight is distributed. The static balance from front-to-rear will help you understand your vehicle's handling and braking characteristics at speed, but don't neglect side-to-side balance as well. A car that isn't properly corner-balanced can put undue stress on individual brakes, tires, and shock absorbers, asking them to do more work than their compatriots and reduce handling and stopping power.
When balancing, you can actually 'move' weight diagonally across a vehicle to achieve the handling characteristics you are looking for. How does corner-balancing (also known as 'corner-weighting') work? The goal is to get to a 50/50 balance across the diagonal from the front tire to the rear tire on each side, which is called the 'cross-weight.' Adjusting cross-weight is accomplished by moving the spring perch on a set of adjustable coilovers to either raise or lower the vehicle's ride height on a given corner, which changes the amount of load being supported by that tire. Lowering the ride height reduces the weight on that corner, as well as the corner diagonally opposite to it, and raising it will boost it up.
In order to properly corner-balance your vehicle, you'll need a set of scales, one under each wheel, as well as a full tank of fuel and either yourself sitting in the driver's seat, or a representative amount of ballast. Most scales will do the cross-weight percentage calculation for you, and on a road course you're aiming for 50 percent diagonally. Remember to make small, incremental changes to get to where you're going, as opposed to big swings in ride height that may be more difficult to work with.
Too Much Sway Bar?
Too much stiffness isn't just an issue with shock absorbers. Larger-diameter swaybars can also reduce chassis flex to the point where wheels leave the ground while cornering, which is a particular danger in small, lightweight cars.
Wheel lift reduces control and destabilizes a vehicle. The easiest way to avoid introducing this hazard to your suspension setup is to avoid installing a larger sway bar than you absolutely have to. This type of problem is frequently encountered when a driver is trying to balance out a sway bar at the front or rear of a vehicle by matching it with an even stiffer unit on the opposite end. It's always better to back down on sway bar stiffness rather than escalate it in terms of finding the right solution.
While you can tune an adjustable damper's rebound and compression settings, once a set of springs are on your vehicle you are locked in to their particular compression resistance, otherwise known as 'rate.' Thanks to the previously-mentioned marketing efforts, the idea of stiffer springs being better springs has long been accepted as dogma by track-day beginners. As with all suspension components, however, spring rates need to be chosen to mesh with the rest of the chassis setup, the vehicle weight, and the type of track that is being driven.
We're most concerned with weight in this article, which means understanding how spring rates affect how a car drives. Springs set your vehicle's height from the ground and protect the undercarriage from bottoming on over uneven terrain or when transitioning through elevation changes.
A heavier car requires a higher spring rate in order to keep it on the level under the high loads one would see at speed, but on a lightweight car, using too high of a spring rate can have a disastrous effect on trying to put power down after transitioning through a corner, steer properly, or keep the tires gripping when moving over rough pavement. This is due to the excess resistance to vertical and lateral loading found in a very stiff spring. A lightweight car simply does not provide enough force to compress the spring, which cannot absorb what the track beneath its wheels is sending its way. The result is a wheel that bounces up from, rather than sticks to, the asphalt.
Your vehicle's suspension is a system, with each individual component working hand-in-hand with the other towards the ultimate goal of providing as much control as possible on a race track.
Making changes in one area is going to have effects in another, which is why it's always a good idea to plan for incremental, or gradual updates to your suspension tune. This is especially true for lightweight cars, where small changes can have larger effects than they would when there's more mass at play. Being able to balance your vehicle's overall mass, power output, tire compound, and suspension response is key to putting together a car that fits you like a glove, rather than one that fights you through every corner.
Want to drive deeper into suspension setup? This guide will get you started on the most important concepts.