Shock tuning can be a tricky business, since the process involves so many variables. To simplify and demystify, we delved into the forces at play, established several basic aims for whittling down lap times, to provide a clear direction for the ambitious amateur to follow.
To do this, we consulted with the wise Tim Anderson of QA1. His background in road racing, circle track, and autocross has made him a source of wisdom to help with the challenging task of trying to distill complex problems into simple, near-universal solutions. Regardless of the type of car, engine placement, or drivetrain layout, his suggestions should teach the technically competent and talented driver how weight is transferred, to where the weight should transfer depending on the car’s position in the corner, and how the car should ideally respond.
A Concise Introduction to Shock Tuning
It’s easy to get mired in the variables present, but before we begin worrying too much about damping, we should try to figure out if the entire tire is being used, and if the car has the proper alignment and suspension geometry. More specifically, it helps to set the proper camber and caster settings first, then try and diagnose the shock-related issues. This way, we can keep the confusion to a minimum.
With those out of the way, we can start with a fundamental understanding of the shock’s purposes and what it should ideally provide. The three main tasks shocks perform: to change ride quality, to absorb bumps, and to adjust the rate of weight transfer. The first two tasks are closely related, since they basically address the same issue but result in different outcomes, depending on the circumstances.
A marshmallow-soft suspension allows a vehicle to bounce after encountering a bump or depression in the track. If a shock is too stiff, hitting a bump can bounce the tire into the air, or at least unload it for a significant period of time. And as the old adage goes: “an airborne tire gathers no cornering force.”
On the other hand, excessive stiffness is unnerving, since it makes the car feel as if it’s skating over the uneven portions of the track. Since this might be hard to recognize depending on the circumstances, two telltale signs of overly stiff suspension are “wheel chatter and much more tire temperature on the outside,” Anderson advises.
Since ideal setups are always different from car to car, it’s hard to make many sweeping generalizations. What can be said, however, is that under-powered cars often benefit from a little more stiffness in the rear, as the aim is to get them to “free up” earlier; not bind the front end and slide into the right attitude come corner exit. Since wheelspin won’t compromise the exit too much, we don’t have to worry about getting the rear to dig in as well.
That changes when a V8 drives the rear wheels. “With more power, the rear needs more rebound,” says Anderson. This makes for greater compliance at the rear. “More rebound will provide more forward drive in suspension movement for a longer period of time to help get out of the corner,” he explains.
So much in solving a handling problem comes down to how quickly weight transfers heading into a corner. Whether a car understeers or oversteers depends largely on the rate of weight transfer. The happy medium is between too little body control and a “locked down” chassis that offers little compliance. The aim in the end is simple: keep the contact patch of all four tires squarely on the surface of the road at all times, while still retaining the necessary amount of stiffness to keep the car predictable and responsive.
The Differences Between Bump and Rebound
The shock has two basic movements. Compression — sometimes referred to as bump — which occurs when the shock shaft pushes the piston into the shock body. Rebound is the process of the shock shaft pulling the piston back and the shock returning to full extension. In other words. “Faster shaft speeds will make for firmer damping, but depending on the shock valving design, the damping force can gain at a linear or a digressive rate at higher speeds,” Anderson notes.
The reason for this is simple. Manufacturer’s adjustable shocks can be tuned for more than just compression and rebound. High-speed compression is a function designed to handle bumps and determines overall traction, whereas low-speed compression helps manage weight transfer smoothly and progressively by changing the handling balance of the car.
In general, compression determines how much weight is sent to a tire. Some telltale signs of compression being set too firmly include the initial reaction to a bump might be harsh, and/or the car might jack up in long corners due to the higher ride height. If there’s too little compression, the car has too much longitudinal weight transfer (squat and dive), and the inside-front tire and outside-rear could fall over.
Rebound, on the other hand, controls how quickly weight leaves the tire. Too much rebound can result in the wheels unable to keep up with changes of the road’s surface. If there’s too much rebound, the wheel can oscillate after a bump, thereby making it a chore to turn the power into propulsion.
Now that we have a basic understanding of the forces at work, let’s delve into how to get the most from your setup and how to address different handling issues.
Managing Corner Entry
When heading into a corner, braking first loads the front wheels, then adding steering input begins to load the outside tires. As a general rule, the outside-front and inside-rear are the most heavily loaded, and therefore have the greatest effect on cornering performance.
If the front begins to lose grip between the turn-in point and the apex, the driver can make two important changes. First: address the front suspension. “Soften the front compression,” Anderson suggests. Then, the rear axle can benefit from a corresponding change to help get the front end to work well. “To make the most of the change to the front, you should soften the rear rebound,” adds Anderson. These two changes allow for more weight transfer to the front end.
If the car begins to oversteer once the brakes are applied, the weight transfer needs to be better controlled; it needs to be slowed from rear to front. To do that, “The front compression needs to be increased, and the rear rebound does too,” he notes.
The mid-corner section is always tricky to diagnose accurately, since there are an abundance of variables at play. What’s important to know is that shock travel is at a minimum here, since the longitudinal forces are smallest and the lateral forces greatest. For this reason, the basic aim is to ensure the car remains flat throughout this phase, which lasts different amounts of time in different cars. Super stiff, lightweight, thoroughbred racing cars like prototypes and formula cars generally get through this phase quite quickly; the driver is able to transition off the brakes to the the throttle with little to no delay.
However, in a production-based race car, the mid-corner phase takes a few blinks. The reason it takes a little longer for a production-based car to move through the middle phase of a corner are the car’s higher center of gravity and greater weight. Therefore, to make sure the chassis remains flat throughout this phase, one will “want to know if there’s enough rebound to ensure a longer set,” Anderson advises.
If the car begins to oversteer strongly in the middle of the corner, it’s important to add more rebound to the inside front tire or decrease rebound from the outside tire. “This increases weight on both the outside-front and inside-rear,” he points out. Again, getting the weight distributed evenly across all four tires is the basic aim in this challenging, elongated mid-corner phase.
At corner exit, the opposite of the entry phase occurs. While the rear shocks go into compression under acceleration, the front end goes into rebound. In the case of a left-hand turn, these forces cause the left rear wheel and right front wheel to move the most, since they’re under forces working in the same direction. If the rear begins to slither post-apex, Anderson advises two changes: “Lighten up the rebound on the front-outside tire and soften the compression on the inside-rear.”
If the car begins to understeer at the exit, the car needs to pivot a little more. To get this, “Add rebound to the outside-front tire, and take some cross-weight out of the car. This keeps more weight on the inside-front and outside-rear, which ought to make it pointier.”
There is a basic series of steps to go through to limit the number of variables, simplify the diagnostic process, and isolate the root cause of the problem. First, once someone has worked through setting the proper alignment, caster, and camber settings, then they should focus on shock settings. However, if the car breaks away in the mid-corner phase, but not in their entry or exit phases, perhaps the problem is not in the shocks, but in the alignment.
If this hasn’t been done, shock changes will leave the driver scratching their head as they try to deal with a different suspension issue. If the handling issue isn’t remedied with shock adjustments, then it’s probably time to move onto the swaybar or springs. Word to the wise: move in small increments. Several clicks per change at most — and try to focus on one corner at a time.
However, before you adjust the shocks, you have to try and figure out what the issue is. Drivers with extra mental reserves to pay attention to their car’s handling always have a strong advantage over the rest of the field. However, the drivers who are stretched thin from pushing too hard can improve their diagnostic abilities by dialing back their effort a bit, since consistency is paramount. It pays to drive in a fashion that is repeatable for a series of laps. If you’re holding on for dear life just to try to post a fast lap, you’re not in a position to learn how your vehicle is responding to chassis tuning.
QA1 has developed a unique removable valve pack that can be interchanged in minutes — with the shocks still on the car — to provide a greater range of adjustability at the track without having to send them out to be re-valved.
A Second Set of Eyes
Even the most sensitive drivers can struggle to comprehend everything happening with the platform when navigating a corner at triple-digit speeds. For that reason, bringing in a spotter can help. “It helps to have a skilled set of eyes watching on the sidelines,” Anderson suggests.
Determining the exact point at which the issue begins can save you from plenty of frustration. For instance, problems at the beginning of the corner can sometimes transform at mid-corner and the exit, thereby complicating the diagnostic process. Lest we want to be misled, we need to determine where the root cause is located. We can help pinpoint the problem by asking, “Where exactly is the car breaking away?”
For example, let’s assume that excessive entry speed is the root problem — not the snap oversteer it becomes, come corner exit. Though the snap might seem to be a greater issue, it’s only a byproduct of a benign imbalance in corner entry. For this reason, “It is best to diagnose handling issues in this sequence: entry, mid-corner, then exit, as an early issue will present a later, misleading issue,” Anderson elaborates.
Once we graduate to a certain level of success in racing, we might not like to self-criticize the way we manipulate the inputs. But, retaining some humility is critical when assessing a handling fault, since technique and consistency are relevant factors in diagnosing a problem. You should also consider your familiarity with the car when struggling, since the lines and throttle applications that worked in an old Corvette might not lend themselves to a new BRZ. You must tailor your driving style slightly, though this is no excuse to avoid appropriate suspension adjustments. At the end of the day, you should drive in a way which complements the machinery, but also optimizes the car to suit the track itself.
Though every car and every suspension setup is different, these suggestions ought to send a competitive driver down a fruitful and interesting path. As the sharp end of the pack, even in club racing, is often separated by minor changes in setup, these tips can make the difference between Fourth and First. At the very least, they should help minimize the time spent cursing, scratching heads, and banging wrenches in the pits when there’s so much fun to be had on the track.