Written by Andy Hollis
From the Nov. 2009 issue
The top of every race result or lap chart is typically dominated by talented drivers. But the pointy end of the field also has something else going for it: better equipment.
Sometimes that advantage comes from spending more money, but often it simply means optimizing the car and working the rules to the driver’s advantage.
A smart person once said that the last 20 percent of any job takes up 80 percent of the time spent on the entire project, and this surely applies to setting up a car for maximum performance. There’s a certain black art to extracting that last bit of performance that makes the difference between being in the hunt and landing on the podium—assuming the driving skills are present, of course.
Optimizing a car requires a metric for performance as well as a context for those measurements. For racing, the first part is simple: faster times. But the latter is a moving target, as the situation is ever changing. The venues, the weather and the other drivers on the grid constantly alter the situation. While you can’t control all of the variables, at least you can be ready for them.
So how do you get there? To start, you need to understand your working constraints and their level of priority: rules, budget and the like. From there, determine the strengths and weaknesses of your target vehicle and establish which variables will deliver the greatest overall performance increase. From there, you must optimize the parts—both individually and as part of an entire system—and learn to adjust for different situations. Sounds easy, right?
Before you start, you need to assess what you’re working with. This involves two basic steps: on-course testing and in-garage analysis. For the first part, put the car through its paces on an easy-to-drive autocross course or track session. During these runs, any weak points should immediately make themselves obvious.
Even better data can be obtained by breaking down the performance through the use of a skidpad, slalom and oval. The skidpad reveals the car’s basic steady-state performance, which impacts all other handling traits. Running up and down the slalom can tell you whether the car is nervous or composed, tail-happy or tight, prone to carving or skating.
Finally, the oval can be used to examine the dynamic effects of acceleration and braking. Does the car put down power properly coming off the corner? Do all four brakes contribute equally on corner entry or does one wheel have a tendency to lock up? How does the suspension react to the fore-aft weight transfer from acceleration and braking?
This is also a good time to verify suspension travel. Measure it by snugging a zip-tie around each shock absorber shaft where it meets the tube and seeing where it ends up, or by applying modeling clay between the suspension’s interference points.
Next, bring the car inside for a closer look at the shiny bits. Take measurements of the ride heights at each corner, the static position on the shock absorber shafts, and the alignment settings and range of adjustment. Also look at the corner weights at each wheel.
Now, remove the springs so the suspension can be moved through its full range of motion, taking note of the first point of contact for bumpstops or metal-to-metal impacts. This is also a good time to check for slop, bind or worn-out parts.
Looking at data acquisition can also help greatly. Is a buddy’s similar car consistently quicker off the line than yours? Does it accelerate better? Can it pull higher g loads in the sweepers or get through a slalom in less time? You may trail by a second or more per lap, but it could all be due to one single deficiency. Analyzing the entire car will hopefully unearth that problem.
Finally, a trip to the dyno for some baselines will tell you a lot about your engine—and your shocks. Shock absorbers? Sure. If you haven’t put your dampers on a shock dyno, you have no idea what you’re doing when you adjust them. Very few shock absorbers have linear adjustment ranges, and multiple examples of the same model don’t produce identical damping curves. Adjusting shocks without a dyno plot is like checking tire pressures by kicking the sidewalls.
Develop a Plan
Now that you know what you’re working with, you can develop a prioritized plan. If any low-hanging fruit showed up in the evaluation phase, start there.
If there are no obvious deficiencies, then follow the vehicle’s basic strengths and weaknesses. For example, a car with a low power-to-weight ratio will obviously benefit from more power and less weight, while high-powered cars should start with handling improvements.
Strangely, our experience has shown that the opposite typically happens: Drivers with lightweight, great-handling cars tend to give up on improving forward motivation, while those with big power always want more.
Making It Stick
Optimal handling starts with the tires. If you have a choice of brands and sizes, only testing will provide the best answer for your situation. Research via magazines and tire retailers is a great start, especially if you lack the means for testing. However, the best data comes from experimenting using your own car.
As part of the tire testing process, determine the optimal camber and pressures on a skidpad. Use a timer for final results, not just a pyrometer. Remember, quick times win races, not consistent tire temps.
Now you need to look at how the car’s body moves about. The job of the suspension is to maximize the tires’ efficiency. Those campaigning production-based cars face an additional challenge: dealing with the compromises made at the factory. In general, you want to reduce weight transfer as much as possible by lowering the car, but not at the expense of proper ride height or correct suspension geometry.
Stiffer springs can be used to keep those problems at bay, but they can also cause the tires to lose grip on bumpier surfaces. You’ll also need to valve the shock absorbers to properly match the springs—hopefully with some adjustment ranges to allow for additional tuning later. And remember, theory is great, but testing is critical. Always check your work both in the garage and on the track.
Use anti-roll bars to keep body roll in check by minimizing dynamic camber changes. Back at the skidpad, address any basic steady-state balance issues with the anti-roll bars. A general rule of thumb is to tune a rear-drive car to a slight steady-state push, while front- and all-wheel-drive cars should be as neutral as possible given their typically horrid weight distribution. Move to the oval to fine-tune the suspension and see how fore-aft weight transfer alters things.
Once the basic handling is established, move to the slalom to work on the transitional behavior. Sampling the shock absorbers across their entire adjustment range should reveal big differences regarding handling and speed. Once you know how the car behaves at the extreme ends of your damper adjustment ranges, you can hone in on the best compromise.
Toe settings will also have an effect on transitional performance, with front toe-out usually yielding better turn-in response and rear toe-in adding stability. Too much front toe will ruin the mid-corner balance, though, as will too much rear toe.
Finally, take the car back to the oval to see how power and braking impact handling. For example, rear-wheel-drive cars with big power will typically gain straight-line traction from more rear toe-in and less negative camber, even at the expense of some handling. Remember, it’s all a compromise.
One attribute that helps every aspect of performance is lightness, and that is why we are so obsessive about it. The lighter the car, the better it will accelerate, brake and turn. About the only downside is taking too much weight off the rear of a high-powered, rear-drive car, as wheelspin can become an issue.
Every part on the car offers an opportunity for additional lightness, and the rule book can become a guide, even in the more restrictive classes. Are cold-air intakes allowed? In addition to the power gains, look at the weight savings. Do the rules allow an aftermarket exhaust? Can the replacement save some weight, too?
Off-the-shelf parts aren’t always designed with weight savings in mind, so you may have to custom fabricate things to achieve your goals. Aluminum is your friend, while plastic is lighter than both metal and rubber.
Don’t skimp on safety, though, as something too light and wimpy can kill you. Done right, well-engineered parts can be both light and strong.
More Power, Scotty!
We love the modern chassis dyno. With proper use, it’s the perfect way to optimize a car’s power output; all potential modifications should be evaluated here.
Intake and exhaust components clearly show their benefits—assuming they work as promised—via this magical device. Same with internal modifications.
But the really good stuff comes with tuning the combination via ECU changes. A focus on wide-open throttle performance will get you most of the way there, but don’t forget to work on the part-throttle drivability that is so critical when coming off corners or navigating transitional elements. Dyno sessions can reveal other information, too, like how much to cool off the intake manifold between runs or how to properly warm up the engine for max power without encountering heat soak.
Don’t forget the rest of the driveline. You want as little power loss as possible, so synthetic fluids of the right viscosity in the transmission and differential can free up some lost power. How about your brakes? Are they dragging? Take a moment to spin the wheels and hunt for parasitic losses that could be sapping valuable horsepower from your car.
Limited-slip differentials are a great way to get all that power to the ground, and many are adjustable. Lock up too early, and the car will be harder to drive off the corner and also pushy on entry. Our take-home message here: Like everything else, fine-tune the differential’s action for maximum performance.
You’ve been recording copious notes throughout all of this development, right? Well, those notes are full of highly valuable information and are the last piece of the puzzle when it comes to getting up front.
Every race brings a new challenge. The weather may be a little off, the surface may be dirty, or the course layout may be tighter than last time. The fast guys all know how to adjust their cars for each situation before taking to the track, and your resources should allow you to do the same.
Because you did plenty of testing and took detailed notes, you’ll know how each potential change will impact your car’s performance. Don’t forget, single adjustments have multiple side effects.
For example, lowering the ride height on one end of the car will typically accomplish at least four things: add static negative camber; change the static toe setting; lower the center of gravity for less overall weight transfer; and alter the front-to-rear rake. Know how your car will react to each change. On our Street Touring Honda Civic, for instance, lowering the rear adds camber, which stabilizes the car in heavy transitions. It also removes some of the rear toe-in, which, along with the change in center of gravity and rake, frees up the car in steady-state turns. Thanks to our testing, we know that this simple tweak is great for grippier surfaces: it adds just the right amount of rotation in the big offsets without ruining the basic balance in sweepers.
When campaigning our Street Touring Miata, we found that swapping the rear anti-roll bar gave us a helpful adjustment. We traveled with two different adjustable rear anti-roll bars. Slicker surfaces and wide-open courses required less roll resistance to maintain proper camber angles and basic balance, so we’d use the smaller bar. For big concrete courses, we’d add more rear bar.
Autocross presents its own unique situation regarding setup, as changes are permissible between runs. Are your tires warming up at different rates and thus changing the level of grip found at each end of the car? Adjustable shock absorbers to the rescue. The real trick, however, is knowing what to do before encountering that situation at a major event.
And don’t forget about rain. While treaded soft-compound tires are an extremely important variable when optimizing for wet-weather performance, stabilizing the car for the reduced grip is critical for driver confidence and consistent performance. Less grip typically means less static camber, less front toe, and more rear toe. For cars that are far from 50/50 in weight distribution, the basic balance will need to be altered since weight transfer will be lower. Adjustable anti-roll bars—and testing—are key here.
Having a Plan
All of this testing and tuning may sound expensive, but it doesn’t have to be. Pooling resources with a friend or two and sharing the results can be a help, while focusing on the most important deficiencies will maximize the benefits. Those who are willing can also find opportunities for testing even during competition.
Running at an autocross where you get more than three runs? Tweak a variable after the first outings to see how the car reacts. Sure, your immediate results at that event may suffer, but you could also discover valuable information that will pay dividends at every single event thereafter. At local events, we typically never take more than two runs without making some kind of adjustment.
Do you road race? If so, are you taking advantage of all the possible test days and driver schools? And what about sacrificing a regional event for testing in order to enter a national event better prepared?
All of this development is centered around making the car the best it can be for a given situation with you at the wheel. The more accomplished drivers are better able to take advantage of a more highly optimized car, while less experienced folks are typically better served with a more forgiving car. So while it’s great to get setup feedback from the experts as you work through the process, ultimately you want the car to work best for you.
And one final note: Be a skeptic. There is no right answer. Everything is a compromise and all situations are different. Constantly collect data and analyze for further improvement. New technology and new ideas become available regularly. Remember, followers never lead. If you simply copy the fast guys, you’ll always be one step behind.
Sometimes no amount of adjustment or tuning seems to yield the expected change. When this happens, it is likely that some other knob is “turned to 11” and thus overshadowing your attempted fixes. Here are six of the most common issues that can derail the tuning process.
Bottoming Out: Lowering a car reduces weight transfer, which helps cornering due to more optimal tire use. But more is not always better when your suspension goes to an infinite spring rate as it bottoms out. Sure, properly calibrated bumpstops can help reduce this effect, but a car that is always in the bumpstops is better off with different springs and ride height settings—assuming the changes are allowed by the rules, of course.
Anti-Roll Bar Bind: Anti-roll bar manufacturers typically use urethane frame mount bushings to provide a very crisp response, but this creates a bearing surface that eventually wears out. To quiet complaints from consumers, most bars are delivered with very tight bushings. Sure, you can lube up the bushings to reduce some of the offending tension, but the grease quickly gets pressed or washed out and the bar then binds. The result is an infinite roll resistance that will absolutely destroy handling. Here’s a quick remedy: Grind some material off the flat portion of those traditional D-shaped bushings, or place a washer under one or both sides of the saddle bracket. You’ll still have to grease the bushings, but performance should be more consistent.
Bound-Up Suspension Bushings: If the rules allow the stock rubber bushings to be replaced, consider it. Urethane suspension bushings are inexpensive but require regular maintenance. Delrin is stiffer but the precision fit requires even more frequent attention. Clean and lube Delrin twice a season, and urethane once a year. If it squeaks at all, you are overdue on your maintenance.
Poorly Adjusted Brakes: Self-adjusting rear drums are a fantasy, and out-of-adjustment rear brakes aren’t doing you any good under braking. They will also negatively affect the handling when using left-foot braking techniques. Similarly, front discs that drag when hot due to sticking calipers or friction at the pad mount should also be addressed. An unusually long pull on the parking brake can be a warning sign of improperly adjusted rear brakes
Worn-Out or Improper Tires: Lots of testing time can be wasted due to crappy tires. No one wants to “waste” their good rubber on testing, but worn-out tires that are past their prime won’t provide the same performance as the good ones used in competition. Less grip means less body roll, decreased weight transfer, poor braking, a nervous disposition, and a huge waste of time. Suck it up and test on the good stuff.
Basic Maintenance: Unattended maintenance items will negatively affect performance—plugs, wires, coils, oil, lubes, bearings, bushings and so on. Even a complete engine, tranny or differential rebuild may be needed for maximum performance. All of us have been bitten by a marginal oxygen sensor, dragging brakes or uneven rotors and drums, so why enter battle in a car that’s not totally fit?
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