My car isn’t handling well. What should I change? Who do I ask? Well, if you’re like most people, you ask around the paddock. You sit and think, and then you pick up the wrenches.
Diagnosing setup changes that need to be made, and actually making them at the track isn’t easy. There’s always the pressure of time and that nagging feeling in the back of your mind, “What if I get it wrong? Then my car will handle worse.”
Suspension stories are the most-read subject in all of Speed News, so we wanted to publish a story that would provide readers with some suspension ideas that apply when you need them most: at the track.
You’re going to need to know how to measure tire temperatures to make use of these tips.
When attempting to diagnose handling problems at the track, ask yourself the questions below. It does not matter what type of car you drive, these questions will help you pinpoint the problem to find the quickest path to a solution.
• Is it a tire traction problem?
• Is the issue consistent on all corners?
• Is the problem only in corners in one direction?
• Does the handling issue persist through the entire corner?
• Is the problem only at corner entry?
• Is the problem only at corner exit?
• Is the issue only in low speed or high speed corners?
• Does the issue occur all the time or just occasionally?
• Does the problem appear after a few laps?
Here are a few scenarios and what to look at first.
Car Understeers While Cornering at Steady Throttle
Too much front roll resistance (or too little rear). Stiffen the rear antiroll bar if rear tire temps are low. Soften front antiroll bar if front tires are too hot.
Car Oversteers While Cornering at Steady Throttle
Too little front roll resistance (or too much rear). Soften rear antiroll bar if rear tire temps are hot. Stiffen front antiroll bar if front tires are too cool.
If you have adjustable aerodynamic devices in the above two scenarios and this occurs in high speed corners, the adjustment should be made with aero devices. Replace antiroll bar with wing/splitter in the above scenarios.
Handling Issues are in Turns of one Direction Only
Most likely the cross weight percentage is not at 50 percent. Diagonal weights should be equal. If they are not, handing will improve in turns of one direction but be worse in the other. Oval track cars do not handle well in right-hand turns for this reason.
Car Skates Over Bumps on Track Surface
Springs are too stiff for the track surface, Springs should be just soft enough to keep the tire contact patches on the racing surface without allowing the chassis to bottom out on the suspension or the race track.
Car Understeers at Corner Entry
The problem occurs while steering into the corner. This could be too much front brake bias. It is most likely caused by shocks.
This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the rear tires to the front tires more quickly. Front shocks could be stiffer in compression or rear shocks stiffer in rebound.
Car Oversteers at Corner Entry
The problem occurs while steering into the corner. This could be too much rear brake bias. But this is most likely caused by shocks.
This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the rear tires to the front tires more slowly while braking. Front shocks could be softer in rebound or rear shocks stiffer in compression.
Car Understeers at Corner Exit
The problem occurs while steering exiting the corner.
This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the front tires to the rear tires more slowly while accelerating out of a turn. Front shocks could be softer in rebound or rear shocks stiffer in compression.
Car Oversteers at Corner Exit
The problem occurs while steering exiting the corner. This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the front tires to the rear tires more quickly as power is applied. Front shocks could be stiffer in rebound or rear shocks stiffer in compression.
The Special Case of Front-Wheel Drive
While all of setup criteria outlined in this article apply to front-drive cars, there is one exception. Rear roll resistance is typically increased to the point that the inside rear tire is either just off the racing surface or barely loaded while cornering. Consider that most front drivers have around 60 percent — or more — of the weight on the front tires. This makes a front-drive car prone to understeer. On a typical lap, the front tires are doing somewhere around 75 to 80 percent of all the work. For good cornering balance, a front driver really only needs one rear tire. And that is accomplished by unloading the rear tire up to the point that the load is zero. Some cars will need the inside tire to do some work while cornering but most will need zero load on the inside tire while cornering.
The same effect can be accomplished by running higher than optimum tire pressures in the rear tires. This reduces the tire contact patch area and thus, traction. There are two downfalls to this practice. First, the center of the tire will wear much more quickly than is desirable. Second, some braking performance will be lost. In the absence of an adjustable rear antiroll bar, tire pressures can be manipulated to improve front-drive car handling.
A Different Way to Think!
Once the basic steady-state handling balance is established, shock tuning can provide significant improvements in lap times. To achieve this, a driver must be extremely consistent and sensitive to the balance of the car. Working with a shock engineer, I had the opportunity to spend a day shock tuning. We spent the morning getting the car perfectly balanced with camber settings, spring rates and antiroll bar stiffness. Lap times were fast and consistent. Lap times were consistent to about 0.1 percent. When we started shock tuning, the plan was to run five laps, throw out the slow and fast laps and delta (average) the remaining three lap times. Delta averages were less than a tenth of a second difference.
After the initial baseline shock test, the engineer ask a question I found surprising: “What would the car do if you drove into a turn 10 feet deeper before braking”? Also surprising was my immediate answer: “The car would understeer.” The crew changed shocks to get weight from the rear tires to the front more quickly. After the next test, the delta average lap time improved by 0.3 percent. We continued to do this several more times, each time improving the delta average lap time by about 0.3 percent. By the end of the testing, we had improved the delta average lap times by over 1.5 percent. On a 1 minute 30 second lap, that would be an improvement of over 1.3 seconds per lap. Just from shock tuning.