• The 24 Deadly Sins of Chassis Tuning

    The 24 Deadly Sins of Chassis Tuning



    Written by The Staff of Motorsport Marketing
    From the March 1999 issue story by Don Alexander • Illustration by Ruben Cueto

    Picture this: At the race track, you’re unloaded and ready to go for the first practice session. After the session is over, you feel lost because your car’s handling is way off. You make changes that should help, but in the next session, the car feels even worse. The same scenario continues for the remainder of the event, and you’re very unhappy with the result.
    There is a good chance that one or more of the following chassis tuning sins is the culprit behind your situation. Any one of these problems can be your undoing; most racers are guilty of breaking several of the rules regularly. Here’s a primer to help you spot—and correct— these most common causes of bad handling. May you find salvation at the checkered flag.

    Thou Shalt Have a Solid Baseline

    One key to being fast and competitive is repeatability—and you cannot repeat results if you do not know where you started. That’s why you need a good chassis baseline. You can start with the baseline settings recommended by your chassis builder or suspension guy. If you have the experience, however, you can create your own. And best of all, if you have records from previous outings at the track you are headed to, you’ll have a head start.

    You should at least record the following: frame heights, crossweight percentage, rear and left—side weight percentages, all four tire circumferences, fuel load, gear ratio, wing settings, spring rates (bar neutralized), shock valving, toe, alignment, pinion angle, Panhard bar height or Watt’s linkage settings, and any other settings than can affect the handling.

    Thou Shalt Not Prepareth at the Track

    This happens too often. You run out of time or have inadequate help before a test or race, so you end up preparing the car at the track—or at least finishing the job there.
    It is very difficult to create a good setup at the track; you can do a much better job at the shop. And track time is expensive for a test day; wasting that time playing in the pits is not effective. If you’re prepping your car at the track during a race weekend, forget any chance of a good result.

    Thou Will Taketh Tire Temperatures

    Tire temperatures are your link to what goes on between the tire contact patch and the track surface. I find it difficult to make sound tuning decisions without tire temps. Tire temperatures should be taken religiously every time the car comes off the track—even after a race.

    Thou Will Take Segment Times

    Time around the track is gained in very small increments. Chassis adjustments can make a car faster (or slower) around the track, but may cost time in certain areas of the race track. Knowing this can add to the data available for you to make sound tuning choices.
    The only way to accomplish this is to record times in several segments of the race track. (For example, timing how long it takes to get through a series of corners.) You don’t need to take times in every segment on every lap, but taking segments at various points for each session will prove very valuable, especially in testing.

    Thou Shalt Not Have Excessive Crossweight

    Crossweight, the measure of right front and left rear combined weight versus total car weight (both with driver), is a usefiJl tuning tool. In road racing or autocrossing situations, excessive crossweight will help handling in one direction but hurt in the other—and it hurts more one way than it helps the other way. Crossweight should be set at 50 percent, if possible, and never less than 49.5 percent or more than 50.5 percent.

    Thou Shalt Keepeth Thine Records

    This may be the most costly sin of all. There is just too much data to track if you don’t write everything down in an organized way. Even if you luck into a good setup, without records you will be unable to repeat it without going through the complete process all over again.
    The best time to record notes is back in the shop after a race. If you have a good race setup, these notes will tell you how to get back to it the next time you race at that track under similar circumstances. And if the results were not so good, at least you know you need to do something different.

    Thou Shalt Not Listen to Too Much Advice

    Everyone is a setup expert, or so most people would have you believe. If you want to be successful, then you must learn enough to make your own tuning decisions within your own team. Listening to advice from others is one thing, but putting it to use is another.
    Even if the person offering advice is very knowledgeable, that person likely does not know your situation, preferences, resources or needs. Most often, the person offering advice is less knowledgeable than you are, and usually only knows a couple of things that could cure your perceived problem.

    Thou Will Haveth a Game Plan

    Any plan is better than no plan at all. Take the time to create a game plan for each race, beginning with your realistic objectives, maintenance schedules, testing and race strategy. Remember that part of a good game plan is the flexibility to alter the plan as needed. Usually, no plan equals no result.

    Thou Shall Determineth the Exact Problem

    A handling problem can occur anywhere on the track. Is it corner entry, mid-turn or corner exit? Does it happen everywhere? If a problem occurs in one place, does it result in a different problem someplace else? The classic example of this situation is comer-entry understeer that a driver over-compensates for at the exit of the comer, creating an oversteer condition. The driver says the car is oversteering, but the real problem is the corner-entry push. Adjusting for the oversteer will make the problem worse.

    Thou Shalt Not Have a Suspension Bind

    Suspension binds create an inconsistent handling situation. If a bind is present, it is just about impossible to properly tune the suspension. If the car does not respond the way you think it should to suspension changes, check for bind in the suspension. Checking for binds should be part of your routine setup process.

    Thou Shalt Not Have a Dead Shock

    A bad shock can be very difficult to feel. Check the shocks if you cannot get the chassis tuned effectively. Feel for a dead spot or lack of resistance in both rebound and compression.

    Thou Will Set Thine Car Up According to Driver Feel

    Often, the fastest setup for a given car is too aggressive for a driver without some experience. When the suspension is too stiff, especially the shock valving, it is difficult for the driver to feel what the chassis is doing. The car reacts too quickly for the driver to sense what is occurring.
    Softer springs and shocks, while slower for the experienced driver, may be faster for the inexperienced driver.

    Thou Shalt Not Make Corner Weight Adjustments at Only One Corner

    To adjust comer weight percentage, you must change frame height. Suspension geometry is designed to work best at a certain frame height, and changing the frame height can alter the suspension geometry in a negative manner.
    Making one big change at one comer can cause this problem to happen. The trick is to make small changes at all four comers. Instead of putting a turn in the right front, put a quarter-turn in the right front and left rear, and take a quarter-turn out of the left front and right rear.

    Thou Shalt Not Try to Cure Handling Problems With Only One Element

    Any handling problem can be changed by adjusting several different parts on a car; it is ineffective to change only one or two items to improve the handling. Often engineers, whether their specialty be shocks, tires, springs, or whatever, will try to cure a problem by using what they know best.
    This is often not the most effective way to solve a problem. It is important to look at the entire system as a whole, then make changes that suit the system best and offer the most favorable compromise.

    Thou Shalt Not Make More Than One Change at a Time

    While more than one suspension adjustment may be needed to cure a handling problem, it is always best to make only one change at a time. Make a change, and then go test.
    Making more than one change at a time can produce results that are difficult to analyze. Which change helped, and did one change actually hurt?

    Thou Shalt Not Stray From Recommended Frame Heights

    This can cause binding in the suspension or, at a minimum, cause undesirable suspension geometry. Don’t stray too far from home.

    Thou Will Carry a Consistant Fuel Load

    Changing fuel load will always be a setup and tuning problem. As fuel is burned off, handling will change as the weight in your fuel cell changes. If you do not tune with a constant fuel load, your data will be inaccurate and the results misleading. No more than a two-gallon fluctuation is acceptable. One gallon is a better mark. Remember that each gallon of gas weighs about seven pounds.

    Thou Will Establish Good Crew/Driver Communication

    If the crew and/or driver are not sure of the concepts of tuning and are not clear about the language, all sorts of problems can occur. Everyone on the team needs to be on the same page.

    Thou Will Control Over-driving

    If a driver is over-driving the track or car setup, most of the data, whether from the driver or tire temperatures, will be less than accurate. Over-driving not only abuses the tires, but also masks real handling problems.

    Thou Shalt Not Make Changes Which Are Too Big

    If a change is too big, it can cause handling problems that are worse than the ones you already have. On the other hand, a change too small can be difficult to detect by the driver or on the stop- watch. Big changes include altering more than two numbers on shock valving, more than 15 percent in spring or bar rate, more than two percent crossweight or more than a 1/4-inch change in ride height.

    Thou Must Understand the Whole System

    Understanding the whole system is very important. The key is to understand how any change affects the tire contact load and traction. Always thinking in terms of tire contact patch load and traction will help you focus on making the best change possible for the situation.

    Thou Must Recognize Changing Track Conditions

    Track conditions constantly change. The car may get faster during the day even though the lap times are slower, because the track may be slowing more quickly than the car is getting faster. If in doubt, return to the starting setup to see how the track has changed.

    Thou Shall Measure Accurately

    Recording inaccurate measurements is as bad as not keeping place. This can lead to all kinds of problems.

    Thou Will Not Chase Old Tires

    At some point, tires get too hard to be fast. There is a point beyond which, no matter what you do, the car will not get faster. Chasing an old set of tires is ineffective.