Crutches are born in the pits as racers try to help each other with their chassis problems
You're hammering around the racetrack in your race car and it's just not handling. You feel like it's tight getting into the corner, which prompts you to turn the front wheels in, but the car slides up toward the wall as you negotiate the entrance to the middle of the corner. You have tried a few changes but nothing seems to help.
At a loss as to how to correct the problem, you walk around the pits seeking some wisdom from fellow racers. They throw out suggestions like, "Bolt 50 pounds of lead on the rear bumper," "bolt a tie-down shock on the left rear," or the classic, "increase the stagger between the rear tires." You might try one of these or all of them. You might even have some success at getting more balance in the car upon entry into the corner. But what you don't know is that these are all "crutches" that racers think correct a problem but actually just mask it enough to fool them.
Because of what these crutches do to the overall performance of the car, they hold cars or drivers back from improving their performance. Some examples of crutches are driving styles (throwing the car into a corner to loosen it up), hanging weight off the rear of the vehicle, a super-stiff right front spring, a longer right side wheelbase, rear steer to the right, tons of brake bias, and more. Do these sound familiar? They probably do because most racers use them.
If you want a great example of a tight or pushing race car, check out car #5 trying to avo
This story is the kickoff to a regular section in Circle Track about these mythical suspension and chassis fixes we call crutches. We're going to debunk many methods racers use on a daily basis supposedly to go faster around the racetrack. While most of these crutches will mask a problem enough to get around the track, they aren't the best solutions because they limit the overall performance of the vehicle. If you truly want to win, read these articles with an open mind and figure out how to incorporate the optimal solutions for your car to go faster, instead of relying on the monkey-see, monkey-do crutch fixes all the other racers are using.
We will call on many sources for useful information but rely heavily on Bob Bolles, the mastermind behind the Chassis R&D software and a real student of great suspension and chassis knowledge. He gets to ask some of the best racers in the circle track world the "stupid" questions and learns something every day because of it. We like his view on racing knowledge "The worst thing you can do is decide you know it all. I don't believe there is a way to know everything about making a car as fast as possible, but there are basic principles the quick race cars operate with. I have been able to clarify what some of these are from working with many winning racers. When someone brings a new idea to me, I ask as many questions as possible, weigh the results against my previous knowledge, and try my version of that technology on the race track. It's critical to understand how a change affected the car. Usually, that understanding is the hardest thing to achieve."
A loose race car will do what #15 is doing here-point toward the infield as the rear end s
It's important to define what is meant when racers say their car is "handling" well. Just so everyone is on the same page, "handling" in the case of a circle track race car means that as a driver, you can drive the car down into the corner without it being loose (this would cause the car to point toward the infield) or tight (also called pushing, which would point the car toward the outside wall-with wide eyes!). Both of these conditions limit your corner speed, which slows your straightaway speed, which makes for slow lap times. Since we all want quick lap times and fast straightaway and corner speeds, we want a car that's balanced between tight and loose, a car that is neutral through the corners. A neutral car that is set up correctly (no crutches) will be affected less by changing track conditions than a car that has been crutched to get neutral.
The three main areas where a race car is prone to have these problems are entry to the turn, through the middle of the turn, and exit from the turn.
To determine whether your car is tight or loose upon entry into the corner, roll through t
Driver Steering Crutch
There are many mechanical crutches to talk about, but there also are many human crutches the driver can be fooled by when negotiating the racetrack. Sometimes these crutches allow a racer to complete a race without coming in to make major suspension tuning changes, but usually they are unknowingly used by a driver to get around the racetrack. More often than not, these crutches limit the performance of the driver and car.
The most common driver crutch arises as a reaction to the way a race car needs to be driven to get around the track. Simply put, as the race car enters the corner, the driver turns the steering wheel until the car reacts positively in the direction of the turn. Often, the driver will claim the car is loose in the middle of the corner and upon exit. But often drivers are not cognizant of the fact that they are turning the front wheels too much to the left to overcome a tight condition on entry to the corner.
Determining the track banking is as easy as laying a straight 10-foot bar on the surface a
To understand this, we need to add some information about the characteristics of tires in relation to traction. Tire engineers have learned that a tire will generate more traction at an increased angle of attack to the direction the car is turning. This means the front tires gain traction as the steering wheel is turned...up to a point. When the front tires are turned to an excessive angle of attack, they will give up all their traction, causing a severe push or tight condition in the race car. Normally, as the steering wheel is turned to muscle the front end around on a tight race car, the handling balance of the car is reversed as the front traction becomes greater than the rear.
Here is the scenario: As the driver enters the turn, he simultaneously backs off the throttle, applies the brakes, and turns the steering wheel. The steering wheel is twisted enough so the front end comes around. If the car is set up too tight, the front wheels are turned more than would be necessary if the car's handling balance neutral. Because of the excessive angle, the front-wheel traction is greater than the rear-wheel traction and the car begins to feel loose. This can happen so quickly that the driver will swear the car is loose.
The driver will feel a loose condition in the middle of the turn and the exit performance will suffer because, as the driver gets on the throttle, the rear wheels are likely to spin. This slippage increases the temperature of the rear tires, which, once the car is back in the pit and the tire temps are read, might fool the crew into thinking the car needs to be tightened up.
Changing the Panhard bar mounting point changes the rear roll center, which might be neede
Determining Whether Steering Crutch Exists
Here's a great way to quickly discover just what the handling balance really is for your car: Ask the driver to roll through the turn well below the maximum speed. The amount of steering input needed just to drive around the turn should be mentally noted. Then, get the driver to roll through the turn at near maximum speed without excessive braking or acceleration, again noting the amount of steering input required. If the steering input is higher at the increased speed, the car is set up too tight. Many drivers are very surprised at the outcome of this test. You'd be surprised how much time messing with the setup can be avoided by doing this simple exercise.
Why Your Car Might be Tight
In descending order of importance, here are some classic reasons your race car might be tight entering the corner.
• The rear springs are too soft. This is true especially with the right rear. This will make a car tight because the springs allow too much roll in the rear of the car, which binds up the front end, overloading the right front.
What's the worst that could happen if your driver keeps crutching the race car? Well, the
• The front springs are too stiff. This makes the car tight by not allowing the front suspension to roll and work with the rear. You want both the front and rear of the car to pivot around the roll centers in unison, or the car binds up and is tight.
• The Panhard bar is set too low. If the bar is mounted too low for the springs you have chosen to run, the rear of the car will roll more than the front, making the car tight.
• The front roll center (RC) is too far to the right or left of the centerline of the race car. If the front RC is too far left, the car will roll excessively in the front and the right front camber will change too rapidly, causing a loss of grip in the tire. If the RC is too far right, the front end will not want to roll and if the rear rolls free, the car will bind up, much the same as having springs in the front that are too stiff.
• The crossweight percentage (right front + left rear) is too high. Crossweight is the weight on the right front and left rear tires. Too much of it will cause a car to be tight as the right front gets overworked.
• Using excessive Ackermann angle in the steering system. Some racers have steering systems that create too much Ackermann angle gain (one wheel steers more than the other to account for the different radii they experience), which causes the car to have too much toe-in or toe-out in the middle of the turn. This will cause the front end to skate and push, which makes the car feel tight.
Notice the angle these dirt cars are negotiating in the corner. They are hardly sliding ou
• Running with too little stagger in the rear tires. Insufficient rear-tire stagger will cause the car to "point" toward the outside wall upon exit. There is a correct amount of rear stagger for each track based on tire diameter versus the radius of the track versus the track banking angle. Also, too little stagger usually will drive the car to the right in the middle of the turn.
Get Ready for More
This is probably more information than you can process, but we're just getting started. Look for the next race car crutches installment next month and get ready to learn more about why you're not going faster.
Is There a Difference in Dirt vs. Pavement Chassis Setup?
For years, chassis setup for circle track cars has been accepted as being different for pavement and dirt track cars. But we've discovered that the same theories and setups are common across the board.
Bob Bolles (right) confers with dirt Super Late-Model ace Kevin Weaver at Eldora Speedway.
So, you ask, how can that be if dirt cars slide the rear end out entering the corner? According to one of the top drivers in the ever-competitive Hav-A-Tampa Super Late-Model dirt car series, "sliding a dirt car into the corner is to help the car turn in, but sliding your car sideways in every corner is not the fast way around the track. For quicker lap times, we are constantly working on the suspension, steering, and chassis to get the car to turn in with less angle in the slide of the rear end. Sliding the rear scrubs off speed and uses the power of the vehicle to negotiate the turn instead of pushing the car forward. As racers all continue to learn more about chassis setup and the like, you are going to see less angle in the power slides into the corners. This is because racers are figuring out how to set up dirt cars to drive around the track, instead of slide around-and driving is quicker than sliding.
Crutches to Watch for in the Future
Plenty of crutches are being employed by racers every day, so this series of technical articles exposing these crutches is going to go on for many months. Look for stories on crutches such as extreme right front camber, excessive stagger, rear steer to the right, spring mounting location on the chassis, shock absorber misuse, excessive toe settings, too-stiff right front spring, longer right-side wheelbase, and out-of-proportion corner weights, among others. This list could be longer, but these are some of the most common crutches and will keep all of us busy. We plan to support these articles with documentation from real track testing of these theories to show how they work in the real world of racing.