A setup crutch is defined as any change made in an attempt to improve the handling balance
Chassis setup crutches have been around forever, and their methods change with the evolution of setup trends. What was common 10 years ago or even 5 years ago may not be common today. We need to know what racers are doing to mask basic setup problems so we can avoid making the same mistakes.
We will outline common crutches in addition to past, present, and future setup trends for both dirt and asphalt. Both forms of stock car racing have their trends and have evolved a lot over the past few years. We'll look at adjustments teams make to try to make their cars handle better, even though they'd be better off going in other directions.
What we have definitely learned is the fastest setup on a two- or three-lap run may not be the fastest setup at the end of the race when the track surface has changed and we are running on worn and heated up tires. Our fast setup must remain fast until the checkered flag falls. The key to that end is to understand the true definition of balance so that we can have the desired consistency needed to be a winner.
We need to evaluate how we are setting up our cars, the type of racetrack we will be running on, and the length of the race. For example, if we are running 25-lap sprint races with three cautions thrown in, our desire for the ultimate fast 5 or 10 laps may cause us to deviate from a setup that must last 100 or more laps under a long green-flag run.
A race car setup crutch could be defined as any change that is intended to solve a handling problem but does not make the car faster and/or causes other problems to appear at other points on the racetrack. We will explain how some specific crutch methods work and why racers think they need these particular crutches. Then, in future articles, we will expand on each topic to explain how to develop more efficient ways to accomplish the same goals.
A driver may make adjustments to his or her driving style to try to fix a handling problem
The following are the most common setup crutches.
Driving Style The way the driver is forced to drive the car can sometimes be a crutch. How many times have we heard a driver say that the car is loose even though it appears tight on entry and in the middle of the turn? What the driver is doing, but is most likely unaware of, is steering excessively in an attempt to overcome a tight condition. This excess steering definitely creates more traction at the front tires to help balance the car. Here is the reason.
The way the driver is forced to steer the car can be an indication of a problem with the setup and is one of the top indicators that may lead to a crutched setup. A lot of research has been done on tire characteristics related to traction. Tire engineers learned that more traction is generated at increased angles of attack in the direction the car is turning. This means that more traction will be gained at the front tires as the wheel is turned farther from the direction of travel, up to a point. This is referred to as the angle of attack.
When the steering gets to an extreme angle of attack, the traction at the front tires will suddenly go away, causing a severe push. But as the steering wheel is turned a few degrees more than normal to force the front end around in a tight car, the handling balance begins to change.
As the driver enters the turn, backs off the throttle, and applies the brakes, he or she begins to turn the steering wheel and must turn it sufficiently so that the front end will come around. If the car's setup is too tight, the driver will need to turn the wheel further than would normally be necessary in a car that is neutral in handling balance.
This dirt Late Model car is very neutral in handling. Note that the front wheels are point
When the driver has turned too far, the traction balance reverses from tight to loose as the front traction begins to exceed the rear traction. At this point the car will start to feel loose. This can happen very quickly, and the driver will swear that the setup in the car is loose.
Just past midturn, the car will definitely feel loose to the driver. The exit performance off the turn will also suffer as the driver gets on the throttle and the car becomes more loose from power-induced rear wheelspin. The average temperatures of the rear tires will probably be higher than the average of the front tires due to the tires spinning with the loose-off condition.
The crew will often interpret the higher rear temps as a sign of a loose condition and think the car needs to be tightened up, but they are wrong. It is already tight, so a lot of valuable time is wasted searching for solutions to this basic problem.
A great way to quickly discover the handling balance for your car is to have the driver roll through the turn below the maximum speed. The amount of steering input needed to just drive around the turn should be mentally noted. Then the driver should take the turn at full speed and again note the amount of steering input.
If the steering wheel is turned more than when the car was rolled slowly through the turn, the car's setup is too tight. Many drivers are very surprised at the outcome of this test. A lot of time can be saved by doing this simple exercise, and it works for dirt or asphalt. For dirt, the initial entry to the halfway point in the turn is where we look for excess steering to the left for a tight car, or countersteering for a loose car.
The Big Bar Soft Spring (BBSS) setups are not always the fastest. We tried an older Midwes
Rear Spring Rates We are often in search of more bite off the corners or more aero downforce. To accomplish those goals, we can either soften the right-rear (RR) spring for more bite or stiffen the RR spring to force the nose down on the left side for better aero effect. If your car is too tight or loose in the middle, the rear springs may be too soft or the spring is split too much either way. If the setup is loose, the RR spring may be too stiff.
A common trend in dirt and asphalt racing has been to run a stiffer RR spring than we were used to a few years ago. This can be overdone, so we must compensate to correct the car's handling balance due to excessive manipulation of the car's attitude. Is this all necessary in order to go fast? We experimented and found some interesting conclusions. The first test was with an asphalt Late Model on a fairly flat track.
BBSS vs. Conventional We set up a car for a Late Model touring series (we won't divulge which one) in which the Big Bar and Soft Spring setups were the trick. This series even had a few teams with traction control (not our conclusion, but the consensus of most teams and the officials). We participated in a test day with most of the top cars in the series present.
We decided to deviate and see what would happen if we set up the car just like a typical mid-'90s Midwest flat-track car, using a 350-pound LF, a 325-pound RF, a 185-pound LR, and a 175-pound RR spring. This is basically the flat-track setup I developed for Brian Hoppe's team when he won the 1999 RE/MAX Challenge Series. We also set the crossweight to around 58 percent. We practiced on tires that were used in the previous race and never put on stickers.
Our lap times were as fast or faster than the other cars on not-so-fresh tires. After the other cars had made their sticker runs and put about 20 more laps on those tires, we were still as fast as them, using our 200-plus-lap tires. On longer runs, we were consistently quicker toward the end of the runs, and we got off the corners better than even the T/C cars. Our driver could flat-foot the car off a slippery Turn 4 all day long.
We attended a closed test in which we changed everything we could to see what the results
Dirt Car Setup Test We recently attended a closed test with dirt Super Late Model cars. We found interesting trends, but we will report more on this test later, when the data has been properly evaluated.
We started out with what would be described as the current trend in setups. The Panhard bar was attached to the left side of the chassis and was angled with the left mount much higher than the right mount. The left side upper trailing arms were set higher, and the LR spring was mounted in front of the rear end. The front springs were 400 LF, 375 RF, and the rear springs were 275 LR, 275 RR. The car was evaluated for front moment center location, and throughout the test the car turned in well and was neutral in the middle of the turns. The track was moderately slick, and the main problem was getting bite off the corners.
We changed all the bar angles left and right, changed the lift arm shocks and spring, and even replaced the right lower trailing arm with a pushrod. None of those changes produced better lap times, and some adjustments felt bad to the driver.
Then we did something crazy. We reversed the Panhard bar from left chassis to right chassis mount. This configuration completely changed the attitude of the car. Instead of the rear of the car being high and the LR tire moving forward, the car sat low in the turns, both rear tires tucked inside the wheelwells, and the car ran the same lap times. The driver actually went a few tenths faster down low, but moved up after two laps.
In our dirt test, we placed the rear trailing rods in all the combinations of holes to rec
The driver liked the feel of the car, but traction off the corners was not necessarily improved. The surprising result was that the lap times did not fall off or get better. The car remained as fast as before and was consistent. The one difference noted was that the LR tire was working more and getting hotter. We will be doing more with this ongoing dirt testing and reporting the results in future issues of Circle Track.
The point here is that whatever the trend, we have to make it work to be consistent and the car must be balanced with all the qualities that will make it fast throughout the race. Don't be afraid to experiment. Our asphalt car did not have the low left-front attitude of the BBSS setups, but it was as fast as those cars.
Front Spring Rates The trend in asphalt racing is to run very soft springs in the front of the car. But there is a limit to how much benefit you get with very soft springs, and the top professional teams have discovered that full coil-binding is not beneficial to good handling.
Again, this is a product of going too far with a good thing. The front end must be low for maximum aero effect, but if the springs are bottoming out or the chassis is contacting the track surface, the car won't handle properly. Handling is the key to going fast.
If you are going to experiment with spring changes at the track, make sure you preplan you
Dirt track racers have softened up quite a bit over the past five years or so. Street Stock cars that used to run 1,000 to 1,200-pound springs on the front are now down to 850 to 950-pound springs. The norm for springs in the touring dirt Late Model cars used to be 500 LF and 550 RF. Now we see those rates down to 400 to 450-pound springs, sometimes with a stiffer LF.
Dirt teams that have softened the front springs to as low as 600 pounds on Street Stock cars and 300 to 350 pounds on coilover-type Late Model cars have found those rates to be too soft when the car bottoms out or there is too much camber change. This is yet another case of having too much of a good thing.
The Front Geometry Front-end geometry is one area in which changes across the board have made a huge difference in all forms of racing. From Formula One to Street Stock, much research has gone into the value of proper geometry and success in making refinements.
The neat thing about front-end geometry is that what has been tested and proven works with all the setup trends. Good dynamics and proper camber change characteristics are needed in dirt and asphalt (for all classes in each) and helpful for BBSS or conventional trends.
The reason that MC design is valid for all race cars is that the front moment center location controls much of the dynamics of the front suspension. This invisible intersection point is the bottom of the moment arm, and its lateral and vertical location regulates the stiffness of the front end like no other setting. The MC should be designed correctly for each type of race car and for each particular track.
We experimented with front moment center adjustments on a dirt Late Model and found that t
Moving from a moment center width of 0.0 to 10.0 inches right of centerline is like stiffening the front end by an average of 175 pounds of spring rate per side. That's like going from 275-pound springs to 450-pound springs. If you are trying to go soft on the front end, you must consider the MC design along with using softer springs.
The Rear Moment Center Height Many teams don't appreciate the value of the rear Panhard/J-bar as a tuning tool. Some classes don't have a choice in rear MC heights. The stock classes that run metric four-link rear suspensions must live with a very high rear MC that is very hard to adjust. To compensate, they must run a large spring split with the RR spring rate 50 to 100 pounds less than the LR spring rate.
Just like the front MC, rear MC is the bottom of the rear moment arm. If the Panhard bar is set too low or too high for your springs, the rear of the car will not be in sync with the front suspension. This causes either a tight or loose condition.
The bar angle has an effect on load transfer due to its reaction with lateral force. On dirt Late Model cars with bars mounted on the left side of the chassis and a lot of angle pointing the bar toward the RR tire contact patch, a lot of load ends up on the RR tire and the rear of the car rolls up while trying to flip over the rear end. As a result, the rear end steers excessively to the right.
This arrangement will help a tight car get around the corner, but we can't help thinking that this is a crutch. What if we worked on our setups and our geometry in the front end so that the car turned better? Then we could reduce the Panhard bar split, lower the rear MC, reduce the rear steer to the right, and maybe move the Panhard bar over to the right side of the chassis.
Many dirt cars have the Panhard bar attached to the left side of the chassis and mounted h
The CrossWeight Percentage Having an excess amount of crossweight, or wedge as it is referred to in dirt racing, causes too much weight to be supported by the left-rear and right-front tires and can cause a car to be tight in, through the middle, and off the turns.
We can work within two or more crossweight ranges to make our cars neutral in handling. Within each range, there is a percentage that balances the handling (not the dynamic balance) so that the car will be neutral at midturn.
The ranges and numbers depend on the front-to-rear percentage of weight distribution. The more rear percentage the car has, the more crossweight percentage you need in each range to make the car neutral. If I move weight in the car and go from 50 to 51 percent rear weight distribution, I need to go from 52 to 54 percent of crossweight to keep the car neutral.
Think about this. A team has trouble with a tight-loose condition in which the car is tight and the driver oversteers into the loose-off condition we described earlier. They add rear weight to tighten the car, and all of a sudden the loose-off condition is gone. They think they've added bite with the added rear weight, but in reality, they have loosened the car to make it more neutral in the middle of the turns by not adding crossweight with the front-to-rear percentage change.
Crossweight that is too low is a distinct indication of a tight car. If a car really needs 51.9 percent of crossweight to have proper weight transfer and is able to run only 49.8 percent, we know the team had to take cross out of the car because the setup was tight.
There is an optimum percentage of weight distribution that will make the car neutral if the setup is dynamically balanced. Remember, a neutral car is not necessarily a winning car. It must remain neutral throughout the entire race, and having dynamic balance makes that happen.
Conclusion The use of excess steering input, low crossweight, rear steer, or any of these crutches intended to make your car turn are indications that other problems exist and need to be fixed. What the car needs is an arrangement of spring rate layout, front geometry design (including moment center placement and camber change), Panhard bar height (rear moment center height), and correct weight distribution that will work in combination to provide a fast and balanced setup.
Once these areas of setup are correctly identified and made to work together, the car will give the team what it wants, which is a fast and consistent handling package that the driver can use to win races. Being able to identify the crutches and knowing which areas to look at to correctly solve your handling problems makes the process much easier.
If you can identify your driving and setup crutches and find the proper fixes for your handling problems, then your program will move forward and your team will be much more successful. If you've ever wondered what makes a championship team able to adjust and run well anywhere they go, it is largely because they have learned how to identify the difference between meaningful adjustments and crutches.