Setup The Race Car Camber: Camber is the inward or outward tilting of the front wheels. Negative camber is the tilt of the top of the wheel towards the center of the vehicle. Positive camber is the tilt of the top of the wheel away from the center of the vehicle. Camber adjustments are made to maintain the maximum amount of tire tread on the ground during suspension movement and body roll through the corners. Proper camber adjustments are critical to achieving maximum cornering speeds. When camber is set correctly it allows the entire surface of the tire to adhere to the track maximizing the tire contact patch when taking a corner at high speed. Proper camber adjustments are achieved by reading tire temperatures. The goal here is to get even temperatures across the whole tire. On all tracks except road courses you need to run with negative camber on the right front and positive camber on the left front. This aids in getting the car to turn left. How much camber you might ask? It varies depending on track banking, spring stiffness, body roll and other considerations. Generally add just enough camber so the inside of the RF tire runs a degree or so hotter then the outside. Then backup a notch to get the tire temperatures even again. The decision on the LF camber is a little more difficult. Adding positive camber to the LF doesn’t help quite as much on ovals as adding negative camber to the RF. More importantly, if you hit the apron with a lot of positive camber on the LF there will be a tendency to lose control of the car as the LF gets more of grip and the RF looses grip. This will cause the car to turn in hard toward the apron and only makes the situation worse. Be a little more conservative when working with the LF camber. Work mainly on keeping the car under control when you get a piece of the apron. When competing on a road course like Watkins Glen or SearsPoint, or any track where your making both left and right handed turns, you will typically want negative camber on both the LF and RF tires. The reason for this is the outside tire on a corner supplies most of the cornering force and will therefore dominate that corner. By adding negative camber to both tires you help the car turn better in both directions. Rear camber is not as critical as front camber due to the fact that the rear-end is a solid axle. The same theory holds true though as you might want negative camber on the RR and positive camber on the LR on an oval track. On a flatter track you may not need any camber in the rear. Stagger built into the Goodyear tires will naturally create some negative camber in the RR and positive in the LR as is. Knowing how to read and understand tire temperatures will be the determining factor in how much camber to set in your wheels. In fact it’s the only way to properly adjust for correct amount of camber. Since you must constantly monitor tire temperatures you will always be readjusting camber (at least in the front). Just when you think you have your tire temperatures and camber perfect, you’ll change a spring or tire psi to find more speed, or the weather will be different forcing you to make some adjustments elsewhere. All that hard work you spent on achieving those perfect temperatures will have to be thrown out the window and the whole process begins once again. One final thought, if the tire temperatures on the inside and outside are not even, then your are going to increase wear and a shorter life of that particular tire. Too much camber will decrease the size of the tire contact patch and reduce the amount of cornering force available. How camber effects the handling of the chassis: More negative RF camber allows the car to turn into a corner quicker, which will loosen up the chassis. Less negative RF camber takes away some of the pull to the left. The car won’t turn as quick into a corner, which will tighten the chassis. More negative LF camber will reduce the pull to the left while tightening the chassis from the middle out. More positive LF camber will increase the pull to the left and allow the car to turn into a corner quicker loosening the chassis. More positive camber in the RR will loosen the car from the middle out. More negative camber in the LR will loosen the chassis entering a corner. Caster: Caster is a major factor which provides a vehicle with directional stability. Directional stability is the ability of the vehicle to travel straight ahead with a minimum of steering corrections by the driver. Viewing the car from the side, Positive caster is the backward (toward the rear of the vehicle) tilt of the steering axis and Negative caster is the forward tilt of the steering axis. Caster is measured in degrees of angle, the amount the steering axis is tilted from a true vertical axis. Do not confuse this with camber which is the inward or outward tilt of the wheel. To understand the principle and effect of caster on the steering system, let’s examine the ordinary household furniture caster. When a piece of furniture on casters is pushed, the casters turn on their pivots until the wheels are in line with the direction of force applied and the wheels are trailing in back of the pivot. In this position, the furniture will roll easily and in a straight line. Therefore, it can be seen that when a force is applied to the pivot it tends to drag the wheel behind it. The reason lies in the fact that the projected centerline of the caster pivot strikes the ground in front of the contact patch of the wheel. This simple principle applies to a vehicle. If the steering axis pivot is tilted backward (toward the rear of the vehicle), the projected centerline of the pivot strikes the ground ahead of the contact patch (which is positive caster). When the vehicle is driven forward, the pivot is behind the wheel, giving the car directional stability. When setting your chassis you’ll want to tip the top of the wheels back adding positive caster to provide you with that straight ahead directional stability. Under NO circumstances do we use negative caster, even though the adjustment range is from -2.0 to +6.0. How much caster do I need? The amount of caster set into the chassis depends on two factors: The amount of weight on the front wheels and the feel of the steering effort to the driver. The amount of positive caster depends a great deal on the speed of the race track and the amount of weight on the vehicle front end. The lighter the weight on the front end, the greater the amount of positive caster. For example, a Porsche road racing car with only 40% front weight may have 61/2 degree positive caster where as a NASCAR stock car with 51% front weight may have only 31/2 to 4 degrees positive caster with both cars running on the same track. Race cars that weigh 3500 pounds and more, front caster angles run between 3 and 5 degrees positive. The more positive caster a car has, the greater the straight line stability it will have. The car will have greater high speed stability and require less constant attention on the part of the driver. The faster the track gets in terms of speed, the greater the positive caster setting. Cars running at Daytona and Talladega have as much as 41/2 to 51/4 degrees of positive caster on the RF wheel. On shorter tracks where speeds are more moderate, the RF caster is from 3 to 33/4 degrees positive Another factor to consider is the steering device you maybe using. (i.e. force feedback) The more positive caster the more feedback you will feel as a driver. More caster can also provide a more difficult steering effort, especially with a force feedback wheel. So why not crank the caster positive as far as it will go? Because too much positive caster also has it’s drawbacks. When you turn a car left with positive caster the LF rises while the RF drops. This changes the weight on all 4 corners of the car. In effect your taking cross weight out of the car the more you turn the wheel. The more positive the caster, the more cross weight there is being removed. The more cross weight you remove the looser the car will get. Caster stagger: Another element that must be considered is the caster split, or caster stagger as it is called. Caster stagger is simply using different settings on the LF wheel than the RF. At any track where the car is making only left turns, the caster is staggered with more positive caster on the RF than on the LF. The reason for using caster stagger is to help the wheels steer themselves to the left in the corners. For short track racing, many drivers prefer to use as much caster stagger as possible (up to a maximum of about 4 degrees). The greater the amount of stagger will allow the driver to almost allow relax the steering wheel completely entering a turn, letting the car steer itself into the corner. The drawback of using so much caster stagger though is the increased effort in crossing the steering wheel over to the right to correct for oversteer. The greater the stagger, the greater the effort required to turn the wheel back past the straight ahead centerline of the steering wheel. At higher speed race tracks, the more the caster stagger closes up. Daytona and Talladega for example drivers generally use no more than 11/2 degrees of caster stagger. The amount of caster stagger is totally up to the driver’s preference and several settings should be tried before the final setting is arrived at. How caster effects the handling of the chassis: More positive caster will loosen the chassis the more the wheel is turned through a corner. The car will pull to the side with the lower amount of positive caster. The higher the caster stagger, the easier the car will turn into a corner. The less steering effort required. This will tend to give you a loose feeling upon corner entry. Front toe-out: Toe-in or toe-out is the difference in distance between the extreme front and extreme rear of the tires when measured at spindle height. Front toe-out is utilized to help minimize tire scrub and rolling resistance, while cornering. It’s used in oval racing in order to produce more optimum slip angles for cornering. We can make adjustments that range from -0.200″ of toe-in through 0.200″ inches of toe-out. Never use a toe-in condition. The majority of setups usually require a setting of less than 0.125″ inches of toe-out. Don’t run anything less than 0.025″ and no more than 0.175″ inches max. toe-out on any track. Excessive amount of toe-out will cause tire scrub both on the straightaway and cornering. Warning, running too much toe out will scrub off speed down the straightaway. At large tracks like Daytona and Talladega you would minimize toe-out and at small tracks maximize it. Another consideration, adding more toe-out will add Understeer to the chassis at entry and at mid-corner. To monitor toe-out, read the tire temperatures. Toe-out is read on the inside edge of the RF and the outside edge of the LF. If you have too much toe-out these areas of the tires will heat up more. You should set camber first then check this condition for toe-out. Start with an adjustment of 0.050 and you will be close. Adjust the toe-out only when the rest of the chassis is close to being correct. Tire pressures: Tire pressure is another adjustment that will aid in achieving the best possible grip. As a general rule, lower tire pressure generates more grip, but at the expense of higher temperatures and more rolling resistance. Tire temperatures play a critical role in the effectiveness of a tire and you should try to keep them in the range of 190 to 220 degrees. If a tire is too cold, it will become stiff, reducing the stiction forces. If it becomes too hot, it will begin shedding rubber, decreasing grip and adding to the wear, while reducing its life. Rolling resistance is a force that opposes the rotation of the tire, effectively slowing the car down. Increasing tire pressure will reduce the rolling resistance while, increasing the top speed of the car. However, it will typically reduce the grip for that tire as well. A third factor that comes into play with regard to tire inflation is the spring effect of the tire. 1 lb of air pressure adds an additional 15 lbs of spring to the sidewall of the tire, effectively stiffening the suspension on that corner of the car. A fourth factor to be aware of, when dealing with tire pressures, is that you are also changing the weight of the car on that corner. By raising or lowering tire pressure your changing the ride height of the chassis. Changing the ride height adds or subtracts weight from that corner of the chassis. This is another way that tire pressure can actually react like a spring. Adding more tire pressure makes that same spring a little stiffer. Lowering tire pressure will make that spring a bit softer. In other words if you lower the RF tire pressure your also making the RF spring weaker. Making the RF spring weaker will loosen the chassis. When you understand how springs work, you’ll be that much further ahead to understanding how tire pressures work. This will become very important to be able to adjust the chassis during a race. Tire pressure is simply how much air you have in the tire. The hotter tires get, the more they expand. Air contains moisture. Moisture becomes steam as the air gets hot and increases pressure. Some teams actually don’t use air in their tires, they use nitrogen. Nitrogen is preferred over air because it doesn’t expand as much with temperature changes because it doesn’t contain moisture. Since it’s impossible to remove all the moisture from a tire, it will still change pressure as temperatures rises. This can be noted after running a test session and checking your tires both hot and cold. When tires expand it changes the size of the tire which in turn changes the weight on that wheel. This can be either a negative or positive situation depending on your chassis needs. Tire pressures can be adjusted on all 4 tires from as low as 5 psi, to as high as 15 psi. Improper tire pressure can cause an ill handling car. Correct tire pressure can be determined by reading tire temperatures. A tire with a temperature reading higher in the center of a tire indicates an over-inflation. A tire with a lower center temperature, when compared to the inside and outside of a tire indicates a under-inflation. Over inflated tires will have a tendency to make the car tight. Tires are the only adjustment we can make during the race that allow you to compensate for differences between entrance and exit problems. They work in much the same way as shocks. Increasing pressure is like stiffening a shock and will decrease grip on that corner. Lowering pressure is like softening a shock, increasing grip on that corner. To fix a loose condition into a corner: Increase RF tire pressure and/or decrease RR tire pressure Push all the way through the exit of a corner: Increase LR tire pressure and/or decrease LF tire pressure Tire stagger: Altering tire pressures allows us to slightly modify the stagger. Stagger is the circumference of the right side tires compared to the left side tires. The best way to describe stagger is by using a white Styrofoam coffee cup. You know, the kind that is bigger around on the top than on the bottom. Take that cup and lay it over on it’s side on a table. Now push it along the table letting it roll. You see how it turns in one direction. This is stagger. Imagine the larger side of the cup as the right side tires and the smaller side of the cup as the left side tires. See how it turns left? Stagger on a race car works the exact same way. By increasing tire pressure on the right side, or decreasing pressure on the left we add stagger to the chassis allowing the car to turn left better through a corner especially under acceleration. I wish we knew exactly how much this works in the game. It’s just something to be aware of. Tire temperatures: Every adjustment made on a race car, the goal is to maximize the grip of each tire. Taking tire temperatures after the car has had 8 to 10 hard, competitive laps will tell more positive facts about how the chassis is handling than anything else. Reading tire temperatures is one of the methods in chassis tuning where it is possible to get away from guessing methods and work with predictable variables. Comparing tire temperatures across the surface of the LF and RF tires it can be determined if each wheel has the proper camber angles, proper toe, proper weight distribution, as well as proper tire inflation. By reading the average temperature of the RF and comparing it to the average temperature of the RR we can tell if the chassis is loose or tight. Comparing diagonal averages indicate the proper amount of wedge in the chassis. The optimal tire temperatures should be in a range of 100 to 140 degrees. Keep in mind that the hotter the tire the quicker it will wear out. It’s also important to know what the outside and inside temperature of each tire is. On a short track it is normal for the inside edge of the RF tire and the outside edge of the LF to be 5 to 10 degrees hotter. On a larger track with longer straights, this spread will be even less. On an oval, the RF tire will have more negative camber, thus resulting in the inside edge of the tire contacting the track more than the outside edge giving you the higher temperature. On the LF you will run with more positive camber, so just the opposite holds true. While cornering these temperatures should even out if you have the correct amounts of camber and or weight transfer. The more camber you run, the higher these spreads will be. On a small track were you spend a lot of time cornering, you’ll find the spread higher. This is because your spending more time cornering than on the straights. If you try to achieve even temps across the tire you may develop a push. This is telling you that you have too much positive camber. Just be sure to check the tire temperatures in the corners. Comparing the average temperature of all four tires will tell you which corner of the chassis is working the hardest. To figure the average temperature of a tire, add the 3 temps across the tire and divide by three. If your RF is a lot hotter than the other three tires your probably pushing because the RF is doing too much work. Work on cooling that tire, by lowering the RF spring and allow the other tires to share some of the load. When a tire is under worked, it’s temperature is a lot lower than the other three tires. Concentrate on that corner of the car, by adding weight to that corner, you increase the temperature of that tire. If a tire is a lot hotter than the other 3 work on cooling that tire. Loose or tight chassis? Compare the RF average to the RR average. The RR should be about 10 degrees cooler than the RF. As the average temperatures approach the same number the car becomes loose. When the RF is greater than 10 degrees warmer than the RR the car will push. Wedge? Check the average of the RF & LR tires and compare them to the average of the two front tires, then to the average of the two right side tires. The diagonal average should be 5 to 10 degrees cooler than both the front and right side averages. Warmer you have too much cross weight. Cooler you need more wedge. Toe-out setting? Compare the inside edge of the RF and the outside edge of the LF. If you have too much toe-out, the tires will heat up more in these two areas. The best way to decipher tire temperatures is to run 10 laps on a particular setup and monitor tire temperatures. Don’t expect to learn everything reading the temperatures only once. It will take a number of 10 laps sessions to sort out everything that is going on with the tires. When analyzing tire temperatures it should be done in a specific order. This is because a problem in one area may mask a problem in another area. Here is what to do: Run 10 laps, adjust front cambers. Run another 10 laps. Adjust tire psi. Run 10 more laps. Adjust toe if needed. Again run 10 laps. Adjust wedge. Run 10 laps. Adjust for tight or loose condition based on RF and RR average. Run 10 laps. Look for overheated or overworked tire. Adjust on that corner. Run 10 laps. Repeat the process all over again. Run 10 more laps. Oh no, I hear you say. This is going to take ages to get sorted out. Yes, it will. But if you want to do it properly, then this is the only way to get it sorted out. When checking tire temperatures it is important to make sure your not locking up the brakes or making any sudden changes in your steering outputs. These will all create erroneous tire temperatures readings. Let’s try to simplify how to read tire temperatures by giving you this guideline. Too much NEGATIVE camber, shows higher temperature on the INSIDE edge. Too much POSITIVE camber, shows higher temperature on the OUTSIDE edge. OVER inflated has higher MIDDLE temperature than the inside and outside edges. UNDER inflated will have a LOWER MIDDLE temperature than the inside and outside edges. Too much TOE-OUT, shows higher temperatures on the INSIDE RF and OUTSIDE LF edges. Too much TOE-IN, shows higher temperatures on the OUTSIDE RF and INSIDE LF edges. TIGHT condition when RF is more than 10 degrees HOTTER than RR. LOOSE condition when RF is more than 10 degrees COOLER than RR. HIGHEST average temperature is the corner that is being worked the MOST. LOWEST average temperature is the corner that is being worked the LEAST. LESS WEDGE when RF and LR diagonal average is the SAME or HIGHER than the front and right side average. MORE WEDGE when RF and LR diagonal average is more than 10 degrees LOWER than the front and right side average. Lets look at some examples: (The I M O reading is the Inner, Middle and Outer section of the tire) RF RF RF RF RF RR RF RR RF RR As you can see from the above example there isn’t always an immediate cure. Chassis setup is sometimes like solving a very complicated puzzle. Experiment and learn as you test. Always keep in mind that you may be going the correct way, but there could be an adjustment elsewhere that may be masking your initial change. Because of this chassis setup can become very frustrating for the novice and experienced alike. For every change you believe your
making for the better, it will have an adverse effect elsewhere in the chassis.
If for example your car feels great going into and through the middle of a
corner, but is loose on exit, you have to tighten it up somehow. Curing the
loose condition exiting the corner now has probably messed up your chassis
going into the turn. Now you must loosen it up again. It’s a constant battle of
give and take. By monitoring tire temperatures you can eliminate some of the
mystery of how and why a chassis is reacting like it does. Thanks for visiting our site, FMI Racing
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