Understanding the complexities of front-end geometry
Unlike the old days when a good wrench was the best method to set up a race car, today a good grasp of mathematics is more important to understanding the complexities of front-end geometry.
Geometry plays an important role in racing. From how a driver apexes the corners of a track to how his team sets up the front end suspension of his race car. If you don't know how to use geometry to your advantage then you will not be a successful racer.The Oxford American Dictionary defines Geometry as follows: "The branch of mathematics concerned with the properties and relations of points, lines, surfaces and solids. And, the relative arrangement of objects and parts." Sounds simple enough to me. So why is working with geometry one of the most difficult aspects of dealing with a race car? If a race car remained in a static position then it would be simple to calculate the front-end geometry because nothing would move and the "points and lines" of the car's suspension would not change. But, as we know, that is not the case. In a race car we deal with all sorts of moving triangles, parallelograms and trapezoids in the suspension system. Each time one of these "points or lines" moves [or is moved] then their "properties or relationships" to each other change. If you change just one "point" in the equation then you change the relationship of all of the others. That turns a simple geometric equation into a complex calculation that can drive setup specialists and drivers crazy if it is not done correctly. I always found it difficult to calculate the angle of the dangle against the swerve of the curve but today's teams have computers and programs to help them do it. To better understand the complexities of setting up a car's front-end geometry you need to first understand the goal of the setup specialist. His goal is to keep the "tire patch" [the surface of the tire that contacts the track] and the "slip angle" of the tire [the point at which a tire will lose grip and slide across the track] constant and controlled so the driver will be comfortable and confident when he dives into a corner at high speeds.
CamberCamber is the relationship of the tire and wheel to vertical. If the top of the tire leans into the centerline of the car then that is called negative camber. If the top leans away from the centerline then that is called positive camber. Sprint Cup cars usually will run about five degrees of negative camber in the right front and maybe one to two degrees of positive camber on the left front on oval tracks. This helps to compensate and offset for the body roll when the car goes into the corner at high speed and leans toward the outside wall. You want the camber to be enough to keep the tire patch in constant contact with the track in the corners but not so much that it disproportionately wears the inside of the tread off the right front tire [outside tread on the left] when the car is going straight. Logic would therefore tell you that you can run more camber on shorter tracks with shorter straights than on bigger tracks with longer straights. The amount of the banking will also influence how much camber you want to run. Flatter tracks require more camber than higher banked tracks because there is more lateral loading of the tire tread on a flatter track. Tire temperature readings across the surface of the tire will tell the setup specialist when he has achieved the correct balance.
CasterCaster is an important component of the front-end setup. Caster is the relationship of the upper and lower pick-up points to vertical but in the opposite direction of camber. If you manipulate camber east to west then you would manipulate caster north to south. If you move the upper pick-up point forward of the vertical centerline that runs through the two points where the tire, wheel and spindle attach to the arms extending from the frame then you are creating positive caster. Move it back and you create negative caster. So why is it important? Positive caster helps to minimize or redirect the dive [compression] when the car is turned and goes into the corner. On an oval track, positive caster on the right and negative caster on the left will also help the car turn through the corner by having the right tire and wheel "reach" forward while the left tire and wheel will pull back. This is because the inside tire and wheel are traveling on a tighter radius than the outside tire and wheel so you want it to turn more than the outside tire and wheel to avoid scuffing it across the track surface. When you drive your street car in a straight line and let go of the wheel then it will continue in a straight line [or it should[ because the caster is more neutral in your street car's front end. Oval track race cars will go in a circle if you let go of the steering wheel because of the positive caster set into the outside wheel. Oval track race cars are set up to turn left automatically. You have to steer them with the steering wheel and throttle to go straight. Drag cars, by comparison, will run an excessive amount of positive caster on both sides to help the driver to steer the car in a straight line during a drag run.
ToeToe is fairly simple. It is the relationship to parallel of the front tires. Most street cars will be slightly toed in [along with caster] to help them go straight when you let go of the steering wheel. Race cars are slightly toed out to help the car turn into and through the corner. It is the same principle as caster. The inside tire and wheel is making a tighter arc through the corner so toeing the left front tire and wheel out helps the car to turn more easily.
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