This is positive caster. The...
This is positive caster. The top ball joint center is behind the lower ball joint center.
Negative camber leans the...
Negative camber leans the top of the tire toward the center of the car.
These shop tools are used...
These shop tools are used to check caster angles. The tool on the left is for GM metric frame spindles. The notched tube is 41/16 inches overall in length and has a 1/2-inch inside diameter. The tool on the right is for Chevelle spindles. Its tube is 51/2 inches long with a 1/2-inch inside diameter. These measurements may vary slightly with different ball joints. The welded-on rod is 15 inches long. It must be square to the tube after welding.
The metric frame caster tool...
The metric frame caster tool is attached to Brad Doherty's UMP Modified spindle. The angle finder reads caster directly, whether the wheel is exactly straight or not.
The caster tool also works...
The caster tool also works as a camber tool. The 15 inch rod fits against the inner lip of the wheel in a vertical position. Notice that it does not need to be centered on the wheel. The angle finder reads camber directly.
A pair of these tools is used...
A pair of these tools is used for setting the toe. They can be made from whatever material is handy. Sleepys are made from 3/8-inch rod. The short bar is 10 inches long, the center is 15 inches and the long bar is 30 inches.
Toe setting measures whether...
Toe setting measures whether the tires point away from or toward each other.
In the world of race car setup, the frontend settings can become downright confusing. But theres much to gain by understanding caster, camber and toe settings, and how they can work together to make your race car go faster.
A side view of the car shows an imaginary line runs through the center of the upper ball joint to the center of the lower ball joint. This is known as the pivot line. If this line is absolutely vertical, then the caster measurement is zero, or no caster. When the top of this line is leaned toward the rear of the car, we now have positive caster.
Try pushing around a chair with casters on it. You will find it has no directional stability. This is because the casters have negative caster and want to follow the slightest force in any direction. Your race car should have
positive caster to achieve that directional feel.
As opposed to some years ago, most race cars now have power steering. This allows the use of more caster.
In cars using stock or near-stock frontend geometry, caster can be increased from the factory settings. Caster stagger is also a useful setting. Caster stagger occurs when there is more positive caster on the right side than on the left. When entering a turn to the left, the excess caster on the right will give the car a natural tendency to turn left.
Long tracks, especially the paved ones, need only a small amount of caster staggerperhaps only 1 degree. At a ¼-mile dirt bullring, much more can be an advantage. The IMCA stock car we recently put together in Stock Car Racing uses 9 degrees of caster on the right and 5 degrees on the left. This is a lot, but the car turns in easily.
Setting caster is easily done with a gauge built for that purpose. Most of the store-bought units screw on or magnetize to the front hub. Turn plates are then placed under the front wheels. The wheels are steered a certain number of degrees each way. The gauge will then read the caster in degrees. This type of gauge may be necessary with aftermarket rod ends.
We have constructed a simple gauge for use with stock ball joints. Each gauge will fit only the type of car it was made for. Notice each ball joint has some threads sticking out past the nut. Find a piece of tubing that will fit snugly over the ends of the ball joint tang. Measure the distance between the nuts on the top and bottom. Cut the tubing about 1/16-inch shorter. On one end, notch the tubing ½ inch down and halfway across. This will leave a half-round notch. Weld a 15-inch rod at a 90 degree angle to the tube on the notched side. The tube should be 11 inches from the end of the rod. After welding, make sure the rod is at a 90-degree angle to the tube.
Now place the tube over the bottom ball joint threads. The notch will allow the inside of the tube to rest against the upper threads. Place an angle finder on the rod and directly read caster.
Lots of caster stagger is ideal on a small dirt track. Get all the caster the right side will allow with the correct amount of camber. Then adjust the left-side caster using enough caster stagger to give you the feel you want entering a turn. Start with a lot and then take it out if you dont like it.
Another setting for the front suspension is camber. Camber is measured at the wheel, not the ball joints. A frontal view of the car, when the wheel is straight up (no lean), shows the wheel has no camber. When the wheel is leaned in at the top toward the center of the car, it has negative camber. Therefore, when it leans out at the top, the wheel has positive camber. Race cars can use both positive and negative camber settings to their advantage.
Camber is a very visible part of the frontend settings. We have all seen the right front leaning toward the center of the car. Sometimes this is severe enough that the outside of the tread is not touching the ground. This much negative camber reduces the traction at the front of the car. If the car seems balanced in its handling with this setup, then the suspension is crippled somewhere else.
Only the right amount of camber will net maximum traction. Selecting the right amount is determined by the built-in suspension design. All the suspensions we deal with have camber gain. When the wheel goes up in relation to the chassis, which is called bump travel, the camber increases, or gains. Camber is designed to reduce the effect of tire flex. Camber gain also adjusts for suspension movement. Together, they work to keep the tread surface flat on the track. The big question is how much do you need.
The tire needs about 1 degree to start with. With most suspensions discussed here, there will be a gain of 1½ degrees to 2 degrees per inch of bump travel. If your suspension has 3 inches of bump travel, that would add up to 4½ degrees to 6 degrees. Add in the 1 degree negative initial setting and you have 5½ to 7 degrees negative at full travel.
This is best accomplished by blocking the chassis and removing the spring. Then the suspension can be cycled with a jack. Set the camber at full bump travel. The car should be level. Then with the spring replaced and the car on its wheels, measure the camber. From now on that will be your static camber setting on the right front.
A problem with some stock suspension mountings is not allowing all the caster needed while providing enough camber. Split the settings, if necessary, by removing a degree of caster and a degree of camber. Just keep the caster stagger the same.
Camber on the left front will not be the same as on the right. You will need positive camber on the left front wheel. There is little camber change as the left front goes down, the reverse of bump travel. Therefore, an initial setting of ½ to 1 degree positive camber will work well.
Camber can be set using store-bought gauges or with the homemade caster gauge described above. Earlier the rod was cut to 15 inches. This length allows you to fit the rod to the wheel and use the angle finder to measure the camber. An angle finder with a magnetic attachment definitely makes reading easier.
When setting up the car, its often not desirable to have the front wheels exactly parallel to each other. Some situations call for toe-out while others call for toe-in, thus the term toe setting.
The toe setting will vary with the type of track and the steering linkage. Long tracks and/or paved tracks may require toe-in at times. Most of our cars with stock-type steering linkages running the small dirt tracks will need a bit of toe-out to work properly. This is not a case of if somes good then mores better. A toe-out of ¼ inch to 3/8 inch is about right for most. Too much adds drag. Too little will give the car an unstable feeling.
Toe is best measured some other way than hooking a steel tape in the tire tread on one side and going to the other side. The tire tread is notoriously less than straight on the tire carcass. When two people hold a tape across the tires, it is very difficult to keep the measured points the same distance from the ground. When the measuring points are not the same height on the tire, the distance between them changes. Instant error.
Toe boards are available that have saw slots in which to hook two steel tapes. These lay against the tire on each side of the car. They work OK when the tire has no bulges or raised letters.
We have made toe setting tools which key off the wheel. They may be more accurate as long as the wheel is straight. They are made of 3/8-inch steel rod and welded together. The top crosspiece is 10 inches long, the center bar is 15 inches and the long bottom bar is 28 inches. There is no slot to hang the tape, just line it up with an edge. This aids accuracy by not letting a pull on the tape move the tool.
Lay two steel tapes next to the ends of the bottom rods. Make sure each reads the same on the hook end. Read the toe-in/out on the other.