What Is Caster – Camber – Tow-in – Wheel Alignment
First for those who do not understand caster, camber, and tow-in let me explain. Caster is how the wheel is in relation to a vertical king pin or ball joints. It can be true vertical or -o- degree, positive, or negative. Example: the front wheel of a bicycle has positive caster. Note the wheel extends forward from the turning axis. Therefore allowing the steering to return straight when you remove your hands from the handle bars. A vehicle with positive caster will do the same. This adjustment is for handling or how it drives and requires caster – camber gauge for adjustment as well as certain hand wrenches.
Camber denotes the position of the wheel to the vehicle, such as in at the top and out at the bottom (negative), or out at top and in at the bottom (positive). The recommended setting can be negative 1 to positive 1, -0-degree being straight up and down, or true vertical. If it is extreme one way or the other it will cause wear on the inter or outer edge of the tire and possible scallops may appear. This adjustment is for tire wear and possibly some handling, also certain tools such as upper control arm wrench and a tomcat camber adjustment tool may come in handy.
After the caster and camber are set, we go to the tow-in which is also for tire wear and again possibly some handling. Tow-in is the adjustment relationship of the left front wheel to the right front wheel. If the tires of the front wheels are slightly pointed toward each other, that is tow-in. If they are away from each other that is tow-out. Before this adjustment takes place, the center of steering must be made. This is the relationship of the steering wheel to the left front wheel, With the steering wheel set straight ahead (centered) align the left wheel towed -in slightly or about 3/16 in. This can be done by with the use of a string drawn from the around the left rear wheel and pulled forward using the rear wheel as a guide to get a straight line to the left front wheel therefore allowing the string will indicate the position of the left front wheel being tow-out or tow-in. The left wheel must be adjusted first and the right ft. wheel adjusted to the left wheel to get a toe-in of about 1/4 in. There are tow-in adjusting tools such as tow-in adjustment bar, a tie rod spreader, and tie rod kit, that can aide in accomplishing this alignment.
There are times when one shim or adjustment to move the rear of the control arm outward will give a wheel the proper setting if one understands what that move will do for both settings (caster and camber) simultaneously. That knowledge or understanding plus the proper hand tools and some experience is all that is really needed. Well, maybe a good coach would come in handy. However, back to the move made by the adding a single shim to the rear of the upper control arm (by the way shims vary in thickness) would give less negative caster and more positive camber. I hope this helps! Any questions? Lem Boyd