Thoughts On Toe, Caster & Thrust Angle

[danbyrambler]

Saw this on TRUCK U - - - Not about price - Worth it or not - Just their slant on HOW TO - - Mostly for racers but anyway,

 

 http://www.quicktrickalignment.com/

 

Some of their Info/How to:

 

 

 How to Set Toe Properly:

 

You will get better more consistent results adjusting your toe in settings if you go the extra mile to eliminate variables.

 

Before you begin taking measurements, you must insure that the car is ready. Ride heights set, camber and caster set, Ackerman set, air pressure set, stagger correct….you get the idea. You should also inspect the steering components and replace any that are worn or bent. Center up the steering before you begin. Center the drag link or rack so that the inner control pivots and inner tie rods are centered to each other. Tie rod lengths should be adjusted to match you lower control points if possible.

 

String the right side of the car to line up the right front to the right rear. By lining up the right side and starting with the right front in line with the right rear you will eliminate any Ackerman effect that is in the car. If the wheels are turned away from straight when you take your toe measurement the Ackerman effect can add toe out that will not be present when the wheels are straight ahead. Take the time to string the right side and you will get more precise results. Make sure to settle the car and roll it forward just before taking a reading. By rolling forward the caster in the car will pull the front wheels and take any clearance in your suspension components all in one direction. Be sure not to let the car roll back after you have rolled it forward. By rolling the car forward each time you will get more accurate repeatable results. Be sure to roll the car back then forward after each adjustment to relieve any pressure in the tire and suspension components.

 

When taking toe measurements that utilize the side wall it is always a good idea to spin each front tire and mark the high spots on the side wall with a piece of chalk. Jack up the car and spin the RF wheel. Hold a piece of chalk on a jack stand about 1/8″ away from the sidewall. Spin the tire and see if the chalk hits anywhere on the sidewall. If the chalk does not leave a mark then move the chalk gradually closer until you get marks on the high spots. Then find the uniform spots on the side wall and orient the tire so that those points will touch the QT stick when the car is on the ground. Lower the car and repeat the process on the other side.

 

Almost all racers know the difference between toe-in and toe-out when dealing with alignments. However, the many forms of toe can be confusing or misunderstood. Toe-out or toe in can be found in at least one of five main forms:

 

Static. The most commonly known form of toe-out is “static” toe-out. This is where the tie rods are adjusted such that the front tread of the tires to be farther apart than the rear edges of the tires.

 

Ackerman Steering. “Ackerman” is designed into the steering geometry. This causes the wheels to toe-out when the steering wheel is turned. This is why some shops and dealerships refer to Ackerman as “toe-out on turns” (and is not to be confused with static toe-out).

 

Bump steer. The toe-out in this situation occurs during ride motions or body roll. Often the factory will use this to improve transient dynamic handling on production cars.

 

Steering arm. This is a popular trick with round track racers; it is created by having a shorter steering arm on the left spindle than on the right spindle. When the steering wheel is turned to the left, the left wheel is steered a larger number of degrees than the right wheel resulting in toe-out. However, if you turn to the right the wheels toe-in.

 

Slip angle. This is an unusual form of toe-out and can occur at the tire’s contact patch rather than at the wheel. Because the outer edge of the tire in a corner is more heavily loaded than the inside , the outside of the tire will run at a larger slip angle than the inside (despite the name “slip angle,” it has nothing to do with slip but rather the twisting of the  contact patch in relation to the wheel). This additional twist in the outside contact patch can result in the contact patches being toed-out.

 

CASTER:

 

Caster controls how well the car turns. If you are looking at your car from the side, caster is the angle of an imaginary line between the upper and lower ball joints relative to vertical. If that line is angled so that the top leans toward the back of the car, that’s positive caster. If the top of the line leans toward the front of the car, that’s negative caster. Positive caster makes the car feel more stable and resists turning. If you are turning a car that has positive caster on both front wheels and you let go of the steering wheel, it will automatically straighten up. Negative caster does the opposite and usually makes the car feel darty. Racers rarely run negative caster.

 

THRUST ANGLE:

 

I missed it if they covered this important part of alignment - - TA should be zero - If not your ride will pull/veer towards the short side during acceleration/power & the other way during deceleration/coasting

 

:smart: