rear of the front wheels, as shown in figure 12-5. Note that line B is shorter than line A. The setting is taken at spindle height with the wheels in the straight-ahead position. Toe-in is measured in fractions of an inch. It is a tire wearing angle. The purpose of toe is to compensate for the normal looseness required in the steering linkage and to balance the effect of camber on the tires. The natural tendency of the wheel is to rotate like a cone around the point. If both front wheels are forced to follow a straight path by the motion of the vehicle, there is a continual tendency for the tires to slip away from each other. Toed-in wheels tend to travel toward each other and counteract this condition. By properly relating camber and toe-in, tire wear is reduced to a minimum. The motion of the wheel is balanced between two opposing forces, and pull on the steering mechanism is reduced.

Of all the alignment factors, toe-in is the most critical. A bent tie rod will change the amount of toe. Toe-in is adjusted last by your turning the tie rod sleeves.

5. TURNING RADIUS. The front-end assembly of the modern motor vehicle requires careful design and adjustment because each front wheel is pivoted separately on a steering knuckle. Because of this construction, the front wheels are not in the same radius line (drawn from the center of rotation [fig. 12-6]) when a vehicle is making a turn. Because each wheel should beat right angles to its radius line, it is necessary for the front wheels to assume a toed-out position when rounding curves. If they do not, the tires slip, which causes excessive tire wear. The inner wheel (the one closer to the center of rotation) turns more than the outer wheel, so it will travel in a smaller radius. This difference in the turning ratios of the two wheels is called toe-out. It is usually specified as the number of degrees over 20 that the inner wheel is turned when the outer wheel is turned 20 degrees. The-out on turns may be checked, but there is no provision made for its adjustment. The steering linkage must be examined carefully for bent or defective parts if this angle is not within the manufacturer's specifications.

6. TRACKING. Tracking (fig. 12-7) is the ability of the vehicle to maintain a right angle between the center line of the vehicle and both the front and rear axles or spindles. (The rear wheels should follow the front wheels.) If this angle is off, the vehicle will appear to be going sideways down a straight road. This problem could be caused by shifted or broken leaf springs or a bent or broken rear axle mount, bent frame, bent steering linkage, or misadjusted front-end alignment.

Figure 12-7. - Rear wheels must track correctly.

ADJUSTING WHEEL ALIGNMENT

In the preceding paragraphs, we covered the principles of the different angles involved in front-end alignment. In the following paragraphs, we will cover safety, tools, and alignment procedures.

SAFETY PRECAUTIONS

You should keep the following precautions in mind when you are working under a vehicle:

1. While repairing or adjusting the steering system and the wheel alignment, be sure the vehicle is and will remain stationary. At least one wheel should be blocked on both sides, even if the equipment is on a level surface.

2. Make yourself familiar with a suspension system before you work on it; know the "jack" points. You need to know which components bear the weight of the vehicle.

3. Make use of jack stands!

4. When using alignment equipment, follow the manufacturer's instructions.