Modern suspension systems offer certain adjustments to allow for such variables as manufacturing tolerances, wear, changes in tires, and even accidents. But wherever there’s an adjustment it’s possible for parts to wear over time or to slip a little bit (particularly when bumped hard), resulting in misalignment. Also, any time something related to the suspension changes, as when a new set of tires are installed, alignment can change as a result. Periodically checking and adjusting the alignment is a necessary part of keeping every vehicle running safely and economically.

• Toe: While tires should face almost directly forward, sometimes slight deviations from that are used to help the vehicle track straight even on rough or crowned roads; these deviations from straight forward are called toe. Excessive toe (inward or outward) dramatically increases tire wear and can decrease fuel economy because the tires rub against the road instead of merely rolling, and large deviations from proper toe settings can make a vehicle difficult to control.

• Camber: The extent to which tires are tilted toward or away from the center of the vehicle, when viewed from the front or rear, is called camber. If the tires are exactly vertical (0° of camber) then acceleration and braking performance are maximized, while a slight tilt of the tops of the tires toward the inside (called negative camber) can help handling because it compensates for the forces incurred during cornering. When camber is even a little bit too great (positive or negative), tire wear increases greatly because one edge of the tire takes all the load; when camber is badly misadjusted, safety becomes an issue as braking performance suffers.

• Caster: Caster, which is usually adjustable only on the front tires, is the difference between where a tire touches the road and the point at which it pivots when turned. Picture the front wheels of a shopping cart, which automatically align themselves when the vehicle is pushed forward, to understand why this can be important. Correct caster settings help the vehicle track straight; incorrect settings can make the vehicle unstable or difficult to turn.