Miss part I? Click here
Good friends of mine, Ben and Claire, noticed some unusual wear on their front tires. They were leaving the city for a few days, a monthly ritual to escape their busy lifestyles, and had bumped a curb parking. Innocent enough and something that could happen to anyone. ...
In Part I of our article we looked at the signs of misalignment and the possible causes. In this part II we'll look at the specifics of the alignment process.
Several measurements are checked during an alignment. The things the mechanic needs to look at are camber, castor and toe.
This is the angle of the wheels. You might have seen race cars where the top of the wheels angle in towards the car, this is called negative camber. If the top of the wheel angles away from the car, it's called positive camber. Camber is the inward or outward tilt of the wheels and keeps the tire flat on the ground during a turn.
If the camber setting for your vehicle isn't correct it will cause poor handling and wear your tires prematurely. Too much positive camber and the tires wear on the outside. Too much negative and they will wear on the inside. If the camber settings are not the same for both wheels your vehicle will pull to one side.
Caster refers to the angle of the wheel in relation to the steering connection. A high caster angle will give you greater stability at high speeds, but the compromise is your steering may be difficult at low speeds — Just the ticket if you're a race car driver.
On the other hand, a lower caster angle will give you easier steering at low speeds. However, the compromise is the vehicle may wander at higher speeds.
For most cars it's most practical to have a caster that's somewhere in the middle of these two extremes. This will achieve good all-round stability and control at both high and low speeds. Properly adjusted caster allows the wheels to track in a straight line and prevents shimmy. Take a look at the shopping cart caster angle as shown in the figure above.
When you push a shopping cart equipped with caster wheels, it tends to roll in a straight line because the wheels trail behind. The greater the trailing distance, the greater the tendency to roll straight. The caster setting on a vehicle is adjustable to increase or decrease the effective trail distance.
Toe is exactly the way it sounds.
Toe-in is when two wheels on the same axle are angled slightly inward. They will be closer together at the toe than the heel ends — just like if you looked down at your feet and pointed your toes in.
Toe-out is the opposite, the two wheels are angled slightly outward, just like if you positioned your own toes out. Severe toe-in or toe-out can cause uneven and excessive wear so one side of the tread wears out more quickly than the other.
The Toe settings on your vehicle affect the handling when you turn. Toe-in causes understeer and may make the vehicle feel like the back end is trying to come around to the front when you take a corner. Toe-out causes oversteer and makes the vehicle feel like it is "diving" into the turn too sharply.
Too much toe-in will wear the tread off the outside edges of your new tires. Too much toe-out will wear the inside. This type of wear is called feathering and can be detected by running your fingers across the tread of the tire.
Every vehicle has factory specifications for camber, caster and toe which should be followed precisely. Improper alignment not only causes poor handling and premature tread wear, it can also reduce fuel efficiency.
Remember that misalignment can occur because of daily wear and tear from the road surface, particularly potholes and railroad crossings. If you have an accident this could also cause misalignment.
You might want to have your vehicle's alignment checked if:
See more about tire wear here.
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