Diagnosing Tire Wear

Tire wear is a dead giveaway that the wheels are out of alignment or that steering or suspension parts are worn. So anytime you find unusual tire wear, be sure to give the steering and suspension a thorough inspection to find out what's causing the problem.

Diagnosing Tire Wear

Toe wear -
A feathered wear pattern across both front tires, and sometimes shoulder wear on the inner or outer edge of both tires. Toe wear is usually caused by worn tie rod ends, but may also result from worn or loose inner tie rod sockets on rack and pinion steering gears. Other causes include bent steering arms or misalignment in the rear wheels. Measuring toe out with the wheels turned 20 degrees to either side can help you detect a bent steering arm.If toe wear is accompanied by steering looseness or steering wander, there's a very good chance the tie rod ends are worn. Proceed to the steering checks. If toe wear is accompanied by steering pull or off-center steering, rear wheel toe alignment or axle alignment may be out of specifications.

Camber wear -
Uneven wear on one side of a tire may show up when control arm bushings have collapsed, ball joints are loose, a spindle or strut is bent, or a strut tower is out of its normal position (due to factory misassembly, collision damage, body sag or severe corrosion).Another overlooked cause of camber wear can be a front-wheel drive engine cradle that has shifted out-of-position to one side. A weak or broken spring can also allow camber changes in the suspension that produce camber wear on a tire.

Cupped wear -
This may be the result of badly worn shocks or struts, or wheel and tire imbalance.

Measuring Tire Wear-
Tires have wear bars (flat spots)in the tread grooves to visually indicate wear. If the tread is worn down so the wear bars are flush with the surrounding tread, the tire is worn out and needs to be replaced. If you see cords showing through the rubber, the tire is unsafe to drive on and is on the verge of failure. Replace the tire without delay! The same advice goes for any tire that has bulges, deep cracks or the tread is separating from the casing. Tread wear can be measured using a penny. Place the penny with Lincoln's head upside down in a groove between the treads. If you can't see the top of Lincoln's lead, the tire is okay and still has some wear left in it. But if the top of Lincoln's head is flush with the tread, the tread depth is 2/32-inch (1.6mm) or less, indicating the tire is worn out and needs to be replaced.
Some experts now say the same test should now be done with a quarter. If the top of Washington's head is flush with the tread when you place a quarter upside down in a groove, the tread depth is 4/32-inch (3.2mm). Though the tire still has some tread wear left, braking, traction and handling are significantly reduced compared to a tire with more tread on it. Because of this, many experts now recommend replacing tires when the tread depth is worn down to 4/32-inch or less.

Check Ride Height-
When tires show rapid or unusual wear, alignment problems caused by worn or bent steering or suspension parts is always a possibility. Ride height is something that should always be measured when troubleshooting suspension problems. Coil and leaf springs invariably sag with age, which can alter camber as well as caster alignment. The constant load that bears down on a spring eventually causes the metal to creep. Measuring ride height will tell you if the springs are still within specifications or not.

Notice I said measure. That doesn't mean take a quick glance and let it go at that. It is hard to see small but significant differences in ride height side-to-side, and virtually impossible to tell if a vehicle is within the factory specified ride height dimensions without using some type of measuring device.

If ride height is below specifications, the springs are weak and replacement should be recommended.

If ride height is okay but camber is out of specifications and a tire shows heavy shoulder wear, measuring the Steering Axis Inclination (SAI) angle and Included Angle can help you determine if something is bent or out of position.

A strut tower that's leaning in or out will affect camber alignment and give you an SAI reading that's greater or less than specifications. If the strut tower is pushed back or pulled forward, it will upset caster but SAI will be okay.

A bent spindle can affect either camber or caster or both depending on which way its bent. Also, don't forget to check the control arms and control arm bushings. A bent arm and/or collapsed bushing can also cause changes in camber and caster.

Steering Checks -
The steering can be inspected one of several ways. A test drive will often reveal problems that may escape detection in the service bay. Things like steering effort, return, stability, feel and noise are impossible to check without actually driving a vehicle. So if possible, take a short test drive and note of how the steering feels and responds.

Another way to check the steering is to do a "dry park" check. With the full weight of the vehicle on the wheels, have a helper rock the steering wheel while you look for play or looseness in the steering linkage and steering column. On some vehicles, this can be done by reaching up and rocking the steering column coupling from underneath while the vehicle is sitting on a drive-on ramp-style lift. The dry park method of checking for looseness is generally the best procedure to use because the weight of the vehicle on the wheels creates resistance that makes it easier to see play.

The dry park method is also a good way to find loose upper strut bearing assemblies. While rocking the steering back and forth, watch for strut movement in the strut tower opening. Any wobble would tell you the strut bearing plate is worn and needs to be replaced.

Something else to check is the geometry of the steering rack and tie rods. If the rack and/or tie rods are not parallel to the road, it can create a "bump steer" condition. Bump steer is when the vehicle suddenly darts to one side when crossing over a bump or dip in the road. The steering pull is caused by uneven toe changes that occur as the suspension bounces up and down.

The cure here is to reposition the rack so it is parallel to the road - loosen and retighten the rack mounts, if possible- or replace the steering knuckle if an arm is bent

Worn Tie Rod Ends-
Toe wear is often due to worn tie rod ends. A bent tie rod or steering arm can also change toe, but in most cases the culprit will be worn tie rod ends. As a rule, tie rod ends should show no visible vertical or horizontal play when rocking the steering back and forth with the full weight of the vehicle on its wheels.

The inner tie rod sockets on rack and pinion steering gears are enclosed in bellows, making them difficult to inspect. If the bellows are rubber, you can check for looseness by squeezing the bellows and pinching each socket while pushing outward on the wheel or while a helper rocks the steering wheel. If you feel movement, the sockets are loose and need to be replaced.

You can't do this check with hard plastic bellows, so lock the steering wheel with a holder and watch for any in or out movement in the tie rod while pulling and pushing on the wheels. Also pay attention to the rack mounts. Loose, deteriorated or broken mounts may allow the rack housing to move as the wheels are steered. This can cause steering wander and noise.

With parallelogram steering systems, pay close attention to the amount of play in the idler arm. Looseness here can cause steering wander and toe wear. Pitman arms should show no vertical looseness. Center links should be like tie rod ends and show no vertical or horizontal looseness.