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.

• 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).

• 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.

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.

Power Steering Checks
Steering effort on both manual and power steering systems should be checked during the test drive or in the service bay with the weight of the vehicle on the wheels. Unusually high effort combined with poor steering return may indicate binding in the steering rack or improper yoke adjustment. Other causes can include binding in tie rod ends, ball joints or upper strut bearing assemblies.

Power steering can also be checked with the wheels off the ground. If the steering wants to turn to one side when the engine is running, it indicates a problem in the control valve.

Don't forget to check the fluid level in the power steering pump reservoir, too. A low level may indicate leakage. A visual check of the pump, hoses and steering gear should reveal the source of any leaks.

Some hissing noise is normal with most power steering systems, but excessive noise may indicate a bad check valve. Belt squeal would tell you the belt needs to be tightened or replaced. Pump noise usually indicates wear.

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 play.

Don't Miss Ball Joints
Worn ball joints can also effect wheel alignment, but the greatest danger is the suspension collapsing if a worn or loose ball joint separates or pulls apart. Worn ball joints are usually noise on rough roads producing a clunking noise when passing over bumps.

If the ball joints have built-in wear indicators, joint play should be checked with the weight of the vehicle on the wheels. Ball joints without built-in wear indicators are generally checked by raising the suspension to take the weight off of the joints. But procedures vary.

On rear-wheel drive applications with SLA suspensions where the spring is on the lower control arm, modified strut suspensions which also have the spring on the lower control arm, and front-wheel drive wishbone strut suspensions where the spring is on the strut but the strut is connected to the lower control arm, the lower ball joints carry the weight and must be unloaded to measure play.

This is done by raising the vehicle and supporting the lower control arms to take the weight off the lower ball joints, then pulling on or prying against the wheel (not the ball joint) to measure vertical and horizontal play in both the lower and upper ball joints. Also, it's important to make sure the ball joint is securely attached to the control arm by looking for any signs of movement between the ball joint housing and arm.

If an SLA suspension has the coil spring over the top arm, the upper joints are loaded. To check these joints, the vehicle has to be raised and the upper control arms blocked or supported to unload the upper joints.

With MacPherson struts, the strut supports the load so the lower ball joints are unloaded. To measure play, simply raise the vehicle and allow the suspension to hang free. Then push on or pry against the wheel to measure vertical and horizontal play in the lower ball joints.

To check rear ball joints on a front-wheel drive car with an independent rear suspension, raising the wheels and supporting the suspension arms will unload the joints. Note: All ball joints should be checked prior to lubricating the chassis (if joints are greaseable) because grease may temporarily take up slack in the joint.

The amount of horizontal (radial) and vertical (axial) play that is allowed in a ball joint will vary depending on the joint type, location and vehicle application. Always refer to the vehicle manufacturer's specifications, and use a dial indicator to measure the amount of play unless the joint is obviously shot.

Inspect Other Hardware
Front control arms as well as rear trailing arms and lateral links should all be visually inspected for damage or cracks. Also, make sure the ball joint is securely attached to the arm.

Check the bushings for excessive movement, deterioration, cracking or crush. This can be done by gently prying against the control arm to see if the bushings allow much movement. A little "give" with rubber and elastomer bushings is normal, but if you see more than about 1/8 inch it may mean the bushing has collapsed. Metal bushings should have little or no play. Bouncing the suspension can help you identify noisy bushings.

On sway bars, check the sway bar bushings and mountings. The mountings should be securely attached to the chassis, and the bushings should be in good condition with no cracks, splits, crushing, etc. Check the end links of the sway bar and their bushings, too, for looseness. If the ends of the sway bar are attached directly to the control arms, check to see that the mounting is secure.

Bearing the Problem
Loose wheel bearings can cause steering wander while worn bearings typically produce noise. To check the bearings, raise the wheels off the ground and spin each wheel by hand to check for roughness or noise in the bearings. Do not confuse normal brake drag for bearing noise. If the bearings are rumbling or clicking, removal for cleaning and further inspection will be necessary - unless the bearings are the sealed variety, in which case replacement would be required.

To check wheel bearing play, grasp the wheel at the top and bottom, then try to rock it back and forth by pushing in with one hand while simultaneously pulling outward with the other hand. Alternate back and forth to see if the wheel rocks or moves. If you feel movement, the bearings are loose. Refer to specifications for the maximum allowable play.

Serviceable wheel bearings can be readjusted to reduce play by removing the dust cover over the hub nut, removing the cotter pin that secures the hub nut, and then tightening the nut according to the vehicle manufacturers specifications to set preload. Sealed wheel bearings are not adjustable. If play exceeds specifications, the bearing assembly must be replaced.

Don't Just Bounce
A rough ride, bottoming, excessive swaying when cornering, etc. are classic symptoms of worn shocks and struts.

A simple "bounce test" will usually reveal shocks that are badly worn, but a test drive will give you a more accurate picture of their condition. If the dampers are doing a poor job of controlling spring rebound and body motions, it's time for a new set of shocks and/or struts.

When visually inspecting the shocks and struts, look for:

• Physical damage (broken mountings, bent rods, etc.).
• Fluid leakage (which indicates seal failure).
• Loose, collapsed or cracked rubber mounting bushings.
• Physical contact with other suspension components, exhaust pipes or brake lines.
• Any of the above conditions would call for repairs or replacing the bad shocks or struts.

Proper torque on lug nuts is very important for three reasons. One is to keep the lug nuts from loosening up and the wheel coming loose, another is to prevent distortion of the brake rotor behind the wheel, and a third is to prevent broken studs. A torque wrench should be used for final tightening of the lug nuts, and the nuts should always be torqued to the recommended specifications.

CAUTION: Torque specifications for lug nuts are always for CLEAN and DRY studs and lug nuts. That means no oil, no grease, no anti-seize and no lubricants of any kind. Any of these products will reduce the friction between the threads. This may seem like a good thing to prevent rust and frozen lug nuts, but the reduction in friction means a much higher percentage of the applied torque (up to 25% or more) will go toward loading the lug nuts. The end result may be brake rotor distortion or broken studs!

Wheel studs should be cleaned with a wire brush to remove rust and dirt BEFORE the wheels are mounted. If the lug nuts are heavily rusted or have damaged threads and won't turn easily on the studs, replace the lug nuts. The same goes for any wheel studs with damaged or badly corroded threads. And remember to mount the wheels DRY with nothing on the threads.