Automotive Repair Library, Auto Parts, Accessories, Tools & Equipment, Manuals & Books, Car BLOG, Links, Index
Tire Wear
Copyright AA1Car
.
.
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: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.
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.
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 on wet pavement 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 if you drive in an area that receives a lot of rain or snow.
Worn Tie Rod Ends
The most common cause of rapid tread wear on the front tires is toe misalignment due to worn tir rod ends in the steering linkage. A bent tie rod or steering arm can also change toe alignment, but in most cases the problem is the tie rod ends are worn out and have too much play.
As a rule, inner and outer 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. If you see any movement in the joint, the tie rod end needs to be replaced.
The inner tie rod sockets on rack and pinion steering gears are enclosed in bellows, making them more 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.
Steering Checks
The steering can be inspected using a technique called the "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 ramps or 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.
While rocking the wheel back and forth, also watch the control arm bushings for excessive movement. You can also check the bearings 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.
Underinflated Tires
If the tires are not maintained at the recommended pressure and are underinflated, the tread flexes more than usual as the tire rotates. Over many miles, this will increase tread wear. Check the pressure in each tire with an accurate gauge, and inflate the tires to the pressure recommended in your owners manual or the inflation decal in the glovebox or door pillar.
Sagging Springs or Bent Suspension Parts
Weak, sagging springs can cause a los of ride height that throws off wheel alignment. Coil and leaf springs sag with age, which can alter camber as well as caster alignment. Measuring ride height will tell you if the springs are still within specifications or not.
If ride height is below specifications, the springs need to be shimmed or replaced. If ride height is okay but camber is out of specifications and a tire shows heavy shoulder wear, a strut or steering knuckle may be bent. This type of damage can be found by having the Steering Axis Inclination (SAI) checked on an alignment machine.
A strut tower that is leaning in or out will affect camber alignment and show a SAI reading that is out of specifications. If the strut tower is pushed back or pulled forward, it will upset caster but SAI will still read within specifications.
A bent spindle can affect either camber or caster or both depending on which way its bent. Also, a bent control arm and/or collapsed control arm bushing can upset camber and/or caster.
Worn Ball Joints
Worn ball joints can also effect wheel alignment and cause uneven tire wear. 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.
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, 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 with a dial indicator.
Worn Struts or Shock Absorbers
Tire wear can also be caused by worn struts or shock absorbers. The dampers help keep the tires in contact with the road as it encounters bumps and dips. Wear shocks or struts allow the wheels to bounce too much, which typically results in a cupped wear pattern on the tread. You may also feel the steering shudder after hitting a bump if the shocks are worn.
A "bounce test" will usually tell you if your shocks or struts are worn. Rock the suspension up and down several times, then release it. If the shocks are good, the vehicle should stop rocking almost immediately. But if it continues to rock up and down several times, you need new shocks or struts.
When visually inspecting the shocks and struts, look for:
Aggressive Driving
Tires don't last long on race cars, so they may need to be changed several times during a race. The same is true for tires on a vehicle that is driven aggressively. Hard cornering, spinning teh tires when accelerating, and standing on the brakes can all wear tread off the tires very quickly. Teenage drivers and people who drive pizza delivery vehicles can wear out tires extremely fast. Changing your driving habits can extend tire life and save you the cost of having to replace your tires prematurely.
Cheap Tires With a Rubber Compound That Is Too Soft
The ingredients that go into the rubber compound to make the tread have a huge bearing on how well a tire resist's wear. The higher the amount of carbon black, the tougher the tread and the longer it lasts. But the trade off may be increased ride harshness and loss of dry traction. So a tire manufacturer chooses a compound that optimizes traction and tread wear. Cheaper tires as well as racing tires typically use softer rubber compounds. Soft rubber is good for dry traction, but not for wear resistance.
Tires will low treadwear ratings (less than 200) will not last as many miles as tires with high treadwear ratings (over 300). The higher the treadwear rating, the more miles you should get from the tires. The treadwear rating can be found on the tire sidewall.
|
WARNING: DO NOT USE OIL, GREASE, ANTI-SEIZE OR LUBRICANTS ON LUG NUTS WHEN CHANGING TIRES 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 CLEANand 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. |
Did You Find This Article Helpful?
If so, a small donation (even $1) would help underwrite the cost of maintaining this website, and allow us to provide even more free automotive content.
To make a donation, use the button below and fill in an amount. Thanks!
More Tire Articles:
Click Here to See More Carley Automotive Technical Articles