Tampa Spring Company

Heavy duty truck and trailer suspension parts and repairs.


 

Inspect Tires for Wear

1. Refer to your owner's manual for the manufacturer's recommended tire pressure. You might also find this information on a sticker in the glove box or on the driver's door jamb.
2. Use a gauge to check the air pressure in each tire. Add air or deflate as needed to match the manufacturer's recommendation.
3. Look in the grooves between tire tread for raised patches of rubber, called wear bars. These 2/32-inch tall patches will help you identify a worn out tire. (In most states 3/32-inch is the mimimun legal tread depth.)
4. If tread is worn to a level where wear bars are flush with the tread it indicates that tread depth is 2/32-inch or less. Replace worn tires.
5. If your tires do not have wear bars, place a US penny into a groove between treads, with Lincoln's head down. If the tread is at or beyond the top of Lincoln's head you have at at least 3/32-inch of tread left, a satisfactory level.
6. Tread should wear evenly. Inspect each tire for unusual tread wear. A rounded edge on the inside and outside edges of tread could indicate under-inflation.
7. The same wear pattern on front tires of front-wheel drive vehicles could indicate a need for more frequent tire rotation.
8. Excessive wear on the center of a tire's tread could indicate over-inflation.
9. Unusual wear that resembles a chop or stair-step pattern could indicate worn shocks.
10. Excessive wear on the inside or the outside of the tread could indicate the need for alignment.
11. Carefully check each tire for punctures, nails, damage, scuffs, and weather cracking. Repair or replace as necessary.
Pressure stats printed on sidewalls indicate the maximum amount of air pressure tires should be inflated with -- not recommended pressures.
Check your owner's manual or ask your local tire dealer for tire rotation recommendations.

 

Have you ever wondered if there are any advantages to wheel alignment other than making tires last longer or reducing steering effort? These are the usual reasons to consider front tire/wheel alignment. First is tire wear. Tires are expensive on any vehicle, but for large, diesel powered rigs, prematurely worn out tires can add significantly to the operating cost. The second most important reason for aligning the front tires is to reduce steering drift, turning effort, and to improve the trackability of the truck. However, there is a third important reason to keep front tires in proper alignment: Fuel economy is affected by improperly aligned tires.  A diesel powered truck is "pushed," that is, it is a rear wheel driven vehicle. The driving forces come from the rear of the truck. As the truck is pushed, the front tires have a certain amount of rolling friction between the tire surface and the roadway. This results in what is known as "drag." See illustration #1.


Illustration 1

As the vehicle rolls forward, the drag causes the tires to want to move outwardly. This outward motion is a result of the normal-tolerance, steering-linkage free-play. Thus, when the vehicle is in a static (non-moving) state, the tires are "aligned" so that the front leading edges of the tires are closer together than the rear trailing tire edges. See illustration #2. This condition is known as a toe-in setting.







IIlustration 2

If the toe setting is improper - excessive or insufficient - the tires will not roll in a parallel fashion; thus, the road friction force will cause wear to the tire. As a result, energy will be lost since the tire fights the truck's intended path-of-travel. The lateral, side forces cause tire wear. We can see the result on the tires, but it is not always easy to see the result on fuel economy.


 

Tires which are improperly toe-aligned can account for two increased operational expenses: (1). decreased tire life, and (2). decreased fuel economy. Tires out-of-toe adjustment by 1/8 inch will wear significantly faster. Depending on the size of the tire and load of the truck, tire life could be reduced as much as half. The effective use of fuel could be reduced from one or two tenths miles per gallon (MPG) or up to three or more tenths MPG. A typical 11:00 X 24.5, 10-ply, new front radial tire costs approximately $260.00. A misaligned front end that adds ten percent (10%) drag will decrease tire life by ten percent (10%). 


Illustration 3

Only a slight misadjusted toe setting could cause a ten percent (10%) additional drag. If a typical over-the-road truck delivers six (6) MPG, 2/10 MPG represents a 3.33% increase in operational expense.


For example, a truck which operates 50,000 miles per year and averages 6 MPG would have an annual fuel cost of $10,416.66 if diesel costs $1.25 per gallon. If the MPG were lowered to 5.8 due to improper alignment, then fuel cost would increase to $10,775.86 or by $359.20. A second front end misalignment that will increase tire wear and decrease fuel MPG is tire camber. Camber is the tilt of the tire in a vertical plane. If the tops of the tires are farther away from each other, then the tires are said to be aligned with positive camber. If the tops of the tires are closer together, the tires are said to have negative camber. See illustration 3.

 


 

Most large trucks use a very slight positive camber setting, usually less than 1°. Camber evenly distributes the truck's load across the two wheel bearings and assists in keeping the truck from drifting slightly when tracked in a straight line. Insufficient or excessive camber shifts the load to one edge of the tire resulting in excessive shoulder wear. See illustration #4.


 

Excessive unequal camber will cause the truck to pull toward one side. To keep the truck on path, the driver will have to compensate by turning the wheel. The need for the slight off-center steering force to keep the truck in a straight line results in excessive drag and, subsequently, decreased MPG. Some manufacturers recommend a small camber difference to compensate for crowned roads. This difference is usually less than 1°.
 
 





Illustration #4, Courtesy of Moog Automotive, Inc

ACTIVITY:
Study the illustrations below for typical tire wear problems. Notice how each wear pattern is different from each other. For example, excessive toe-in wear creates a "feathered" saw-tooth effect across the tread.
       

       
Illustrations Courtesy of Moog Automotive, Inc.
WORN FRONT SUSPENSION COMPONENTS =
TIRE WEAR = HIGHER FUEL CONSUMPTION
Normal Tire Conditions: Gradual tire wear is normal; flat, even tire wear is a sign of correct alignment, tire balance, and proper inflation.

Alignment Purpose: Alignment compensates for slight normal front suspension tolerance and component wear in king pins, bushings, tire rod ends, steering gear, and springs that sag.

Lubrication: Regular lubrication prevents or defers wear to these components. Not only is it important to lubricate the front suspension at correct intervals, but it is also very important to use the correct type of lubricant.

Misalignment Indicators: Tires with even the slightest edge wear, cupping, or spotty wear are exhibiting signs of misalignment. This misalignment may be a result of either poor alignment settings or worn parts that create a misaligned front suspension.

Energy Savings: Tire scrub, a lateral force that pushes the tire sideways, adds to the rolling resistance of the vehicle. As a result, more energy is required to move the vehicle in its intended path of travel. Tires are constructed from petroleum stock; therefore, if tires wear out prematurely, natural resources are wasted.

Balance:
Tire and wheel balance compensates for static and dynamic unbalance of wheels and tires. Unbalanced tires bounce and lose contact with the road. The "heavy side" of the tire comes in contact with the road and small excessive amounts of the rubber are rubbed off.

Improper Inflation:
Improper inflation, too low or too high, may also result in excessive tire wear. Underinflating wears out the edges of the tire and adds to tire drag. Fuel is wasted due to increased drag. Overinflation wears the tire in the center. The illustrations below portray road contact and wear patterns when tires are:
Illustrations courtesy of Moog Automotive.

Tire Wear:
Heavy, spotty, cupped or irregular tire wear are signs of components of king pins, bushings, tire rod ends, steering gear, pitman arms, idler arm, spring sag, shock leakage, or wheel bearings that are out of specification. Figures 1, 2, 3, and 4, identify each type tire wear problem.
Figure 1 
Figure 2 Improper Toe causes this tire wear
       



An improperly set camber caused this tire wear.

Combination of factors caused these tires to wear:
Figure 3
       

Worn / loose king pins plus an incorrect camber

could cause this tire wear pattern.

Figure 4
Worn / loose king pins plus a toe-out condition would cause this tire wear pattern.
Tire Illustrations Figure 1, 2, 3, and 4 courtesy of Moog Automotive.

Misalignment is the second leading cause of lost tread mileage after improper inflation.


Most people focus on only the steer axle when steer tires are wearing funny. But a large percentage of the time, the misalignment problem can be located in the tractor drive axles as well as the trailer axles.


The science of tire wear


Irregular wear patterns are caused by abrasion that is concentrated in one area of the tire tread instead of across the entire footprint. Side forces created by turning, off tracking, incorrect toe, etc. can drag or slip the tire across the pavement and concentrate wear on one side of the tire or one side of the ribs. Steer tires tell most of the story when it comes to alignment. Steer tires are always affected when the steer axle is out of alignment as well as when the rear axles are pushing the vehicle in a direction other than straight.


You can diagnose the cause of misalignment-induced, irregular wear by feeling the tread with your palm and fingertips. To do this, lightly move the palm of your hand around the tire tread circumferentially. Then move across the tread laterally, sensing feather edges and differences in tread element depths.


Circumferential readings allow you to determine heel/toe wear and cupping/scallop wear, which are not alignment-related conditions. Lateral readings tell you which way the tread is feather edged. If the feathered edges are in the same direction, the misalignment is caused by torque thrust and if they are in the opposite direction, either toe or camber causes the condition.


Toe setting is the first and foremost factor that affects steer tire wear. Toe refers to the inward or outward pointing of the wheels when viewed from the top of the vehicle. It is the difference in distance between the centers of the front and the rear of the wheels as seen in a top view of the truck.


Toe-in exists when the wheels are closer together in the front than in the rear. A little toe-in is necessary to compensate for the tendency of the wheels to deflect rearward as the vehicle is loaded and while it is in motion. Due to this tendency, the wheels of a vehicle with properly adjusted toe-in are traveling straight ahead when the vehicle itself is traveling straight ahead. This results in directional stability and minimum tire wear.


With toe-out, the wheels are closer together in the rear. While a little positive toe is necessary for improved tread life, negative toe accelerates tread wear.


Toe is the most critical alignment setting. An eighth-inch of toe adjustment error results in 11.5 feet per mile of sideslip. Excessive toe-in results in full shoulder wear—excessive wear across one shoulder—on the outside shoulders on both tires. Excessive toe-out results in full shoulder wear on the inside shoulders of both tires.


If feather wear is evident where the tread appears to be worn high to low on each rib across the tread face, a severe toe condition or worn steering components are to blame. When running your hand across the tread, an easy rhyme to remember is, “Smooth in-Toe-in” and “Smooth out-Toe-out.” (You won’t hear rocket scientists singing this rhyme, but if it helps you, go with it.)


Check alignment


The second most common cause of irregular wear is rear axle alignment. On a properly aligned vehicle, all the axles should be perpendicular to the frame and parallel to each other, and all the wheels should track the front wheels.


Tandem drive axles that are not parallel to each other and axles that are not perpendicular to the chassis centerline are the two primary misalignment conditions that affect vehicle tracking and have a definite effect on steer tire wear.


Rear tandem axles that are not perpendicular or “square” to the frame but are parallel to each other create a “thrust angle,” which tends to push the vehicle off course. The driver feels the vehicle pulling in the direction the drive axles are angled and must steer in the opposite direction to keep the truck traveling in a straight line.


The steer axle tires are constantly subjected to “scrubbing” or side forces as they continually correct the direction of travel of the truck, which results in fast and irregular wear.


This condition on trailers is known as “dog tracking” and is quite visible as you follow the vehicle down the highway since the trailer appears to be traveling at an angle to the tractor. The driver feels the vehicle “wandering” and must make constant steering corrections to keep driving straight ahead.


Tires on a trailer with this condition are dragged sideways a few feet for every mile of operation. In severe conditions, this can result in dragging the trailer tires sideways for thousands of miles for every 100,000 miles the vehicle runs.


Tandem skew, or scrub angle, occurs when tandem axles are not parallel to one another. Non-parallel axles cause all the axles to work against each other. The steer axle must be turned to compensate for the push of the rear axles to keep the vehicle moving in a straight path. Drive axles will fight each other to determine the direction the vehicle will go. Trailer axles with tandem skew will be dragged in different directions.


Drive axles rarely ever exhibit irregular tread caused by misaligned axles. More often than not, tires on the steer axle fall victim to irregular wear as a result of misalignment in other parts of the tractor-trailer combination. One early indication of tandem thrust is having both steer tires feather in the same direction, as opposed to toe which causes feathering in opposite directions.


One-sided wear—which is excessive wear on one side of the tire extending from the shoulder towards the center of the tread—is a more severe wear pattern caused by drive axle thrust angle. In both cases the drive axle pushes the vehicle either to the right or the left, and the driver has to compensate by steering in the opposite direction to keep the vehicle traveling straight.


This results in abrasion on the outside shoulder of one steer tire and the inside shoulder of the other steer tire.


Trailer tires, however, do exhibit irregular wear as a result of poor alignment. Rapid shoulder wear on one shoulder of all the tires on an axle can be caused by an axle that is not “square” to the frame. Tires are worn on the edge of one shoulder, and wear can sometimes extend into the inner ribs.


In this condition, both dual tires on one side of the axle are worn on the outside shoulder and the inside shoulder of both of the tires on the other side of the axle. One-sided wear on trailer tires, which appears as excessive wear on one side of the tread, can be caused by non-parallel axles as well as excessive toe.


The problem is that toe cannot usually be adjusted on drive and trailer axles—only on steer axles. So you’d better hope that the axle is not perpendicular to the frame, since that situation cannot be corrected.


Camber’s role in tire wear


Camber is the third leading misalignment cause of irregular wear. Camber is the inward or outward tilt of the top of the tires when viewed from the front of the vehicle.


The tops of tires on vehicles with positive camber are farther apart than the bottoms of the tires. Negative camber results in the bottoms of the tires being farther apart than the tops of the tires. Excessive positive camber will wear the tread on the outer half of the tire while negative camber will wear the tread on the inner half of the tire.


Excessive camber can cause steer axle tires to exhibit one-sided wear and trailer tires to develop rapid shoulder wear—one shoulder and one-sided wear in more extreme cases. In rare cases, drive axles that have been bent and have way too much camber can wear the outside shoulders of the drive tires, too.


Know when to align


As you can see, checking alignment requires that the entire vehicle be checked, not just the steer axle. So the next time you think that the steer tires must be bad because steer axle alignment checked out OK, have your drive and trailer axles checked as well. That is probably where the problem is.


The Technology and Maintenance Council (TMC) recommends the first alignment be done at 15,000-30,0000 miles but no longer than 90 days after the vehicle is put into service. Subsequent alignments should be done at 80,000- to 100,000-mile intervals or intervals of 12 to 18 months—whichever comes first.


Alignment also should be checked any time a component that affects alignment is replaced.