The goal of fleets when it comes to their tire program is to maximize tire removal miles and fuel economy. This keeps the fleet maintenance budget and fuel costs in line.
To get optimum removal mileage, tires must wear smooth and evenly. If irregular wear develops, tire fuel economy will also suffer. Any signs of uneven and irregular wear should be considered an early warning sign that there are other issues either with the vehicle or tire/wheel assembly that need to be addressed.
This is why it is so important that tires are visually inspected on a regular basis. Such inspections are also important because, as we all know, steer, drive and trailer tires all have unique irregular wear issues that can develop.
Steer tires are the most sensitive when it comes to developing uneven wear. Shoulder step or more commonly called ‘chamfer wear,’ is where there is ‘step’ (depressed) wear in the shoulders. This is confined to the outer portion of the shoulder rib. It can occur in either one or both shoulders.
Tires run in line-haul operations tend to see this type of wear, especially if the specific tire tread pattern does not have a ‘defense’ or pressure distribution groove. This condition will not affect overall mileage or fuel economy, and it is not something that requires the tire to be replaced.
Full shoulder wear is another story. This excessive wear extends over one or both shoulders, and is usually related to misalignment. If there is excessive axle toe-in, the outside shoulder of both steer tires will be worn. If there is too much toe-out, then the inside shoulder of both steer tires are worn.
If you find one steer tire has inside shoulder wear and the other steer tire has outside shoulder wear, then the diagnosis is the drive axles are misaligned. Sometimes poorly maintained suspension components can produce similar tire results. On rare occasions, improperly seated beads will also lead to the same irregular shoulder wear.
Another alignment-related condition that is common for steer tires is "one-sided" wear. This is defined as excessive or fast wear extending from one shoulder gradually to the other shoulder. Drive axle misalignment is usually the culprit. If you measure the tread depth in each groove and the measurement keeps getting smaller, then you know it is time to check the vehicle alignment.
Feather wear is also found on steer tires that have excessive toe and/or drive axle misalignment. Feather wear is the condition where each individual rib is worn high to low. Excessive side force scrubbing is the cause of feather wear and this not only affects tire removal miles, but fuel economy is also significantly reduced.
If you find tires that have shoulder cupping that creates a scalloped appearance then this indicates an out-of-balance condition. If the tire is also underinflated, this can magnify this problem. Too much wheel-end bearing play will also contribute to this shoulder cupping condition. You will need to diagnose this imbalance condition, which may include the wheel, hub, and/or brake drum.
Depressed rib wear or punch wear can be found on steer tires that are run underinflated. Improper tire bead seating and assembly out-of-balance can also generate this tread condition. Usually one rib is depressed compared to an adjacent rib. It is an easy condition to spot. Maintaining proper tire inflation pressure based on the load will usually minimize this condition.
There are many different drive tire tread patterns available in the market. The common denominator is the lugs. If there is rapid shoulder wear on only the inside shoulder of an inside dual tire then negative axle camber under full load may be a contributing factor. Axle-flex under load and misadjusted bearings need to be checked. Also, if there is uneven inflation pressure between the duals, this can also lead to this condition.
If you have a vehicle running superwide tires on the drive position and both shoulders have fast wear then the tires are overinflated. Superwide tires are sensitive to running at pressures based on the load. When you add too much air, the shoulders are not in contact with the ground, which leads to shoulder scuffing and fast shoulder wear.
Heel/toe wear is found on dual drive tires that have mismatched tires and/or mismatched inflation pressures. Heel/toe wear can be described where each lug is worn high to low from the front to back edge. This condition is very easy to eliminate. Ensure that when you replace only one tire of a set of duals that the overall circumference is as similar as possible. The worst case scenario is installing a new drive tire next to a worn drive tire. If the overall circumferences and tire pressures are not equivalent then the heel/toe wear will become more severe.
Alternate lug wear is another irregular wear condition found on drive tires. It is caused by the same conditions just described regarding heel/toe wear.
When it comes to trailer tires there many irregular wear conditions that develop simply because this is the most neglected of all wheel positions. Many fleets do not own their own trailers and, as a result, are not checking tire pressures and conditions on a regular basis and have minimal visual inspections.
If you see a tire with a localized spot of excessive wear across the tread face that may even extend into the casing, then this is considered a brake skid. New brakes, aggressive use of brakes, and driver abuse such as using only trailer brakes to stop a vehicle will all lead to brake skids. Driver education will help minimize this condition.
Diagonal wear is represented by localized flat spots worn diagonally across the tread. These diagonal spots will repeat around the tire. In most cases this condition develops as a result of a minor brake skid and progressively gets worse. This can also occur because of loose wheel bearing and a toe-out condition.
The two irregular wear conditions for trailer tires directly related to alignment issues are rapid wear on one shoulder and one-sided wear. Excessive camber will lead to rapid shoulder on one shoulder. One-sided wear the measured tread depth of each groove diminishes as you go across the tread surface is usually caused by too much toe. Very few fleets actually check trailer alignment but if you come across either of these two irregular wear conditions then it is an early warning sign to perform a trailer alignment.
Another common condition seen in trailer tires is called multiple flat spot wear. There are numerous areas worn around the tire. These tires just look ugly. When trailer tires are not maintained for inflation pressure, mismatched inflation pressures, driver abuse of trailer brakes, and empty loads all contribute to this trailer tire irregular wear.
Training drivers and vehicle service technicians to visually inspect tires and measure inflation pressure on a regular basis is the best way to identify irregular wear conditions at an early stage.
Understanding the probable causes of the specific irregular wear condition will allow your fleet customers to make the proper vehicle corrections to ensure that they maximize tire removal miles and fuel economy.