While the wheel hasn't changed much in millions of years, truck and trailer tires can provide a mountain of data to a technician who knows how to interpret it – and you don't even have to plug in, connect or log on to get the information.
With more than 100 years of accumulated maintenance experience and hard science as a guide, a good technician examining a tire can discern a wide array of problems quickly, such as questionable driver behavior, alignment issues, worn components and improperly spec’d tires.
Just like walking on an injured foot or leg for an extended period can cause irregular wear on a shoe, the same thing too can happen to tires. Whether it’s a toe problem or a camber problem, or if it’s a drive axle misalignment problem, it’s going to show up in your tires.
Tires represent a significant investment for fleets. It's usually a motor carrier's third highest expense behind salary and fuel, and when it comes to tire wear drivers are a fleet’s first line of defense, according to Michelin. All drivers should include a comprehensive tire examination in pre- and post-trip inspections. During those inspections, they need to get “up close and personal,” rubbing their hands on the tires to check for any feathering, cupping or diagonal wear.
There also might be a more personal reason for drivers to monitor tire wear, because tires can expose bad driving habits and their own poor tire care. Tires easily can indicate driver practices such as high-power or jackrabbit starts, brake skids or lack of regular inflation.
If you have spec’d a tire improperly, you will quickly see an increased wear rate, says Continental. If a fleet has selected a tire that isn’t right for the application – such as a regional tire optimized against cutting and chips that is being used in a slow wearing application – tramline wear would be evident.
“Tires are getting more specialized all the time, according to Goodyear. We now have tires that are best suited for high-scrub applications – a great example would be a school bus – that are constantly turning left and right, with lots of starts and stops. The tires go through a lot of scrubbing in all those tight turns. Goodyear designs high-scrub tires with a tread compound that wears “as well as it can in that situation,” Goodyear says. “It’s going to resist the scrubbing. If you didn’t have that tire on, you’re probably going to burn your tires off pretty quickly because you have the wrong tire for the application.”
Tires, like vehicles, have become very application-specific in recent years, according to Double Coin. Different patterns, sizes, designs and components of a tire offer the vehicle the best productivity and efficiency in a specific application. If mismatched, many times the tire, and sometimes the vehicle, will show the results.
No matter how thorough a fleet’s inspection process, it’s not enough if drivers don’t act quickly to avert catastrophic tire damage when something unforeseen happens. If a truck has an air pressure monitoring system that warns of slow or sudden air pressure loss, the driver should pull over as soon as possible to prevent further tire damage – as well as potential damage to the truck or nearby cars. If no PSI monitoring system is available, it is difficult for a driver to do anything unless noise, vibration or altered performance is felt in the cab.
The bottom line? Not taking the time to examine tires – or ignoring the problems the tires are identifying – not only increases tire acquisition and replacement costs but also allows vehicle issues to get out of hand and become safety issues.
Diagonal wear typically shows up as localized flat spots that cross the tread of a tire in a diagonal pattern. Diagonal wear generally is inflicted by mechanical forces from the drivetrain affecting the tire. Because they repeat in a frequency, they continually show up in the same locations on the tire. Some examples could be worn or improperly adjusted bearings, or differing overall tire diameters combined in the dual position; this could be a mismatch or improper inflation. Diagonal wear often is slow to develop and can be aggravated by alignment issues.
Thrust/scrub angle wear
Thrust angle issues occur when a truck’s drive axles, through improper alignment, cause the truck to want to deviate from a straight path; the drive axles are attempting to thrust the truck out of line, and the driver constantly has to correct for this with the steering wheel. Thrust angle tends to show itself when one steer tire is worn on its inside and the other is worn on the outside. This is different from toe wear’s symmetrical wear pattern; with thrust angle, wear is independent of the side of the truck where the tire is located. Accelerated wear is found on the outside of one drive tire, and on the inside of the opposite drive tire.
Similar to thrust angle wear, dog tracking occurs when a tractor’s rear axles are not aligned properly with the axles of the trailer it is pulling; the tractor is attempting to drive down the road in a straight line, while the trailer behind is attempting to track off a few degrees to the right or left. In severe cases, dog tracking can be so bad a driver on a straight road can see more of one side of the trailer in his rearview mirrors than the other. Signs of dog tracking easily are confused with thrust angle wear. The best way to determine the correct problem is to evaluate the vehicle’s driving characteristics: If the truck pulls constantly in one direction, the problem is in the mounting of the drive axles. If the vehicle wanders all over the road, the problem is most likely an alignment issue in the trailer axles.
Tandems should be square when they’re mounted properly on a vehicle; they should be perpendicular to the frame and parallel to each other. Scrub comes into play when one of the axles is not parallel to the other axle. So a tire on one side of the vehicle is rolling in a larger diameter than on the other side, causing the vehicle to attempt to turn in circles, creating an extremely tortuous condition for the tire in question. Scrub angle problems generally show up as diagonal wear across the tread of a tire. But diagnosing the condition can be tricky as worn axle components also show up as diagonal wear.
Most sidewall wear is damage-related, primarily from scrubbing or curbing. Driver practices are usually the key to avoiding this type of damage, although in some applications where curbing is a given – such as tight urban surroundings – a fleet may want tires with features that can withstand additional curbing, such as protective curb ribs. Excessive curbing can cause pinch shock, a condition where a tire’s sidewall is subjected to abnormally heavy loads, resulting in a crimped core. It’s like bending a coat hanger and then trying to restore it to its original state; the wire can’t be straightened back out. Likewise, the tire’s core stays “pinched,” accelerating abnormal wear and weakening the tire’s overall integrity.
Feather wear is easy to detect – but a technician actually has to put his hands on the tire and rub them up and down to diagnose this problem correctly. Generally speaking, feather wear is an alignment issue, usually because of a bad toe condition. Toe-in occurs where two tires are turned in so their front edges are closer together than the rear edge. Toe-out is the opposite condition. The wear pattern is similar to the way a bird’s feathers overlap: when a technician rubs his hand over the tire, he will feel it’s smooth in one direction, and rough when he rubs his hand back against the grain created by the toe condition. A good rule of thumb: Smooth-in means a toe-in condition, while smooth-out means toe-out. Feather wear also can be caused by side-scrubbing or severe drive axle misalignment.
Camber is the outward or inward tilt of a tire. Tires should be straight up and down. If they are tilted in at the top, that is negative camber. If they are tilted in at the bottom, that’s positive camber. Although a little positive camber is desired for a loaded vehicle, the tires have a tendency to go negative. Too much positive camber will lead to smooth wear, usually on the outside of one of the tires. Too much negative camber will lead to smooth wear, usually on the inside of one of the tires, and it can be severe enough that it’ll be found on both tires. In most cases, the symptoms are seen on one tire only.
Cupping results from an up-and-down motion affecting the tire and its contact with the road surface. A bad shock absorber, air springs or suspension system usually is to blame, creating vibrations that cause the tire to “bounce” up and down as it travels down the road. This type of wear usually shows up on the steer and trailer tires and appears as a series of high and low spots around the tire’s tread surface.
As the name of this condition indicates, flat-spotting starts off as a single, scrubbed band of tread running across the tire that is shallower than the tread area immediately surrounding it. This affected area clearly will be “flatter” than the tire surface surrounding it. In most cases, flat-spotting is created by a brake issue; most of the time, a foundation brake is locked up or dragging, although a severe panic stop – or a driver who has a habit of overaggressive braking – can create the problem. If a brake check fails to identify any maintenance issues, a safety refresher with the driver may be in order to moderate his braking habits.