Diagnosing Irregular Wear - Tire Review Magazine

Diagnosing Irregular Wear

New column devoted to helping front

As the title of this new monthly column suggests, this article is meant for tire technicians only. So if you are not a tire tech, you may want to move along to the next article.

Okay, now that we’ve gotten rid of the civilians…

So you’re a tire technician. Congratulations. You do an important job and are generally unrecognized for it. Customers think you’re a grunt, except for the really hardcore tire and wheel geeks – they think you’re dangerous. Your manager probably thinks anyone could do your job, and your family wants you to wash off that brake dust right now.

But it is your heroic brilliance at keeping people alive and well on our nation’s highways that goes heart-rendingly unnoticed by the vast majority of the driving public.

While we can’t do much with the consuming public, we can help you better understand and appreciate the vital role you play as the front-line person handling a customer’s vehicle.

You mount new tires, deal with NVH and ride issues, troubleshoot all manner of pulls and pushes and such, repair nail holes (properly, I hope), deal with TPMS resets, relearns and replacements – just about everything tire-related in every tire shop across the continent.

What I can do is use the 10 years I spent training and managing tire techs to accomplish two goals. The first is to remind you of how important your job is. Lives literally depend on what you do. With great air pressure comes great responsibility.

The second is to talk about some of the things you really need to know to do your job better. There are many aspects of a tire technician’s job that don’t always get taught, even by TIA or by the ASE Tire Tech certification course, but will only come through experience. That’s this new column’s goal.

We’re assembling a team of true tire service experts that I will call on to provide tips, techniques, advice and real-world situations to help all tire techs become zen tire masters.

We’ll begin this month with some tips for diagnosing and dealing with various types of irregular tire wear. Diagnosing tire wear always begins with a visual check of the tire. This should be part of your standard operating procedure when removing the tire/wheel assemblies from a customer’s vehicle – especially when mounting new tires.

Look for excessive wear on one or both shoulders or in the center rib area. Look for signs that the tread blocks are uneven, especially if the customer has mentioned excessive tire noise or a change in the “tire song.”

Next, check the tire on the balancer. Don’t drop the balancer hood just yet – you don’t want the machine involved until you’re ready to actually balance. Instead get the tire spinning by hand to look for irregularities that are hard to see when the tire is standing still.

Getting into the details, here’s what to look for.

One Shoulder
Excessive wear on one shoulder of the tire is generally an indication of camber issues. Camber is the degree to which the tires are tilted away from being straight up-and-down. If the tire is tilted inward toward the vehicle, this is negative camber; away from the vehicle is positive camber. If the inside shoulder is worn, there is too much negative camber. If the outer shoulder is worn, there is too much positive camber. Unless the tread is worn away in the affected area, correcting the camber will start to correct the wear.

Scalloping, which some techs call ‘feathering’, is when all the tread blocks on one shoulder develop a wear pattern in which one block edge is worn lower than the other, leaving a set of raised edges on the leading or trailing edge of each block. Scalloping can be difficult to see sometimes, but can be diagnosed by laying a gloved hand lightly on the tread as the wheel spins (by hand) on the balancer. Scalloped tread blocks will produce an unmistakable ‘flutter’ as you brush your fingers over the raised edges.

Scalloping is generally a sign of incorrect camber, often indirectly caused by an impact that knocks the alignment out, and can be thought of as the start of shoulder wear. It’s possible to catch it early enough that if you correct the alignment, the tire might “wear back in” to a more normal pattern over time.


The earliest sign of this kind of wear is often an unpleasant change in the “tire song” – the noise the tire produces while driving. If the customer mentions tire noise that should be a red flag to look for scalloping.


Both Shoulders

If both shoulders are worn, the tire has been run underinflated. Because the sidewalls (below the shoulders) are more rigid than the tread, underinflated tires will tend to ride more on the shoulders and less on the tread center, creating excessive shoulder wear.



If the center is more worn than the shoulders, on the other hand, this indicates overinflation. Since the natural curve of the casing becomes more pronounced when the tire is overinflated, the center of the tread gets more wear. As the tread wears and the tire deflates somewhat over time, this leads to a concave tread profile called ‘cupping.’ Slight to moderate cupping can often be saved by proper inflation and some driving time, but with severe cupping it’s generally better to replace the tire.


Remember that a vehicle’s proper tire inflation pressure is on a placard generally placed just inside the driver’s side door. Never use the pressure embossed on a tire’s sidewall, which is the maximum cold pressure the tire can safely handle; proper inflation pressure is determined by the car manufacturer based on the car’s weight and performance, not by the tire maker.


Spot Wear

If the tire is worn in only one spot, usually on the shoulder, this is almost always due to some form of out-of-round issue. Either the wheel is bent or something is wrong inside the tire. Spin the wheel and tire manually on a balancer and look at the wheel for possible bends or other damage.


If the wheel looks straight, put your eyes at tire level and look straight across the tread as you spin it by hand. If you see an up-and-down wobble as the tire spins around, there is a problem with the tire.


At its worst, there could be a belt separation or tread delamination, in which case the situation is not repair­able and the tire must be replaced.


If the cause is a bent wheel and the wear is not excessive, the tire might be salvageable if put onto a new wheel.


Lateral Wear

While you have the tire spinning on the balancer, take the time to look at the tire treads straight on. Watch the groo­ves between tread blocks for signs of lateral wear. Grooves and tread blocks should look perfectly still as the tire spins, if you see them wiggling back and forth laterally it’s a good indication that there’s a problem with the toe.


Toe is the degree to which the tires are not parallel to the direction of the vehicle. A wheel that is “toed-in” is angled toward the vehicle, while a “toed-out” wheel is angled away.


The classic toe issue is the one that has both front tires point to the same direction, which will cause the car to pull toward one side or the other when you let go of the wheel. There is an issue when two opposite tires are either both toed-in or both toed-out. Either condition will cause the tires to essentially fight against each other, and this creates this odd side-to-side wear.


Incorrect toe can also cause the vehicle to develop an extremely annoying vibration, and the lateral tire wear caused by the toe-in can continue to cause a shake even after the alignment is corrected. This kind of wear can occur surprisingly fast; one reason why it’s important to do a four-point alignment when new tires are installed.


In future columns we’ll be discus­sing issues such as diagnosing bent wheels, avoiding installation damage, TPMS situations, mount­ing/balancing tips and other matters of interest to the folks who work where the rubber really does meet the road.


This column is for you, the mighty tire tech, and I’d love to hear from you at seanphillips45@­gmail.com with feedback, questions or suggestions for issues that we should be covering.


Now stand tall, and wash off that brake dust before your family sees you.

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