Auto Academy: Tire Wear and Rotation

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Michelin_Tires

Source: Michelin

If you’ve noticed that your car doesn’t feel right as you’re driving down the road, then you may need a wheel alignment. Now, it’s usually only necessary to get an alignment if you purchase new tires, but if your ride is a bit off, and you notice an unusual pattern of wear on the tires, you should make for your mechanic’s as quickly as you can. If you know what you’re looking for, tire wear patterns can actually tell you quite a bit about the alignment of your vehicle and what you might be in for. Today, we’re going to explore these wear patterns, talk about what they mean, and explore how best to rotate your tires to extend their life.

Shoulder wear

There are two different types of shoulder wear that you should watch for. If you observe your tires with less tread depth on both shoulders (the inner- and outermost treads before the sidewalls), that tends to indicate that your tires are under-inflated. Tires are designed to provide maximum contact with the road surface at a specific pressure. Additional load will be applied to the shoulders of the tire if they’re under-inflated. These tires will appear to bulge out between the tire and the road. That said, do NOT attempt to use this as a way to measure your tire pressure. Tire pressure gauges are cheap insurance for your tires. Measure pressures when the tires are cold (meaning before you drive) and ensure that you are resetting the gauge before each measurement.

If you notice wear on only one shoulder, it usually indicates that your vehicle has excessive camber on the wheel that is showing the wear. Negative camber will cause wear on the inner shoulder and positive camber on the outer. This condition can also be caused by broken suspension/steering components, but an out-of-alignment condition is a good bet.

Source: Bridgestone

Source: Bridgestone

Tread wear

If you look at your tire and see that the center part of it, the tread, is worn down, but the shoulders look less worn, it tends to indicate that your tire is overinflated. Over inflating a tire causes it to expand, but the sidewalls are not capable of expanding as much as the tread. This results in the tread of the tire contacting the road exclusively, which accelerates wear. Use a tire pressure gauge to verify that your tires are set to the appropriate pressures.

Tip: If you don’t know what pressure your tires should be set to, look at owner’s manual or the sticker on the rear of the driver’s side door jamb.

Source: Bridgestone

Source: Bridgestone

Feathered wear

If you see a wear pattern that appears to go diagonally across the tire with tread blocks that are higher on one side, like a sawtooth pattern, it will usually indicate either an incorrect toe setting or a broken suspension component. This pattern is often easier to detect by feel rather than visually. If the feathering is going outward, your wheels might have toe-out. If the feathering is going inward, the wheels are probably excessively toed-in. This wear pattern can also occur during high-speed cornering, especially if understeer is present. If your car starts to understeer, it will create a similar sideways wear pattern on the tire. So if you’re street racing the family minivan on the weekend, beware of feathered tires.

Cupping

Cupping is almost always an indication that something is broken, typically the shock absorber. As I discussed in my piece on magnetorheological suspensions, the shock absorber keeps the vehicle from continuing to bounce after it goes over a bump. If the shock absorber has failed, the car will bounce down the road, which can lead to a cupping pattern, which increases road noise and look like your tires have had someone scoop a chunk of rubber out of it. If the wheel/tire is unbalanced, it could lead to cupping as well, but that’s not as likely. Just to be sure, if your tires are cupping and you can’t immediately identify a broken suspension component, it’s worth checking the wheel and tire balance.

Source: Cooper Tire

Source: Cooper Tire

Tire rotations — correct patterns

The front wheels of a vehicle, especially if it’s front-wheel drive, have a vastly different job compared to the rear wheels. Tire rotations ensure that the workload is spread across all four tires evenly. This is analogous to different cyclists riding in the front in a peloton. The person in the front has to work harder to fight the air resistance, so it makes sense to rotate regularly (for tires, regularly is every 3-6,000 miles). The question that often comes up with tire rotations is “How should I rotate my tires?” The answer is that it depends upon your vehicle. You should always follow the manufacturer’s specifications. There are a number of different approved tire rotation patterns and I will explain who they are designed for.

Rearward cross

This pattern involves switching sides for the the front wheels as they move to the rear (RF to LR, LF to RR) while moving the rear wheels to the front on the same side (RR to RF, LR to LF). An accepted alternative to this is the Cross or X Pattern, which switches sides for all four wheels (RF to LR, LF to RR, LR to RF, RR to LF)

Best for: rear-wheel drive, four-wheel drive, and all-wheel drive vehicles.

Forward Cross

As I’m sure you can guess based on the name, this is the reverse of the rearward cross. In the forward cross, the rear wheels switch sides as they move to the front (LR to RF, RR to LF) and the front wheels move to the rear on the same side (RF to RR, LF to LR).

Best for: front-wheel drive vehicles

With any of these patterns, it’s easy to see how the wheels will quickly experience all four corners. This is obviously a problem if you have directional tires, which should be swapped front and back on the same side, or if you have a vehicle that does not have four wheels/tires of the same size, like some AWD vehicles, which should be swapped side to side on the same axle.

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