Brake system changes affect tire wear

As truck and truck trailer brake systems evolve, they're bound to affect not only what tires we buy but how they perform. More aggressive steer-axle brakes, heavy-duty air disc brakes, engine compression brakes and electronic brake-by-wire systems are going to impact wear rates and wear patterns.

Before antilock came on the scene, steer axle brakes were generally undersized. Some were disconnected. It was considered preferable to maintain steering control in an emergency rather than risk the loss of lateral traction caused by a skidding front tire.

With little or no braking torque available for transfer through the single-mount steer tires, the irregular wear patterns characteristic of free-rolling tires became common. Tire makers developed a variety of fixes, ranging from innovative technology to tires designed specifically for steer axle use.

Trailer tires have become even more specialized and axle-specific. Since these tires don't steer the truck and are mounted as duals, they're not subject to high side loads or cornering forces. Consequently, premium trailer tires have shallow treads and relatively simple pattern designs to maximize long, even wear.

Drive-axle tires have traditionally transferred most of the vehicle braking forces through their footprint or road contact patches. In addition, they drive the truck by accelerating or maintaining speed while overcoming aerodynamic and frictional forces. Because they bear the lion's share of torque transfer, both power and braking, drive tires are designed with deep treads and minimal susceptibility to irregular wear. High-mileage drive tires typically have about twice the tread depth of trailer tires.

As a general rule, the greater the magnitude and variety of forces transferred through the tire footprint, the less fragile the tire becomes in resisting unwanted wear-pattern development. This is good news for truckers, given the trend to brake system upgrades. Spec'ing ABS on steer axles makes it possible to use larger, more powerful brakes, which will retard the development of irregular wear. Since ABS tends to equalize braking torque at each axle end and limit brake effort just short of wheel lock, the probability of brake skids is reduced considerably.

Brake-by-wire systems now under development will electronically signal the trail, drive and steer axles when braking action is needed. Brakes will be activated using the application timing by axle and degree of retarding force that best suits the variety of vehicle and road conditions present. This will reduce the brake response time of today's systems, with their long brake lines carrying compressed air to the axles.

Keep in mind that trailer brakes normally apply first, followed by drive axle and then steer axle brakes. With electronic controls, this application sequence should happen more quickly and consistently. We'll see evidence of this in more consistent stopping distances and fewer instances of abusive, brake-induced tire wear.

Another trend that can affect tire wear is the increasing popularity of auxiliary engine brakes, which apply braking force only through the drive tires. Truck engineers estimate that 80% of today's new Class 8 trucks are equipped with these devices, which are typically used to assist the regular braking system. Aggressive use of these brakes can increase overall drive tire wear, although there's also a tendency to reduce any directional torque induced patterns such as heel/toe wear.

Changes in heavy-duty truck brake systems can, and likely will, affect the rates and patterns of tire wear. So far, most of the changes seem to be for the better. Let's hope that trend continues.