Plantan believes the 2011 regulations will be painless because commercial vehicle ABS is a proven, dependable technology, and compatibility issues are being addressed by brake OEMs. “On top of that, we have much better technology in brake systems and better thermal capacity today,” he says. A typical 6-by-4 tractor already has good stopping distance characteristics – typically in the 275- to 290-foot range. “In actuality, we’re only seeing about a 15 percent improvement in government-mandated stopping capability.”
Air disc mandate?
Air disc brake systems have been available for commercial vehicles since the 1970s. The technology initially suffered teething problems, but brake manufacturers say today’s air disc brakes are highly dependable and reliable with superior stopping characteristics that make them an obvious candidate for fleets wanting to make certain they are in compliance with the new regulations next year.
Petresh is a strong proponent of air disc technology and feels they are “clearly” superior to drum-style foundation brakes for several reasons. “Haldex has been selling them for years and has thousands of them out on the road today,” he says. “They have much lower maintenance costs than drum brakes, and they have much more life in terms of friction pads, which last much longer than standard drum brake shoes.”
Maintenance costs for replacement parts and the actual maintenance activity both are less for air disc brakes, Petresh says. “And that’s in addition to the performance advantages – the traditional point about no fade is pretty important, especially if you drive on a lot of grades, mountainous runs or severe duty cycles such as intra-city P&D or anything like that where your brake temperatures or wear rates are significantly elevated.”
Ken Kelley, vice president of Webb Wheel Products’ Aftermarket Business Unit, concedes that air disc brakes have many performance advantages, but he stresses that fleets must look at the “big picture” before switching from drum to air disc foundation brakes.
Testing results have indicated the new stopping distance regulations can be achieved by using larger S-cam drum brakes, Kelley says. Today’s standard steer axle brake size is 15 inches in diameter by 4 inches wide, but larger 16.5-by-5-inch or 16.5-by-6-inch brakes are used commonly today in vocational vehicles. “They will be a logical answer to providing more stopping torque on commercial vehicle steer axles,” he says.
On drive axles, larger 16.5-by-8-inch or even 16.5-by-85⁄8-inch brake shoes also will help provide greater stopping power and enable fleets to meet 2011 regulations without any fundamental change in business or maintenance practices, Kelley says.
“A switch to air disc brakes will involve new maintenance practices compared to S-cam brakes,” he says. Fleets also need to determine how air disc brakes will perform when combined with S-cam brakes on trailers, and trade cycles and vehicle residual value also should be considered. “In the end, fleets must look at the cost per mile over the expected life of ownership,” Kelley says.
But Plantan argues that for vehicles purchased after August 2011, front air disc brakes may be a good choice in terms of maintenance costs and procedures. “Those new vehicles are going to have a pretty beefy front brake that’s going to be doing its fair share of the work stopping the truck,” he says. “That is going to improve or reduce the amount of fade on long downgrades and also allow for cooler brakes, because the front brakes have much better airflow over them than the rear brakes do.”
Once the compatibility between tractor and trailer is optimized, the overall braking workload on the rear axles is reduced greatly. “We’re working very hard on that for both disc brakes, as well as some of the beefier drum brakes,” Plantan says. “So the extra cost that you’re putting in on the front brakes is actually saving wear and tear on the brakes on the rest of the vehicle.”
Both drum and disc brakes will work well when the new regulations come online in 2011.
The cost of switching
Brake manufacturers realize that higher acquisition costs for air disc brakes have convinced many fleets to stick with drum foundation brakes. Although prices may come down if more fleets switch to air disc brakes next year, they will remain a higher-cost item compared to drum brakes.
Also of Interest »