It would be difficult to deny the benefits that emerge with the use of air disc brakes. When compared to the widely used S-cam and drum brake systems, the compressing forces of a disc will provide shorter stopping distances, brake applications tend to be more balanced and old friction material usually can be replaced in a fraction of the time.
Most of the worries about brake fade also, well, fade away. Unlike a hot drum that can expand beyond the reach of its friction material, a disc brake’s hot rotors will expand toward the pads.
An increasing number of buyers are “definitely intrigued” by the designs, says Neil Shroff, vice president of business development for DuraBrake, which distributes related components from a variety of suppliers.
Intrigued they may be, but the industry’s buyers have been slow to adopt the equipment. While air disc brakes were first introduced for North America’s trucking industry in the 1980s, they barely account for one percent of the annual brake market’s 2.4 million wheel ends, says Paul Johnston, ArvinMeritor’s senior director, compression and braking. Even when they are purchased, the brakes are largely limited to rescue vehicles, motor coaches, specialty equipment and fleets that want to experiment with the related components.
CHANGE AHEAD?
But we are only a few months away from a decision that could support the wider use of air disc brakes.
The National Highway Traffic Safety Administration (NHTSA) is expected to reduce minimum stopping distances by as much as 30 percent, despite industry lobbying efforts to limit such reductions to 25 percent, explains Aaron Schwass, director of air disc brakes at Bendix Commercial Vehicle Systems. This means a typical 56,470-pound GVW tractor and a non-braked trailer might need to drop from 60 mph to a complete stop within 250 feet. And while most of today’s vehicles still could meet these reduced distances by using larger drum brakes, there are exceptions.
The need for disc brakes could come down to factors that include Gross Axle Weight Ratings, suspension ratings and a vehicle’s wheelbase, explains Randy Petresh, vice president of technical services at Haldex Commercial Vehicle Systems. “Wheelbase is a huge factor in terms of determining dynamic weight transfer.”
