Buyers to Have More Brake Choices
This story appears in the Sept. 21 print edition of Transport Topics.
RALEIGH, N.C. — The federal stopping-distance rule announced in late July will generate lots of technical choices for truck buyers, but manufacturing executives told fleet managers here the engineering changes should be minimally disruptive.
Brake makers and one truck maker told maintenance directors that devotees of drum brakes should be able to keep them if they do not want to switch to more expensive air disc brakes. However, the new drum systems will be larger and heavier, and engineers are wrestling with the problem of which friction materials should be used.
The manufacturers’ Sept. 14 briefing was part of the fall meeting of the Technology & Maintenance Council, a unit of American Trucking Associations.
“The production of this rule surpassed elephant gestation [of 22 months],” said Mac Whittemore, Midwest regional manager for brake maker ArvinMeritor Inc.
The National Highway Traffic Safety Administration formally started work on updating the stopping distance rule in 2005. On July 24, the agency said tractors traveling at 60 mph would need to be able to stop in no more than 250 feet, a 30% decrease from the current standard of 355 feet (8-3, p. 2). For most tractors the rule will take effect in August 2011.
Whittemore and Jim Clark, director of global wheel-end programs for Bendix Spicer Foundation Brakes, said the physics of stopping means the steer axle brakes will have to do a lot more work. When a moving vehicle stops, weight is transferred forward, creating front-end nose dive.
Whittemore laid out a menu of incremental options for dealing with the challenge. Providing the least extra cost, but also providing the least improvement in stopping distance, would be spec’ing a new truck with larger drum brakes with more aggressive friction material.
The next option would be putting disc brakes on the steer axle but keeping drum brakes on the two drive axles. The most costly option — but also the one that shortens stopping distance the most — is using discs on all three tractor axles, Whittemore said.
Fleets hauling heavy payloads might want to consider disc brakes, said Vince Lindley, manager of national account fleet service for Volvo Trucks North America, because the new, larger drum systems also will be heavier.
Lindley said managers of each trucking company should sit down and decide what is most important among performance, weight, initial cost, maintenance cost, durability and compatibility with other tractors.
Whittemore said that planning then would serve as the basis of discussion among fleets, truck makers and component suppliers.
The manufacturers also spoke of two side benefits and one challenge related to the rule change.
Whittemore said the new rule addresses panic stopping from 60 mph, which is important but not typical. In more common operation, the extra unused capacity could lead to increased brake life, he said, speculating.
Also, because the standard refers only to tractor brakes, it does not reflect the real world where trailers have brakes, too.
Brake engineer Tom Rogers, a colleague of Whittemore’s at ArvinMeritor, said in an August interview that if a tractor can stop a loaded rig in less than 250 feet, the real stopping distance with trailer brakes might be 180 feet to 200 feet. Rogers and Whittemore both said tractor and trailer brakes should be balanced, so that the braking task is shared between them.
The challenge, Whittemore said, will be with friction materials. The more aggressive the material, he said, the more likely it is to cannibalize the drum components that contain it. Engineers have not yet figured out how to produce greater stopping power along with strong durability, he said, although they have until August 2011 to work on the problem.
