One of the fundamental criteria of current and future truck safety technology development efforts – which includes electronic stability control (ESC), roll stability control (RSC), and assorted collision-mitigation systems – is that they must be “brake neutral” from the outset.
This means, according to manufacturers, that regardless of whether fleets spec their trucks with air disc brakes (ADBs), traditional drum brakes, wider drum brakes, or some combination of the above, there won’t be any degradation of safety system performance.
“There really is no direct correlation between the effectiveness of technologies like stability control and the types of brakes used on a particular truck,” Joe Kay, chief engineer-brake systems for Meritor Wabco, explained to Fleet Owner. “You’ll still get a small performance advantage with ADBs but they won’t significantly alter the capability of safety systems like ESC and others.”
“We don’t see [fleet] decisions concerning the adoption of certain safety systems driving the adoption of a particular brake package,” added Fred Andersky, director of government relations, Bendix Commercial Vehicle Systems LLC. “Those are really two separate decisions.”
That’s a critical point in light of the new stopping distance rules put in place by the National Highway Traffic Safety Administration (NHTSA) back in August of this year.
Those new rules require a typical three axle “tandem” tractor with a gross vehicle weight rating (GVWR) of 59,600 lbs. or less coupled to a trailer and traveling at 60 mph to come to a complete stop in 250 ft., compared to the former 355 ft. stopping standard — reducing tractor-trailer stopping distance roughly 30%.
For heavy, severe-service tractors with GVWs above 70,000 lbs., the stopping distance requirement will be reduced to 310 ft. at the same speed, with the caveat that all “heavy truck tractors” must stop within 235 ft. when loaded to what is termed their “lightly loaded vehicle weight” (LLVW).
Two-axle (4×2) tractors and tractors with a GVWR above 59,600 lbs. (6×4) must meet the 250-ft. at 60 mph rule by Aug. 1, 2013, with heavy, severe-service tractors sporting GVWs above 70,000 lbs. required to meet the shorter stopping distance of 310 ft.
Truck brake engineers emphasize that the majority of tractors – in this case those with tandem rear axles, which account for 60 to 70% of the highway rig population — can comply with the new stopping distance using nothing more exotic than wider “enhanced S-cam” 16.5-in. drum brakes that, due to their larger size and design refinements, dissipate heat more effectively and, as a result, help stop tractor-trailers in significantly shorter than their predecessors.
As a result, the decision on whether to adopt ADBs, stick with wider drum brakes, or spec an amalgam of the two boils down to cost, weight, and maintenance issues – not their performance characteristics within the broader scope of truck safety technology, Bendix’s Andersky explained.
“Safety technologies like ESC are designed to do what they have to do with the brake systems available today,” Meritor’s Kay pointed out. “Even the decision at the OEM level as to what brake system is selected depends on their engineering strategy and market view.”
The same feeling holds true in terms of brake control technologies as well, Bendix’s Andersky added.
“From our perspective, we really don’t see the North American market shifting away from air actuated brakes to electronically controlled braking systems (ECBS) for at least 10 to 15 years,” he notes. “The air brake system we have in place today is going to continue to be viable well into the future.”