The National Highway Traffic Safety Administration likely will finalize its rule establishing a shorter stopping distance by this fall, and implementation could come as soon as 2009, experts say. The new standard – which, like the current one, will involve the braking of the tractor only, tested with a loaded but unbraked trailer behind – could mean the stopping distance will be 30 percent shorter than before.
Today, cars traveling 60 mph stop in 150 to 170 feet, and trucks in about 300 feet. After the change, the distance for trucks will be 230 to 240 feet, which will be “a tremendous improvement,” says Randy Petrish, vice president of technical services at Haldex. That’s because when it comes to truck-car collisions, closing speed and stopping distance are major worries, Petrish says. Bendix Spicer Foundation Brake officials report that NHTSA’s proposal actually calls for a 20 to 30 percent reduction, but the company strongly supports the full 30 percent reduction.
Will this require a revolution in tractor braking systems? Not at all – at least not on twin screw tractors, says Petrish, who explains that some fleets already spec brakes that can do the job. The biggest change will be upgrading front-axle brakes from today’s standard-size 15-inch-diameter drum and 4-inch-wide lining to 16.5 and 5 inches, respectively.
Those brakes will produce double the torque of today’s front-axle brakes, says Paul Johnston, Meritor WABCO’s senior director of compressor and braking. And without criticizing the industry for sticking with 15-by-4 front-axle brakes, Petrish believes this is an overdue change.
What many fleet maintenance managers may not realize is that such a change might not only reduce the company’s safety liability, but also have a favorable overall cost impact by cutting the number of relines needed over a tractor’s life cycle. The change on the front axle would increase the lining volume of a Meritor Q Plus brake from 46 cubic inches to 76 – a 65 percent increase. The drive-axle brake size increase would produce a 24 percent increase in lining volume.
Of course, tractors with single drive axles are likely to need more than better front-axle brakes. “Customers need to be careful not to upset the brake balance between tractor and trailer,” Johnston says. “Trailers are not included in the regulation changes, and there are a lot of existing trailers in the field with current brake systems that will be used with the new tractors.”
The next step in improving front-axle braking would be disc brakes, which Petrish believes are superior in every respect. “There are maintenance advantages because of longer lining life, and they eliminate pull because drums are self-energizing, something that cannot be controlled, while discs are not,” Petrish says. “They offer superior uniformity, consistency and repeatability.” Discs offer the same stopping power throughout the lining’s life, whether hot or cold, which helps balanced braking, Petrish says.
