On August 1, 2011, a new air brake standard took effect for three-axle tractors with Gross Vehicle Weight Ratings (GVWRs) up to 59,600 lbs. This rule applies to tractors invoiced after that date. It will not impact any tractors you had in your fleet before August 1. But the regulation covers the vast majority of new tractors in use today.
The rule calls for a 30% reduction in the stopping distance from 60 mph vs. the previous standards. This means tractors must stop in less than 250 ft. from 60 mph when loaded to their GVWR and 235 ft. when lightly loaded. On August 1, 2013, heavier specialty tractors and lighter two-axle tractors will have to meet the standard. For a small number of very heavy severe-service tractors, the requirement will be 310 ft. under these same conditions.
Implications for straight trucks
This regulation was no surprise. It was finalized by the National Highway Traffic Safety Administration (NHTSA) in March 2007. OEMs have been working with suppliers to develop solutions, which include wider and more capable reduced stopping distance (RSD) drum and air disc brakes.
The regulation is intended to increase safety on public highways by reducing the disparity in braking between automobiles and tractor/trailer combinations. “Due to the nature of an on-highway tractor (80,000-lb. GCW), this regulation makes sense,” says Bernie LaBastide, Navistar chief engineer, brake systems. “It’s not clear at this point that the legislation would reduce collisions or fatalities for straight trucks. Straight truck environments are primarily city routes using slower speeds, etc.”
While straight trucks are exempt from the rule, there will be an impact as manufacturers take advantage of the new braking technologies. For example, Peterbilt announced it will make front-axle air disc brakes standard across its entire Class 8 truck and tractor line. For customers who prefer RSD drum brakes, there is that option, as well.
So expect to see some of the higher performance brakes start showing up on vocational straight trucks. “It only makes sense to use economies of scale by using the new and improved materials where applicable,” says Curtis Dorwart, vocational marketing product manager, Mack Trucks.
“My motto is ‘what is good for a tractor is certainly good for a truck,’” says LaBastide. “We currently offer not only bigger drum brakes, but disc brake options for straight trucks, as well. The benefits of larger drum brakes are more lining material and some reduced operating temperature due to the larger drum lining interface. Most linings react positively (reduced lining wear rate) with the reduced temperatures.”
He adds, “While not as popular as steer axle-only tractors, we do offer and sell all-wheel disc brakes on some straight truck models. Straight truck rear suspensions pose a distinct challenge to allow decent packaging for the air disc brakes. Thus, there is limited availability of air disc brakes on our straight trucks.”
Straight trucks can, however, continue using the standard brake configuration. “The previous brake lining material is still available for vehicles not affected by the new regulations,” says J. Allan Haggai, Daimler Trucks North America.
Bigger and better drums
The switch to RSD drum brakes or air disc brakes is relatively transparent.
“It was our desire to design brakes that were more capable and that would not send any specific signals to the drivers,” says Tom Runels, engineering manager for foundation drum brakes at Bendix Spicer Foundation Brake. “They can drive away and get no sense that there is anything significantly different underneath their vehicle. These brakes are much more capable, and in an emergency, they will be able to use that capability.”
The regulations required more than merely making the brakes larger. “To address the new braking standard, Mack made component changes to its standard drum brakes so they are more robust and generate more brake torque,” says Dorwart. “We’ve also introduced new friction materials on steer axles and some drive axles.”