Big change, bigger brakes

by John G. Smith

TAMPA, Fla. – New North American trucks will soon be required to stop more quickly than ever before, but manufacturers seem ready to meet the revised rules with the help of larger brake components.

In general, updated Federal Motor Vehicle Safety Standards are reducing a 6×4 tractor’s allowable stopping distance by 30%, requiring most loaded tractors to drop from 60 mph to a complete stop within 250 feet. Three-axle tractors with a Gross Vehicle Weight Rating of 59,600 lbs or less must meet the new rules by Aug. 1, while two-axle designs and those with a GVWR above 59,600 lbs will face the shorter distances by Aug. 1, 2013.

The reduction in stopping distances is even more dramatic than it might appear, said Bulkmatic’s Dennis Talentowski, during a recent panel discussion with the Technology and Maintenance Council (TMC).

“Most OEMs give you that 10% margin of error,” said the fleet maintenance director. That means the real stopping distances for a loaded tractor is closer to 225 feet. Passenger cars need to stop within 214 feet.

“That’s a lot of mass trying to stop very quickly,” he adds. “Our tractors will be stopping almost as well as the cars do.”
From an equipment standpoint, standard brake packages used to meet the pending rules seem to include larger brake linings, long-stroke brake chambers, and enhanced brake cams and bushings.

It should be little surprise that bigger components can translate into heavier weights. Each package will vary, but Navistar engineering manager Bernie LaBastide referred to one set-up with 16.5-inch friction material, Type 24 brake chambers and 5.5-inch slack adjusters that would add about 95 lbs to a vehicle.

“There is no one solution out there for every customer,” he said. Every trucker will have unique needs to be met, whether they focus on the initial cost of the components, brake life, maintenance needs or the ultimate weight.

While regulators are focusing on tractors in this ruling, many sources at TMC questioned whether the aggressive stopping power will lead to an imbalance in some braking systems, making it harder to keep a more lightly braked trailer in a straight line during a panic stop. At the very least, tractor brakes are expected to face some added stress because of their added work in every stop.

Computer modeling shows that there will be added torsional stress on the front suspension, noted LaBastide. And Mark Green, Peterbilt’s senior project engineer, referred to the way that vehicles with a shorter wheelbase could expect more of the brake-related load to be transferred to the front axle.

Some of the added stress and weights appears to be addressed with upgraded fasteners. Most 3/4-inch bolts have been replaced with 5/8-inch designs, and in selected cases there are even more fasteners being used.

“In the future, if you try to move brakes across the truck or put an old brake on a new truck, you may have an issue with different fastener sizes,” noted Anthony Moore, Daimler Trucks North America’s director of engineering responsible for brakes and pneumatics. “Don’t put 5/8-inch fasteners into 3/4-inch holes. That’s not going to work well for you.”

Linings are being upgraded as well. “You’re going to get brand new lining material – nothing you’ve ever seen before,” Moore says. “There will be some combination of organic and semi-met linings we haven’t used in the past.”

And there will be no time to rest. The latest reduction in stopping distances is likely a sign of tighter restrictions to come.
The National Highway Traffic Safety Administration (NHTSA) is actively researching a long list of technologies that could play a role in stopping vehicles.

“The best way to know what’s coming up in NHTSA rulemaking is to see what we’re doing in NHTSA research,” said the organization’s Alrik Svenson. In terms of avoiding crashes or reducing their impact, that research has meant a closer look at different stability controls, forward collision warning devices, and lane departure systems designed to keep trucks from straying out of their lane.

A focus on rear-end collisions includes research into equipment that warns about a pending forward crash, adaptive cruise control, “crash mitigation braking” that would automatically apply brakes, and other enhancements to the brakes. A uniquely Canadian rule has also caught the attention of US regulators who are studying our enhanced standards for stronger under-ride guards.

All of that may pale in comparison to the US Department of Transportation’s research into the possibility of a “connected vehicle environment,” where vehicles speak to each other with 5.9 GHz wireless signals. “The system can give a driver advisory, a driver warning, or in the next generation actually take control of the vehicle, similar to stability systems,” Svenson says. That has the potential of addressing eight in every 10 crashes among motorists who are not impaired. “There’s been a considerable amount of work being done on the light vehicle side,” he adds.

In the midst of it all, there will be a need to offset the changes that are introduced to reduce greenhouse gas emissions – creating brake-related challenges on their own. As rolling resistance is reduced in the name of fuel economy, for example, stopping power will need to be adjusted.

“Anything that lowers the rolling resistance will increase the effort that has to be generated somewhere,” Moore explains. “We’re going to have to, correspondingly, somehow, improve the braking capabilities of the vehicle.”

The design of a tire’s tread, the related material, carcass design, inflation pressures and profile all have a role to play in stopping distance. Harder, high-mileage tires may present a problem when trying to build systems that meet the new rules.

“Heavy-duty truck tires are currently a bit of a wild card,” explained Vince Lindley, director of warranty, quality and reliability for Volvo Trucks North America. “There is currently no industry standard traction rating.”

Yet another factor could add to the strain on brake components. The growing interest in stability control systems could also require brakes to be applied during a larger percentage of their time on the road. “That will increase the work we put into the brakes,” Moore says.

Think that’s the end of it? Don’t forget other environmental regulations. Pushes to eliminate the copper in brake linings will likely lead to further changes in the lining materials used in the next five to 10 years, Moore adds.

It appears that regulators show no sign of slowing down.

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