Enhanced Braking

New federal braking regulations for heavy trucks

The new upgraded steer axle brakes will now approach the performance capability of a rear brake, says Ron Plantan, principal engineer, Elyria wheel-end group of Bendix Spicer Foundation Brake. In some applications, because the front brake can be doing more work, that work is distributed over more axles.

"There's an opportunity for longer life if everything is optimized across all axles of a combination vehicle," he says.

With the larger drum and disc brakes maintenance costs should go down, says Pennington. Larger brakes will provide such advantages as increased lining volume to drive longer service intervals, lower operating temperatures, reduced fade and improved performance.

Air disc brakes are internally adjusted and factory-greased so there is reduced maintenance required, he adds. Air disc brakes also have fewer parts to replace, all of which helps reduce unscheduled service requirements.


Tractor and trailer braking system balance will not be affected. The air systems will be balanced like they are today, with no need for pressure hold-off valves or changing chambers, etc., to get compatibility among tractor and trailer brakes systems, says Meritor WABCO's Johnston. However, there may be some algorithm changes on ABS systems because of the performance difference.

The tractor will incur a little more of the braking workload, which will have some impact on the front axle and suspension components, he says. The trailer, meantime, will experience a proportionate reduction in workload.

Another thing that fleets need to be aware of: With trucks that can stop in shorter distances, more attention must be paid to properly securing cargo, says Eberling of Bendix Commercial Vehicle Systems.


The cost of the new regulations, according to the NHTSA's assessment, is that new enhanced foundation drum brakes on a typical three-axle Class 8 tractor will add about $200 to the cost of the vehicle. Having an all-wheel air disc brake solution will add $1,400 to $1,500 to the cost compared to the current baseline vehicles.

NHTSA has justified the added cost by estimating that the new FMVSS 121 will prevent more than 200 deaths and 300 serious injuries each year, plus reduce property damage costs by around $170 million annually.

Brake manufacturers are always working to deliver brake system solutions that help keep the cost of operation in check, Plantan says. "But it is fair to say that there will be a nominal cost increase for new trucks and aftermarket parts.

"What is important to remember, is that if the system is optimized, the end-user will see added value because of it. If the customer keeps the vehicle three to four years, they will likely break even, depending on what choices were made."

Furthermore, he says some options that Bendix Spicer Foundation Brake has been monitoring out in the field - such as the larger diameter and wider drum brake packages and air disc brake packages, for example - "have in some cases actually doubled the life of the braking systems."


Performance-based brake testers (PBBT), used for decades for safety inspections and as part of regular preventative maintenance work, are not going to be affected by FMVSS 121. These machines assess the braking capability of a vehicle through a quantitative measure of both individual brake and overall vehicle performance in a controlled test, done through direct measurements of the brake forces at each wheel end, axle or for the entire vehicle.

PBBTs include roller dynamometers and flat plate brake testers. Each of these devices can determine the brake forces without restriction to the brake type (disc vs. drum) or energy supply (air, hydraulic or electric). PBBTs based on mechanical or electronic decelerometers can assess the overall vehicle braking capability through a stopping performance test in which deceleration and/or stopping distance is obtained, also independent of brake type or application method.

PBBTs have been used worldwide for decades for both safety inspections and as part of regular preventative maintenance work.

As of Feb. 5, 2003, section 393.52 of the Federal Motor Carrier Safety Regulations was amended such that certain PBBTs can be used for enforcement of minimum braking performance requirements on commercial motor vehicles. The Commercial Vehicle Safety Alliance (CVSA) approved PBBT-based out-of-service criteria for roadside enforcement officials effective throughout North America on April 1, 2008.

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