An expected change to federal stopping-distance regulations for trucks may not become effective until at least 2008. But that isn't stopping brake suppliers from moving ahead on the technological front to improve their products for truck buyers today, as well as tomorrow.

The consensus of brake engineers seems to be that truck fleet managers now enjoy the best of both worlds when it comes to spec'ing truck brakes. They can select drums or discs, or both, and they'll be sure of having proven stopping power.

Brake suppliers generally agree that drum brakes will be engineered to meet shorter stopping distances. But they also expect changing the regulation will give disc brakes a boost in the North American market. It may take a few years after the new reg hits, but as one engineer put it, “each type of brake will eventually rise to its natural level” of market acceptance.

The National Highway Traffic Safety Administration (NHTSA) has been considering reducing the mandated stopping distances for commercial vehicles for some time.

The first rule change will affect tractors. It is expected that the new reg will cut the current stopping-distance limit of 355 feet down by as much as 30%. That would mean tractor-trailers would have to stop in just 248 feet.

FUTURE THINKING

Trucking has been anticipating that NHTSA would issue a notice of proposed rulemaking by now, but as of press time it had not.

And given the speed of regulatory wheel spinning, whatever new stopping-distance limit NHTSA ultimately decrees won't become effective until 2008 at the earliest.

While that suggests any positive impact on highway safety is still a few years off, it also implies that brake suppliers and truck manufacturers have ample time to develop and engineer product to meet the expected new rule.

Discussions with OEM and brake engineers indicate that come 2008, the new rule will be handily met. They say by then fleets will be able to spec tractors either with what's generically referred to as “enhanced” or “wide” drum brakes or with versions of today's latest-generation disc brakes — or with the combination of discs up front, drums at the rear.

What's more, both drum and disc brakes will benefit from new friction materials being developed that will help improve braking performance and deliver longer life.

Regulatory action or not, the application of new technologies coupled with customer demand for lower cost of operation are ensuring brake developments are heating up.

Ken Bultemeier, heavy vehicle product engineer for International Truck and Engine Co., says truck OEMs pretty much expect “a front brake change will be required to meet the new stopping distance, as we understand it today.”

Based on the reasonable assumption that NHTSA's stopping-distance proposal notice will hew closely to what the industry is expecting, Bultemeier says the “current drum brake technologies available will be capable of meeting the proposed stopping distances. The added cost and weight of the required larger front [drum] brakes will make disc brakes more competitive.”

So, it won't be a matter of which brake type performs better. Rather, the new reg will help narrow the price differential between the two brake types, which may make disc brakes more appealing to a larger number of fleets that had avoided them previously strictly based on their acquisition cost.

Bultemeier points out that over the next few years truck OEMs will be engaged with brake suppliers to determine the best way to meet the new regulations for each given truck model.

“We are already working closely with our brake suppliers,” he states, “evaluating new technologies and field-testing various combinations including drums front and rear; disc in front and drums in the rear; and full disc brakes.”

Putting a finer point on the process, Bultemeier says that International's brake choice for ‘08 “will be the most cost-effective, most durable solution that meets the reg.”

In much the same vein, brake engineers who spoke with FLEET OWNER emphasized that product released to meet the expected ‘08 rule will be developed with more than an eye toward complying with a shorter stopping distance.

NOTICE DUE

“We expect to see an advanced notice or rulemaking coming from NHTSA by March,” advises Paul Johnston, ArvinMeritor's senior director - North American air foundation brake business. “So ‘08 is still a possibility, but realistically it could be ‘09 before the regulation takes effect. But in the meantime, there will continue to be improvements made to our brake offerings.

“To improve stopping distances,” he continues, “the industry has pretty much agreed we can put more braking power on the steer axle,” Johnston states. “Right now we underutilize the potential braking capability up front by 20% or more.” This, he notes, is essentially a legacy of the good old days when steer axles didn't have brakes.

Thankfully, today trucks come with front brakes and, Johnston points out, fleets can opt to spec “higher-performance” brakes up front, which he defines as being at least 16.5 ×5 in.

“We already have some fleets running larger drum brakes and they are seeing very good lining life, as well as greater stopping capacity,” he relates.

“For drum brakes, the engineering work is pretty much done to meet the expected regulation,” Johnston continues. “The shorter stopping distances will require switching to a less aggressive friction material [on larger drums] that will last longer on tractors” designed to meet the new reg.

“I think if it does end up being a 30% stopping-distance reduction for tractors,” he contends, “the all-drum solution may well prevail, depending, of course, on what OEM customers require.”

But don't count out air disc brakes. Johnston says the current generation being offered now coupled with the latest friction materials “definitely will meet” that 30% reduction.

“It is a very close race,” he notes. “Right now I'd say there is a 10 to 15 ft. difference in stopping capability between all discs [which still hold the advantage] compared to high-performance drum brakes.”

Johnston figures in the next few years some fleets may choose to run discs and drums on some vehicles to at least get more comfortable with discs. “Test after test, we have seen a measurable improvement from a disc-drum setup [vs. drums only].”

DISC ON DRUM

“The disc brake,” he continues, “is the most effective mechanical system, but there are other considerations, from installation to rotor life, that must be taken into account.”

An element to keep in mind when it comes to the disc-vs.-drum battle, according to Johnston, will be individual OEM preferences for brake types. “The S-cam brake is very flexible when it comes to being engineered onto the vehicle,” he explains. “The disc is not as flexible but that is less of an issue on the steer axle, where there is no suspension in place.”

He says another factor that could influence disc acceptance is whether there is concern over compatibility issues with the drum brakes found on almost all trailers. Were the industry to embrace full electronic braking (EBS), that concern would disappear.

However, EBS in North America remains stuck on a distant horizon. “ABS remains the right way to bring more features to the braking system,” Johnston remarks, “There will be a time for EBS but regulatory change will be needed and the customer will have to see that it would offer added value.”

At Bendix Spicer Foundation Brake LLC, Jim Clark, director of foundation drum brakes, and Ron Bailey, technical sales manager, concur that ‘08 looks like the time frame for the new stopping distance to become effective.

“We recognize there may be [brake choice] options coming out of this,” says Clark, “but it's too early to say what options OEMs will offer. We are seeing an evolutionary change happening. And that did not begin with an expected rulemaking. There are market pressures [influencing brake development].

“Wider, bigger drum brakes have been spec'd for a number of years now by fleets seeking both shorter stopping distances and lower lifetime costs. And air discs are becoming more widely available as more OEMs offer drums and discs or all discs.”

Clark stresses “the market will define brake choice — and there will be plenty of action in the next few years. You will see discs come on strong and seek their own level.” He says fleets know discs provide safety performance “and people are starting to see [service] life will be there with discs too.”

According to Clark, Paccar (parent of Kenworth and Peterbilt) is the “first to make use of the new ADB designs available to put disc brakes on a steer axle. That is a significant move in this marketplace and it may be followed.”

But he also points to the success of newer S-cam designs. “Some major fleets use our existing wide drum brake package to push brake relines right out of their trade cycles.” Clark says future “enhanced” drum brakes designed to meet shorter stopping distances will start with today's 16.5-in. models but boast linings that are more fade-resistant, as well as hardware items “tweaked” to ensure maximum performance. “Don't focus solely on the upcoming rulemaking,” Clark emphasizes.

Bailey says several factors will help boost ADB acceptance. “For one thing, a disc brake is a more complete package — there is no need for an automatic slack adjuster; the adjustment mechanism is built-in.

LINING UP

“Localizing disc brake production here,” he continues, “will help reduce the acquisition cost, as will volume production help economies of scale.” Bailey points out that Bendix Spicer will begin making its air disc brakes in Frankfort, KY, by the end of the first quarter.

Bailey says both disc and drum brakes will benefit from advances being made in friction materials. “For example, we are very high on transfer film technology as a means of improving both drum linings and disc pads.”

Russ Armer, president of friction material supplier Brake Pro, Ltd. confirms that high-tech developments are boosting the performance supplied by both drum linings and disc pads. He says Brake Pro uses three formulation concepts in one material — conformability, and transfer film/cohesive chemistry in a metallic fiber matrix.

“Transfer film technology, also known as cohesive friction, allows a fine layer of chemicals to be deposited on the drum surface and on the friction surface so that like material is rubbing on like material,” Armer explains. “The technology itself is not new. What we've done is combine that concept with an approach that makes the material more ‘conformable,’ that is to say, it beds into the drum a little more quickly thanks to a chemical structure that's slightly softer. Also, the metallic fiber matrix increases heat dissipation, allowing the brake to run cooler to improves wear and life.

“We can develop materials with a higher coefficient of friction with this combination of formulating concepts to provide a higher braking force,” he continues. “What you end up with is a material that boosts stopping power but lasts longer and is quieter when the brakes are applied. It's more expensive but provides better value over time.”

Armer says this product already has “wide acceptance in the severe-duty niche, such as refuse and construction trucks, where there is both high heat and heavy loads.”

He relates that Brake Pro has developed and begun marketing an expanded line of materials using what he calls the “conformable, cohesive, metallic” (CCM) approach. These friction materials will cover ratings from 20,000 to 29,000 lbs. Armer notes that while Brake Pro has developed these linings for drum brakes, the technology can be applied to disc pads as well.

PUSHED ALONG

According to Jason Oakley, product realization manager for performance Friction, which manufactures aftermarket heavy-duty disc pads, regulatory pressure in Europe is helping push along friction material advancements that will end up benefiting fleets here.

“In Europe, friction material suppliers are working to meet a tougher brake standard called Regulation 90 that will require higher performance at higher brake operating temperatures,” Oakley relates.

“We will be selling the new product under development for Europe here as soon as possible, both on the aftermarket and to OEMs, as early as this year's first quarter.”

Oakley says the new pad, to be marketed under the Carbon Metallic brand name, will be engineered to provide optimum performance at higher speeds. This is important because he says that once NHTSA issues its new stopping-distance rule, the agency may determine compliance based on brake performance testing at higher speeds than is now the case.

“If they raise the speed at which testing is done,” he says, “it will better reflect real-world conditions. The final standard will be tougher to meet, as higher speeds mean hotter brakes.”

From fleets demanding longer brake life to the government seeking shorter stopping distances, one thing is for sure. Brake engineers will be doing lots of stopping — and going — in the next few years.