Discs or Drums?

That Is a Fleet’s Question
Bendix collision mitigation
Bendix offers collision mitigation braking. (Bendix)

Not all fleets are convinced of the benefits of air disc brakes. But suppliers maintain there is a growing acceptance of them for heavy-duty trucks, driven by an increase in the deployment of active safety technology, such as collision mitigation and avoidance systems.

Fleets’ perspectives run the gamut from, “We love them,” as stated by ­David Stevenson, president of Gilmer, Texas-­based Custom Commodities Transport, to “We have not extensively looked [into air disc brakes]” in the case of Dan Deppeler, vice president of maintenance at Paper Transport Inc. The company wants to see better economics first, he said, noting the upfront cost for ADBs is significant.

Many variations of those two opposing opinions are out there.

In the case of Hirschbach Motor Lines, where the trucks had been spec’ed with disc brakes at every wheel position — including trailers — the company has reverted to spec’ing drum brakes on the drive axles. However, it is continuing with ADBs on the steer axle of the ­newer tractors, said John Vesey, the fleet’s operations support manager.

The main reason the company went to ADBs was due to advances in disc brake and vehicle design that resulted in weight savings over drum brakes available several years ago, he said. Now he is spec’ing a lightweight steel jacketed brake drum.

“It’s pretty much a neutral weight decision,” Vesey said. “We looked at cost and we realized the benefit of the disc brake on drive axles wasn’t really there for us.”

The drive axle disc brakes were plagued with high rotor wear, necessitating rotor replacements that reduced any maintenance savings, he said.

Kirk Altrichter, vice president of fleet services at Kenan Advantage Group, mostly a tank operation, also had problems with early disc brake designs. He only recently came around to spec’ing ADBs — first on trailers and now on steer axles. Altrichter remains on the fence for drive axles.

A Wabco Maxxus caliper on a mounting plate. (Wabco)

“I moved everything over last year on trailers, and I moved the steer axle to ADB this year,” Altrichter said.

There were weight and cost penalties with early ADBs, but much of that has been eliminated, said Altrichter, who spoke about disc and drum brakes during the Technology & Maintenance Council’s annual meeting earlier this year.

“We have had issues with pads chunking or wearing unevenly that meant we had to work on the disc brakes more often than the drums,” he added. “So savings is in question.”

Jon Morrison, president for the Americas at Wabco Holdings Inc., said he was surprised to hear about some fleets’ caution on spec’ing drive axle ADBs.

“We do see ADB moving into more general applications,” he said, noting that with Wabco’s Maxxus brake, “we haven’t had any re-conversions. Once a fleet goes to discs, they stay with discs.”

With the purchase of Meritor’s share in the Meritor-Wabco joint venture late last year, Wabco has invested heavily in a field service team to address problems early and find solutions, he said.

“It’s something we monitor very ­closely. We haven’t had any customers revert back,” Morrison said, noting that moving to ADBs is an important decision.

“Weight is one concern and we’ve been able to reduce the cost and work with the OEMs to optimize the configuration of the wheel-ends for disc brakes,” he said, noting this helps with overall performance and acceptance.

Air disc brakes are part of Ploger Transportation's drive for better fuel economy as well as improved safety. (Ploger Transportation)

Chris Villavarayan, senior vice president at Meritor Inc. and president of the supplier’s global truck business, said fleets are starting to see the benefits of ADBs, “especially in safety and performance. We have validated the EX+ [ADBs] in the most severe conditions to deliver superior performance and lower life cycle costs.”

Also, Meritor’s ADBs are compatible with most collision mitigation systems currently on the market, he said.

This is a consideration for Kenan Advantage’s Altrichter.

“Over time, I see a blending of safety systems and ADB,” he said. “Everything of ours over the last four or five years has been spec’ed with Bendix Wingman — Advanced and Fusion — all work in conjunction with one another.”

Keith McComsey, director of marketing and customer solutions for wheel-end at Bendix Spicer Foundation Brake, said safety is among the key benefits of ADBs. “Shorter stopping distances, virtual elimination of brake fade, and improved in-line brake stability (from left to right side) providing surer, safer stops, make air disc brakes an improvement in safety over drum brakes,” he said.

In testing using the Bendix air disc brake system, ADB22X, at every wheel-position on both the tractor and trailer at 80,000-pound GCW, “we’ve demonstrated approximately 20 foot shorter stopping distance at 60-mph,” McComsey said.

Similar to the other players that make ADBs, Haldex sees a major shift in heavy-duty braking on the horizon.

“The safety systems can utilize the performance characteristic of the disc brake much more effectively than they can with the drum brake,” said Paul Chappell, Haldex’s product manager for ADB. “Not only are you picking up the disc brakes but you’re increasing the benefits from collision mitigation.”

Disc brakes, Wabco’s Morrison added, no longer impact used value at trade time and keep the promise of low cost of ownership.

“When we look at ADB performance — and it depends on the application — the large truckload fleets, for example, are seeing that it is feasible to get through their trade cycle without having to service the brakes as they are seeing good lining life and performance. And we now see it’s not affecting trade-in values, so it’s not a deterrent for future trades and that’s also helping acceptance and getting more fleets on board.”

ADBs provide “very tangible benefits regarding total cost of ownership,” Bendix’s McComsey said. “Consider the potential cost impact to having shorter stopping distances, and reducing your risk for an accident or mitigating the total cost of an accident. An accident that used to cause property damage and injury, could potentially be reduced to property damage only or even become a ‘near-miss’ situation.”

“Couple that with all of the maintenance and reduced downtime opportunities and your lifetime cost or Total Cost of Ownership (TCO) can be much lower," he said.

Over time, I see a blending of safety systems and [air disc brakes].

Kirk Altrichter, Kenan Advantage Group

At Ploger Transportation, disc brakes are part of the fleet’s drive for fuel economy.

“We’re learning more and more,” said Joel Morrow, Ploger’s vice president of equipment procurement, who also is a driver for the family-owned fleet. “We’re big into the 6x2 liftable axle trucks and liftable axle trailers and as we lift axles off the ground, our braking capacity goes down,” Morrow said. “The disc brakes are a nice way to balance out our braking needs when we’re running axle-up with payload on the trailer.”

“[The drivers] are very confident with the disc brakes, knowing the truck’s going to stop with axles up and it feels right to them,” Morrow said. “So, in a roundabout way, they help us get better fuel economy.”

However, Morrow sees braking performance as the prime reason for choosing ADBs. “Safety is our absolute priority. That’s why we spec disc brakes.”

According to Haldex’s Chappell, market penetration for ADBs will reach 50% by 2020 to 2021. That’s when the company will introduce a single-piston tractor disc brake engineered for the North American market, he said.

For specialty suspension manu­facturer Reyco Granning, safety was an important factor in designing an independent front suspension, or IFS, for fire trucks and recreational vehicles. “One of the first products we incorporated ADB on was a motorhome IFS rated at 16,600 pounds,” said John Hinz, chief engineer for powered vehicles.

The company’s first IFS units were built for drum brakes, but its customers ultimately requested disc brakes for safety reasons, he said.

“They didn’t like the brake fade of drums,” Hinz said. “In the motorhome market, you have a lot of inexperienced drivers who don’t have CDLs. When you’re going down the side of a mountain, it’s better to have disc brakes instead of drum brakes, as disc brakes will go and go without brake fade.”

Most of Reyco Granning’s IFSs come with the Bendix ADB22X but stepping up to Bendix’s higher capacity SN7 disc brake has allowed the company to engineer a fire-truck suspension with a 24,000-pound front axle rating, showing the capability of the disc brake in demanding applications.

This capability of the ADB is attractive to Custom Commodities Transport’s Stevenson. “We do liquid and dry bulk, and we’re very satisfied with air disc brakes,” he said, adding their ease of maintenance also works well for the fleet’s truck technicians.

ADBs allow the company to be more responsive with drivers who are “not so attentive or there’s human error from the general motoring public,” Stevenson said.

Meanwhile, Bendix’s McComsey said ADBs offer less downtime. They “provide extended service intervals for friction replacement to the point where some fleets may be able to avoid a friction change prior to trading out their vehicles,” he said, adding that if they do have to make a friction change, it can be completed in roughly one-quarter of the time versus a drum friction change, which reduces maintenance labor costs.

However, Paper Transport’s Dep­peler said the maintenance savings with ADBs are not as material as the manufacturers say. “The frequency of rotor replacements ruins the economics.”


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