Air Disc Brakes
They offer safety and maintenance advantages, one fleet finds.
Tom Berg
Senior Equipment Editor
Air disc brakes have not exactly been selling like hot cakes, even if they might just be the next best thing since sliced bread.
Metaphors aside, discs for heavy duty trucks have been around for more than 30 years, but false starts with these high-power stopping products gave them a bad reputation. With some, that rep remains – even though it is no longer deserved – and their extra upfront cost doesn't help.
So fleet people have grown skeptical. They also know that modern drum brakes are entirely adequate for everyday driving conditions, and that they meet government-mandated stopping limits for heavy trucks.
So why pay extra for something else?
"To stay ahead of the curve," answers Bruce Stockton, vice president of operations at Contract Freighters Inc., in Joplin, Mo., which has been ordering ADBs on new road tractors for more than a year. "We figure that discs will be required in a few years, and wanted to get familiar with them."
Fleet people who wait until a mandate takes effect will have to learn fast what effects the new brakes will have, and might have a tougher time.
A mandate is likely to come in the form of reduced stopping limits for heavy trucks that only air disc brakes can meet. The government hasn't said what it's considering, but supplier people believe that stopping distances will be cut by about 30 percent. That would reduce the present limit of 355 feet at 60 miles per hour to 248.5 feet at the same speed.
This would bring heavy trucks much closer to the performance of smaller, lighter vehicles, which must halt after about 200 feet. And the new regs are likely to require specified performance at higher speeds, because many states allow heavy trucks to go 65 to 75 mph.
CFI now has about 1,100 Kenworth T600 and T2000 road tractors with Dana Spicer steer-axle ADBs. Stockton says they are safer, and that reduced maintenance will pay for their extra upfront cost. CFI would order discs on drive axles, too, but KW doesn't yet offer them there.
"There's no doubt that they stop quicker," Stockton says of air discs, noting that both he and Glenn Brown, CFI's chairman, drove a disc-equipped tractor that CFI tested for three years as part of its plans to adopt the new brakes. "We feel this has been reflected in our reduced accident rate. It's hard to put numbers on it, but we've seen fewer incidents and think the discs have something to do with it."
Discs are part of CFI's overall approach to safety, Stockton says. That drive for safety includes background checks on driver applicants, which the fleet began in 1982 – nine years before the government required them – as well as initial and recurrent training for drivers. He believes driver training will become even more important as drivers get used to more powerful brakes and begin overdriving – following too close to traffic ahead because they think their brakes will make up for it. That's what happened with a collision avoidance device that CFI tested, and for that reason does not now buy.
Discs do save maintenance money, according to experience so far, he says. Pads and rotors on the Spicer ESD225 discs should last more than the fleet's anticipated life cycle, which is 400,000 to 500,000 miles. That means that a reline usually done with drum brakes will not be needed with the ADBs, and the parts and labor saved should offset the upcharge for the option.
That's partly because CFI is paying less than Kenworth's usual selling price of about $700 for the steer-axle-only brakes. Other fleets probably could buy them for less, too.
Although ADBs are now standard on some fire trucks and motor homes, they are not readily available on Class 8 commercial trucks. Those who do offer discs will install them only on highway tractors, and they can weigh more than drums unless they're spec'd with aluminum hubs.
Manufacturers do report more interest in ADBs, with truck operators asking about them at trade shows and such, but few actually spec them. Fewer than 5 percent of Class 8 trucks are now built with discs, and that includes the specialty vehicles. At Kenworth they are a regular production option, but that's not the case with every builder, and buyers may have to ask if they're among a builder's unpublished options.
But as CFI's experience indicates, the extra effort might be worth it.
