Disc v. drums
Performance? Cost? Maintenance? Durability? With the new braking standards trucks will certainly stop in shorter distances. But, are discs or drums the right answer for your trucking needs?

By Jami Jones, managing editor

New trucks are stopping nearly 100 feet shorter than the ones built before 2011, courtesy of a new braking standard issued by NHTSA.

The reduction in braking distances was a long time in coming, but eventually the National Highway Traffic Safety Administration issued a regulation in July 2009 that reduced stopping distances for heavy trucks by 30 percent.

The regulation mandates that trucks going 60 mph must be able to stop in 250 feet – down from the previously required 355 feet.

In response to the new standard, brake manufactures came up with a couple of options for truckers spec’ing new trucks: disc and drum. Those two options present their fair share of questions, however, for truckers needing to find the right fit for their operation in terms of performance, cost, maintenance and durability.

Air disc brakes win the head-to-head competition on stopping distances – but not necessarily by a lot. For instance, Meritor’s disc brakes stop shorter than even required by the new braking standard, but the Meritor Q plus RSD drum brakes also exceed the requirement by about 10 percent and can stop a truck within 10 feet of the air disc brake counterparts.

One key factor to consider when selecting a braking system is just how many stops, or braking events, happen in a “typical” day. For illustrative purposes, a truck in a local operation like a refuse hauler will stop more than a long-haul truck.

In that scenario, disc brakes can be more beneficial to a truck with more braking events on a daily basis. However, a coast-to-coast freight hauler with relatively few stops per day will generally find that drum brakes deliver excellent performance and reliability, according to Matt Creech, brake business manager for Meritor.

One misconception that continues to churn through the rumor mill in the industry is that drum brakes will add significant weight to the axles – to the point that truckers will be forced to reduce the payload weight. That’s simply not true.

Weight is not a major differentiator between the two technologies as the lightest weight specs for both are comparable, according to Creech.

So, head-to-head on performance and weight, the differences between air disc brakes and drum brakes for a long-haul operation are for all intents and purposes negligible.

Obviously, safety is always a top concern. You want your brakes to work when you need them. But now, with CSA in full swing, there is an added emphasis on long-term component reliability and maintenance.

The Federal Motor Carrier Safety Administration’s regulatory compliance measurement system called Comprehensive Safety Accountability, or CSA, ranks a motor carrier’s compliance with the vehicle maintenance regulations.

Compounding the pressure to have a “good score” is the demand to keep your truck running on down the road and not sitting behind a scale house with a big red out-of-service tag slapped on the window for faulty brakes.

The Commercial Vehicle Safety Alliance sets the out-of-service criteria for law enforcement. The criteria includes page after page after page of photos showing various brake conditions that will result in the truck being placed out-of-service.

This is one area in the disc v. drum head-to-head competition where a clear winner could be declared.

Air disc brakes certainly offer some advantages in this area, according to Creech. There is no required periodic lubrication schedule the way there is for a drum brake, and most of the required maintenance is periodic visual inspections only, he explained.

To make matters easier, Creech said that Meritor’s EX225 air disc brake has a visual pad wear indicator.

“This allows maintenance personnel or even the driver a simple, quick, easy-to-see method to check remaining pad lining volume without removing the wheel to measure the pad,” Creech said. “This saves a tremendous amount of time and negates the cost of purchasing additional lubricants for brakes.”

One more advantage is when it does come time to change the pads, the time required to change them is roughly 50 percent less than for drum linings once the wheel has been removed from the vehicle, according to Creech. On a typical tractor this can save almost three hours.

However, whether this delivers an overall life cycle savings really depends on the length of time you own your truck and how it’s used. Creech said with today’s upgraded drum brakes, the increased lining volume and good wear characteristics will often last the life of the first owner. Therefore, the savings in pad replacements aren’t realized.

Also, if a rotor needs to be replaced, then the length of time to service a disc brake tractor increases considerably. So as with all brake selections, it is a case-by-case evaluation.

Finally, cost.

Air disc brake systems do cost more than drum brakes. That said, Creech explained that the total cost of ownership benefits found with air disc brakes, CSA increasing maintenance and safety attention, and performance advantages in real world conditions should make the value proposition more attractive over time.

There will also continue to be technological advancements in drum brakes, making them a viable alternative to air disc brakes for some operations. They are not being abandoned by brake manufactures in favor of disc brakes. So, that option will remain.

In the end, selecting a braking system on your new truck will take careful evaluation of your braking needs weighed against the slight advantages and disadvantages of the two systems. LL