The difference between stopping in 310 feet and stopping in 225 feet is five car lengths. So says Frank Gilboy, product manager for wheel end components at Bendix Commercial Vehicle Systems.
The reduced stopping distance now required for new trucks coming off the production line is 225 feet. And the 310 feet is the stopping distance a truck achieved when Bendix changed RSD friction material to a pre-RSD aftermarket friction material during a stopping distance test.
One of the first things to remember about the RSD regs is that they only apply to new trucks, which regulators wanted to make sure “were able to stop a little quicker and sooner in traffic,” says Pete Freeman, senior product manager at Meritor.
A variety of changes occurred to the braking system in order to meet the RSD requirements.
“Increasing the size of the steer axle brakes from a 15-inch drum diameter and 4-inch-wide brake to the RSD configuration of 16.5 x 5 inches did not provide enough stopping power to meet the 250-foot requirement,” explains Dennis Griffin, product manager, commercial vehicle friction for Federal-Mogul Motorparts. “Consequently OE brake engineers commissioned friction manufacturers to design new high-performance materials. It took the combination of bigger and better brakes to meet the RSD standard.”
Where once it was a matter of looking at how much torque the brakes could put out — 20,000 pounds or 23,000 pounds — now the concern is how the friction material acts throughout the entire stop. “You can’t have friction that fades,” Gilboy says.
Brake lining manufacturers put together a combination of metallic friction and organic friction to maintain more torque throughout the entire stop.
New trucks now are doing a better job of stopping in a shorter distance. And since most fleets are concerned about safety, many are opting to continue using RSD friction at lining replacement.
Here’s where the confusion comes in.
There is no requirement that aftermarket linings meet reduced-stopping-distance requirements. According to Griffin, that means replacing RSD brakes with RSD brakes, while not mandated, “is a common-sense best maintenance practice.”
However, it might not be readily apparent that a particular friction material actually meets the RSD rules. Gilboy says there are only two ways for RSD friction to be validated. One is by the truck OEMs and the other is via independent third-party testing, both of which rely on FMVSS 121 vehicle testing.
John Thompson, sales manager, OE at TMD Friction, explains that OE friction manufacturers clearly state in their product portfolio the materials that are RSD.
“Care must be taken by fleets when selecting [replacement friction material] as there are aftermarket-only friction manufacturers claiming to have RSD material,” he says. “This can only be true if their friction products are installed at the factory by the manufacturer.” Or if they have been tested by an independent third party using on-vehicle testing.
So how do you ensure that you are getting RSD friction material if you buy from an aftermarket only supplier?
Be wary of suppliers who provide you with test results based solely on dynamometer testing, Freeman says. “And be suspicious if you are told that a friction material you have been buying for years is suddenly an RSD material. Ask the supplier for the names of the OEMs that are installing their friction as well as results from tests that show the brakes are RSD-compliant.”
The impact of not selecting the right friction material could be as little as five car lengths.