That same report bluntly states that the FMVSS 121 testing of small lining samples "is not considered accurate in determining performance on a full size brake," making it abundantly clear that this particular procedure is no longer a reliable barometer of how a brake should perform in today's RSD environment.
The 96' Difference
Using sophisticated vehicle performance testing systems, Bendix compared the 60 mph stopping distance of an RSD-compliant vehicle with OEM high-performance brakes and linings against both pre-RSD original equipment and off-the-shelf aftermarket linings. Despite passing the FMVSS 121 dyno test, neither the pre-RSD OEM friction nor the aftermarket replacement friction met the new 250' RSD requirement.
In fact, when equipped with a popular "20K" (20,000-lb rated) aftermarket friction, the vehicle's stopping distance increased from 215' using the high-performance OEM friction to 311', a stunning 45 percent decrease in performance. That 96' difference in stopping distance, the approximate length of five passenger cars, is a stark illustration of the roadway safety at stake.
It's also worth noting that at 215', the stopping distance for the OEM high-performance friction is 35' below the RSD requirement, demonstrating its ability to far exceed RSD standards.
Because there is no practical "on-the-road regulatory test" of brakes in action, however, drivers of vehicles using aftermarket replacement friction won't know whether their new linings have compromised their stopping power until a real-world situation is at hand. An emergency stop is no time to find out.
The safety concerns associated with substandard aftermarket replacement friction are real.
When the time comes to replace brake linings, fleet owners and operators are best served by relining with high-performance OEM friction. By doing so, they can ensure RSD-level braking performance and enhance highway safety.
Conclusions drawn from Bendix stopping-distance testing and analysis.