What is a Performance-Based Brake Test?
 A Performance-Based Brake Test (PBBT) is any device which can quantitatively assess the braking performance of a vehicle. This is done through direct measurements of the brake forces at each wheel, axle or for the vehicle as a whole. Such devices include roller dynamometers, flat plate brake testers, breakaway torque brake testers and drawbar-type testers. Each of these devices can determine the brake forces without restriction to brake type (disk or drum) or energy supply (air, hydraulic or electric). In addition, PBBTs based on mechanical or electronic decelerometers can assess the overall vehicle braking capability through a stopping performance test in which deceleration and/or stopping distance is obtained, also independent of brake type or application method. Some PBBT types have been used worldwide for decades for both safety inspections and as part of regular Preventive Maintenance (PM) work in fleet shops.
What specific test results are obtained with a PBBT and how will these benefit my fleet?
A PBBT can provide wheel-by-wheel and axle-by-axle brake forces, which are important for:
Benchmarking – New vehicles’ brakes can be checked upon delivery to establish a baseline for future brake work or lining replacement selection.
Limiting Liability – Equipment providers can ensure that the vehicles they lease or rent have adequate braking capability before they are taken by the customer. Similarly, in drayage or other drive-away operations, trailers that are picked up can be checked prior to heading out.
Air System Problems – PBBTs have the capability to locate and identify problems within the air system. For example: a single brake with an early apply threshold can reduce lining life by two-thirds. Correcting such a problem can save $200 to $300 per axle per year.
Drum Problems – Out-of-round and off-center drums, affecting both brake wear and braking performance, can be found with a PBBT.
Parking Brake Problems – Broken or weak spring brakes can easily be identified with a PBBT.
Brake Balance – The brake forces at each wheel should optimally be in proportion to the loads on each wheel during a stop. Low brake force on one brake results in increased demand and accelerated wear on the other brakes.
GVW Check – Although not generally as accurate as certified scales most PBBTs have axle weighing capability.
Cargo Positioning - With additional information or estimations of weight shift during a stop, the effect of distribution as well as proper securement of cargo during a dynamic stop can be assessed.What other benefits are there for my fleet?
Increased Throughput – Every vehicle’s brakes can be checked in a matter of minutes before it leaves the yard, or for a motorcoach, before it goes into service for the day, providing peace of mind to the fleet operator.
Potential Savings on Insurance – Work with your insurer to determine whether your premiums can be lowered through the use of a PBBT. One fleet’s PBBT purchase was paid for in the first year through the reduction in premiums.
Lower Fuel Costs – Identifying dragging brakes or bad bearings can reduce fuel consumption.
Safety and Performance - Stopping distance, for which maximum braking capability is but one factor, can be enhanced through improved brake balance and increased overall maximum brake strength.
In my maintenance shop, can’t the same information be obtained from a complete brake inspection?
While some of the information available from a PBBT can be determined from a physical brake inspection, additional complementary information is obtained. In particular, no known visual inspection method can determine whether a given brake has adequate braking forces. Visual inspections can detect a potential lack of performance if certain components are missing, damaged or are out of adjustment. However, the actual brake performance depends not only on all components being present and in proper mechanical order, but particularly on the friction forces generated at the drum/block (or disk/pad) interface. In the case of some non-OEM aftermarket linings, contaminated or glazed linings and pressure restrictions in air lines, the braking performance can be dramatically degraded despite the proper appearance of all mechanical components. The use of the two complementary techniques is ideal for the maintenance shop.
Can’t I get the same information from a stopping distance test performed in my yard?
Not exactly. While stopping tests are the oldest quantitative method of determining overall vehicle performance, they provide limited information. The detailed brake force and balance information which helps a fleet keep its maintenance costs down are not available from a stopping distance test. Nor is any of the diagnostic air system information that can be determined with some PBBTs available from a stopping test.
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