This SAE Recommended Practice establishes a method of testing the structural integrity of the brake system of all new trucks, buses, and combination vehicles designed for roadway use and falling in the following classifications: a. trucks and bus: Over 4500 kg (10 000 lb) gvwr and b. combination of vehicle: towing vehicle over 4500 kg 10 000 lb) gvwr. The test consists of two distinct tests: a structural endurance test followed by a structural ultimate strength test.