This SAE Recommended Practice provides a field test procedure and instructions for: a. Instrumentation and Equipment b. Vehicle Preparation c. Test of air-braked single and combination vehicles d. Calculation of brake force distribution e. This test procedure is intended to be used as a field procedure. If a more refined method, utilizing laboratory equipment, is required, refer to SAE J1505. This code provides a method to determine the brake force distribution (brake system effectiveness) for commercial vehicles.