The analysis of the behavior of a heavy truck brake system during deceleration is a complex undertaking.  It is important to first collect the physical dimensions and characteristics of the subject vehicle.  Those values, in conjunction with some approximations related to material properties and geometries, allow an investigator to use a series of equations and an iterative process to understand issues regarding an S-cam air-brake system.  The results of such an analysis can provide the average deceleration rate of the vehicle but also reveals information regarding braking effectiveness at each wheel which may be critical to an accident reconstruction analysis. 

GBF (Graphical Brake Force) is a computer program developed by Collision Engineering Associates, Inc. based on the research and data presented in SAE Paper 910126 by Ronald B. Heusser.  The equations and methodology have been integrated into an HVE-compatible program that accurately predicts an overall deceleration rate for an S-cam equipped vehicle as a function of braking effectiveness at each wheel.

The mechanical properties and dimensions of the braking equipment are used to calculate the braking torque at each wheel with respect to time.  This allows for the program to then compare the braking force available at the wheel to the available friction at the tire/road interface to determine whether the wheel will lock under the specific braking condition.  In addition, time dependent quantities such as temperature and dynamic stroke are included in the calculation method so that braking events of significant length can be accurately analyzed.

One of the current software requirements to use GBF is the EDC Brake Designer.  The parameters contained in the Brake Designer are required for the calculations in GBF.  When using GBF, there is no practical limit to the number of axles on the truck and trailer(s), however all of the brakes must be equipped with S-cam type brakes.

Contact Collision Engineering Associates, Inc. if you are interested in purchasing a license for GBF.