Brake System Calculations

Below is a frame grab of an Excel spreadsheet I created to calculate the stopping distance of a Mk IV Roadster based on the braking system configuration.  The spreadsheet should be easy to reproduce as there are no hidden functions. The calculations are based on the discussion in Walker (2007); cited below.  It is an excellent introduction to braking. A link to the actual working spreadsheet for downloading is here: Linked Excel spreadsheet. Parameter dimensions are indicated.  [--] indicates 'dimensionless', e.g., in./in.; ^ (a ‘carrot') indicates the parameter is raised to that power (e.g., ^2 means squared); * indicates multiplication; / means divided by.  Note: this is just a ‘model’ of braking behavior.  The algorithms (i.e., calculation steps) are verified, i.e., the Excel calculation steps returns the expected value (i.e., I checked the ‘brake force’ calculation (line 21) with my calculator and the results match).  However, the overall model has not been validated for an actual Factory Five car, that is, I don’t really know how the calculated braking distances compare to the actual braking distance of a car.  So, the best use of this model is to use it to understand how the different components of the braking system affect braking and which factor might have the greatest influence when modifying the braking system on your car.

A way to think about braking systems is this (from Speed Secrets: Winning Autocross Techniques by Ross Bentley):

The braking system on most cars is more powerful that any other system in the car.  In other words, the car is capable of stopping much more quickly than it can accelerate. [When racing] take full advantage of this.


The model input parameters (i.e., A6 to A19), although roughly approximate for the Mk IV, are meant to serve for the example calculations, not be an accurate representation of the actual input parameters that will be required for a specific vehicle.