Showing posts from December, 2022

Coastdown Testing Revisited

  In my previous post about measuring changes in drag , I discounted coastdown testing as an unreliable method. I called it that because I had tried coastdowns several times and never got usable results. There were several reasons for this that I have been thinking about recently as I search for a method of measuring drag changes on my car. First, I was not good about keeping test parameters consistent; second, the tests themselves were not constructed properly; and third, I was trying to use the test results to calculate things (like drag coefficient) that relied too much on assumptions and were too small to reliably figure from this sort of testing on public roads, which naturally has high variability.   I decided to revisit coastdown testing and see if I could design and execute a test in such a way that the results could be trusted and could show me whether the aerodynamic drag of my car has changed. Here's how I did it, and how you can too.   Concept   The concept behind coast