I was trying to measure my rolling resistance and coefficient of drag by performing coast down tests. The typical technique is to try to time when you slow down from 60 to 50 to 40mph etc. Some people recommend that you have a person sit next to you and record the information, and some people use a video camera aimed at the speedometer. I decided to try my wife’s GPS running watch to record the data. These watches record a runner’s route so they can tell if they’re improving the times. The GPS running watch I used records data every second. I was able to simply drive up to speed and coast down. Then go home and dump the data. This is a little tricky dumping the data. I have written some articles about this on my site, and there are some spreadsheets that help calculate Cd and energy use for you recorded route. I hope others can use this idea to get better estimates of their car’s Cd. My site is [
www.electricmgmidget.com] .After looking this over, if you have any questions, please feel free to ask.