Hi,
Here's the "Instructables" page that I used:
Equipment
I highly recommend a point-and-shoot digital camera that can do video for about 1 1/2 minutes or more -- go a little above 70kph (or convert the spreadsheet to mph) and start the video, put it in nuetral and coast for 70 seconds after you hit 70kph. Do three passes in each direction, and then watch the videos, and note the time you hit 70kph, then pause the video every 10 seconds after that, and enter the speed in the spreadsheet.
The trick with this is to get a relatively accurate frontal area, and you'll still have to make your best guesstimate of the tire rolling resistance -- this is really tricky, because a very small change in RR makes a rather large difference in the Cd.