Calculating Drag

I found some interesting information on how to calculate drag without a wind tunnel. This looks like a really good measure and will calculate every bit of drag including rolling resistance.

Basically you measure how fast your scooter will slow down to 95 Km/hr when you pull the clutch in at 105Km/hr. Without brakes, the only thing slowing you down is drag, so knowing how fast you slow down tells you how much drag you have.

I'll do the sums, give it a go and then write a simplified lab page on how to test.

How can I measure the drag on a car?