Double clutching isn't only used in downshifting. As a matter of fact...I've never heard it used in that sense. Double clutching (the way I do it) is used when racing in a straight line. Its simple...when racing either off the line or when you are alerady on the highway(you won't feel as much when you are going fast)is when you are at about 3500 or 4000 rpms, you pop the clutch twice (while your foot is still on the gas) thus making your revs shoot up and then as we all know...in most cases...the higher the revs the quicker your Z can be. Now this is felt big time when in first and second gear...but not as much in the higher gears. I must warn you...watch out it is very dangerous make sure that you are going in a straight line when you do it...because you can lose control if you have the wheel turned. Hope I helped...