Let's say we are looking to upshift. The rpms go up to the point of shifting, the clutch is depressed, and the transmission is taken out of gear. Immediately, the clutch is again depressed (hence, the double clutch), and the transmission is shifted into the next gear. This is done for trannys without sychros (trucks). For upshifting, double-clutching is nothing more than a " timing thing" to allow for the engine rpms to match the road speed of the wheels which allows the appropriate shift.

It sounds complicated, but it is actually a simple concept when you realize what is going on.

David Liske