Downhill longboarding is purely racing down steep hills at insane speeds. Downhill boards are typically in the mid 40" range. These boards are stiff and low to the ground. Having a lower center of gravity increases the speed of the board.

Downhill longboarding is extremely dangerous. In competitions, downhill skaters will wear a full face helmet and protective clothing. Skaters can hit speeds over 40 MPH, which is faster than I usually drive.
This guy is the man

Cruising and Carving