Coasting and pumping can actually be faster than turning the cranks.
Gulleys, off-cambers and tight trees
Threading your mountain bike through tight gaps, like trees or gulleys, is not the place for pedalling — you can easily lose your footing on the pedal, or drive one of those platforms into an immovable object. At best you’re going to slow down, and at worst you might crash. Likewise, don’t pedal across short sections of off-camber, because pedal strikes are almost inevitable.
Pump it… Go light on the bike, pick the smoothest line possible and keep an eye out for any kind of downslope — look for rocks and ledges to pump. Push the rear wheel down on it to gain a little extra speed. Pumping off-cambers is tricky, but not impossible — try to get onto the backside of any root or rock.
Rocks, roots and bumps
The problem with pedalling is it puts your body in the wrong position to flow over obstacles, so instead of sucking up trail chatter with your arms and legs you end up crashing through everything. This robs you of speed, and precious energy.
Pump it… Press the bike down into the ground just before the first root or rock, like you’re preparing for a bunny hop, then go light as you cross the roots, allowing your weight to settle back down on smoother ground.
Switchbacks and linked corners
It’s tempting to put a crank in between two linked corners, but it can throw your weight off and ruin your line into and out of the second corner (the important one for maintaining speed). Just stay light after exiting the first corner and bring your weight back down onto the bike through the second, using that time to pick the best line.
Where to crank hard… Out of a corner. Tight corners usually kill your momentum. To improve your exit speed, start cranking as you begin to take off the lean angle. Just one well-timed pedal stroke can slingshot you out of the corner and down the next straight.