Need empirical evidence to prove that you should roll fast through rock gardens? Lee McCormack, co-author of Mastering Mountain Bike Skills, has a nice illustrated overview of the scientific principles involved on his blog Lee Likes Bikes. Basically:
The faster you go, the less the wheel drops. Twice as fast equals one-quarter the drop. At 8 mph you drop a stop-dead 12.6 inches; at 16 mph you drop a pond-skimming 3.2 inches.
As a result, your wheel approaches the next rock at a better angle of attack. Of course this is exaggerated more greatly with a 29er which allows you to reduce your speed somewhat and still make it through.
