Off road riding, especially the fun stuff, invariably involves navigating over tricky obstacles. If you bash into a log or rock, it will halt your progress as the front wheel compresses into the object (and attempts to catapult you off your bike or throw you sideways). Being able to unweight your front wheel is an essential skill for a good time in the hills. You'll be able to travel faster, and avoid nasties like snake bites (compression punctures) and buckled wheels.
There are two skills to learn:
1. The "Clean and Jerk"
Imagine yourself leaping into the air Michael Jordan style. You bend your legs then straighten them - exploding skywards. The same principle applies here only using your arms.
i) As you approach the obstacle, lift your butt off the seat and move your upper body forward and down over the handle bars. This compresses your body like a loaded spring, plus compresses the front tyre and your shocks.
ii) Quickly push away and back from the handle bars.
iii) When you run out of travel in your arms, bend them again to pull the bike towards your chest, lifting the front wheel off the ground.
When linked together in a continuous fluid motion you can snap the wheel in the air at a moments notice. Just the ticket for high speeds and unexpected water bars (gutters).
2. The Wheelie
Before getting excited about this one, best you re-visit Lesson One about braking. You need to keep a finger on the rear brake - because when you get this manoeuvre really dialled the only way you can avoid flipping right over backwards is by touching the rear brake. It's also advisable to practice without your clip-less pedals - allowing you to abandon ship in a hurry.
The idea is to get the bike to accelerate quickly underneath you - causing the front wheel to lift into the air.
i) Select a gear that will enable you to strongly accelerate the bike from a slow speed. This all will happen with a single power stroke, ie. the pedal moving between the 1 and 6 o'clock positions (see hill climbing). Too high a gear will result in too little acceleration and no wheel lift; too low a gear and the power stroke is all over in a jiffy causing only minimal lift.
ii) Once you've figured out which gear is right for you, practice applying a single explosive power stroke while cruising along the flat. Pulling against the handle bars will help apply more grunt to the pedals. If you can keep your arms straight then your weight will be more towards the rear of the bike which will help the lifting effect.
Timing is everything. You need to anticipate the obstacle - so start the move with your pedal in the 11 o'clock position. By the time your brain sends the action message to your leg the pedal will be ready for the power stroke at the 1 o'clock position.
This is best executed at slower speeds and is especially suited to gnarly hill climbs. Obviously the bigger the object, the more grunt you'll have to invest in the manoeuvre but in general it requires only minimal energy. And it sets you up nicely for unweighting the back wheel.