logoRolling Over the obstacle
A pure biketrials technique that will take you up any gnarly rocks and odd shapes, without a lot of run up distance and virtually no effort. But it takes a good synchronisation of the pedaling and the weight transfer on the front wheel to make it roll smoothly.

Start about one crank turn away from the obstacle...on your good pedal. Roll the first half crank turn slowly to approach the step or wall, gaining a bit of momentum.
1° On the second half crank turn, push on the goofy pedal (left) to lift the front wheel up to the edge of the obstacle. You must aim right at the edge, not behind. 2° As the front wheel takes off, keep the knees slightly flexed, ready for an impulsion as soon as the front wheel passes or touches the top of the kerb. 3° Finish the crank turn on your good pedal and, from the highest position (on the pedals), throw your shoulders over the bars with an impulsion upwards.
The rear wheel takes off while the front wheel rolls on the obstacle.
See the move in a video

Smooth...Smooth
This is technically the smoothest way to climb. You should really force yourself to lift the front wheel only when pushing on the wrong pedal, so that you can be ready on the good pedal to take your impulsion when the front wheel touches, and throw your shoulders over the bars to lift the rear wheel. When the move is well done, you can even roll directly on the front wheel, passing over the edge of the obstacle without touching it. At the beginning, you'll tend to smash your crank into the edge you're trying to climb, so get yourself a decent rock ring. A bad habit is to use the front brake once the front wheel has landed, to give some extra lift to the rear wheel. But you should really try to learn without braking on the front (else, how do you get the rolling part?).
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Rolling over...so...so

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Rolling over a concrete pipe
The next level
When the obstacle is too high for just touching the edge of the wall with the front wheel, then the rollover technique can be pushed to its limit by giving a strong impulsion in the good pedal just before take off, and throwing your shoulder and body weight over the bars even before the front wheel reaches the obstacle.
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Mastering the technique
You end up in the air, with the front wheel above the edge of the obstacle, and using your body inertia to pull the bike upwards with you, over the edge. This could look like a bunny hop, but there is a huge difference: your body weight is really in front of the bike over the bars, and you land on the front wheel instead of landing on the rear. If you overdo it, you just end up rolling in balance on the front wheel. In some rare cases, you'll be able to use a little lump in the run up space to pull a bunny hop and carry on as a rollover (because landing on the rear would make you fall back. The next technique, starting exactly the same, is to bang the front wheel on the edge of the wall or just below, in an ascending move. video
A mix of bunny hop and rollover
You'll need a lot of practice before you can even think about it. In the mean time, you can try to climb onto small kerbs sideways. Quite safe, and virtually no space needed.

At a Pro level: pushing the move further
Rolling over is an amazingly smooth technique when fully exploited by top riders, with loads of variations and finish styles. It really looks as if there is direct a slope. Depending on the obstacle, the real trick is to throw the body far enough to ensure plenty of momentum and a good grip.
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Thomas Oehler finishes on the front.
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Front to back-wheel swap (Waynio)
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Smooth touch from Ben Savage