Carving the nose wheelie
Only use the front brake once into the turn.
It helps to practise first the plain fakie nose manual, so you already know how the balance point should feel as you switch from the nose wheelie going forward to the fakie nose manual.
Understanding the move
Keep the handlebars turned in the same original direction, with your hips close to the stem.
Hence you should be going at a comfortable speed, at least at a "jogging pace". Going too slow won't help as you won't be able to get the full centrifugal swing of the turn, and you wouldn't have much momentum left either after the initial nose wheelie (since you'll be using the front brake to lift up the rear wheel, hence the deceleration).Key to maintaining your balance going backwards is to always keep the handlebars turned in the same original direction relative to the frame, with your hips low and close to the stem.
Finish up the G-turn when you run out of momentum.
This will roll the front wheel inward your centre of gravity, bringing you back into balance (remember you're riding backwards now). Eventually, you'll reach a full stop when you run out of momentum (that'll be sooner if you are too heavy on the front brake).Learning the G-turn
1° Carve a tight turn with both tyres on the ground (preferably to your back foot side).
2° Lean forward into the turn, and feather the front brake so the rear wheel takes-off, keep your arms locked.
3° As the rear wheel leaves the ground, the centrifugal force swings the frame sideways, keep the direction tight.
4° Beyond 90° into the G-turn, the nose wheelie naturally switches to a fakie nose manual. Be softer on the front brake.
5° Keep the handlebars in the same original direction relative to the frame, turn more or less for lateral balance.
6° Try to carve the remaining 180° of the G-turn smoothly along a nice curve until you run out of momentum.
Bad habits
Typically, beginners have the bad habit to exaggerate the 180° endo with the hips (like you would for a regular
180° endo starting from a standstill), artificially swinging the frame around the steering tube and failing
to lock the handlebars into the turn.
Instead you should only rely on the spinning momentum you've built when carving the initial 90° of the turn
to keep spinning with the whole bike (not just the frame) as you reach the balance point over the front wheel.
Beyond 90° of the turn, focus on locking your arms with the bars always in the same direction relative to the
frame. Switching direction will eject you out of balance.
Keep the rear wheel fairly high as the whole bike swings around so you can switch to a fakie nose manual more
easily. Also, the higher you'll keep the rear wheel up, the easier it will be to spin over the front wheel without
being dragged sideways.
A well pumped up front tyre with less rolling friction will ease the spin and help the crucial switch to fakie nose manual.
Key is to keep the front wheel rolling of course, so you don't want to be too harsh on the front brake.
The more you rely on balance, the less you'll need to touch the brake, ideally you could even perform these G-turns brakeless like it is common practise in the BMX scene.
With plenty of practise, you'll be able to chain up one G-turn after next on sloping banks,
Ali C's style, relying on gravity to regain forward momentum after you've concluded your first G-turn to a full stop.
You can also check out Jimmy Ertzer's tutorial video to get a different view
(French subtitled in English).