Planting a foot when cornering: when and how? Recently I have noticed the following. When doing extremely tight turns e.g. 90 degree trail turn, I tend to:


Get out of my high saddle, position in front of it and low over the top tube
Stick the inside foot out, a couple of inches over the ground (easier on concrete, because it is smooth).


I have always thought of cornering as a trade-off between speed and safety. So doing the above, I feel safer, and am thus able to pass at a little more than walking speed.

One of two things can happen:


Because my center of gravity is now lower, the bike is tilted, and virtually all my weight is on the outside pedal, I make the turn.
Because I have entered the turn at too high speed, one or both tires begin slipping. I "fall" onto my foot, stepping firmly. As now all my weight is on the foot, I can "pick up" the bike and swing it around me in a crazy tight turn, then jump on it, while still moving.


My questions:


When is this appropriate technique and when would it be disaster?
What is the correct procedure for executing a planned foot plant?




Conclusion:

After I tried this on the trail a couple of times, my opinion is that planting foot is very different on smooth pavement and in rough terrain.

On smooth, but slippery pavement/ice, I can plant the foot momentarily, knowing that I will fall/slide out. The resulting acrobatic maneuver seems to increase the maximum possible speed in situations where no other technique would be appropriate. 

It's a pity that I don't have a picture of the place this thing is helping me. Basically, it is a part of my commute, and is a steep-ish ramp, with two 90 degree turns, which in winter is wet, snowy or icy. As I need to stay upright, this technique is pretty much all that can be done on those corners.

On the other hand, planting a foot while going down the trail is radically different. This is because on smooth surface, on can put their foot out, parallel to the ground, and very close to it, so as to anticipate slide-off. On an off-road terrain this is not possible and dabbing seems to be confined to "free get out of jail" functionality when you realize the "oh shit!".

Thanks Tyler Jandreau and Aaron!
While a "dab" isn't exactly the most graceful of techniques it's useful to save yourself from a spill or wipeout. What you need to ask yourself though is whether you leave a foot out because you're not sure what's going to happen when you turn or because you plan on going fast enough to slide around the turn. Sometimes the slide is unexpected and should just quick plant a foot and move on.

On the other hand, you're going to get a bunch of trail builders and riders who say that any slide is unwarranted and damages the trail. Generally this is true, but hardpack trails with dust on top or a little gravel are very easy to slide on and don't damage the trail at all. Mud, loam, and other loose soils are more prone to being disturbed by excessive sliding.

As for the proper technique for a dab, it's very dependent on your riding style. Here's a general breakdown of the timeline for a turn:


See the turn: Look ahead and see a tight/loose corner. Begin evaluating how you want to take it (eg. at speed, slow and upright, or sliding).
Begin the turn: Lean the bike towards the inside of the turn, pushing your weight to the outside pedal. Keep your inside foot relatively light.
Back tire breaks loose: Knowing when this will happen requires experience with your tires, so practice sliding in a parking lot or gravel road.
Plant foot: Remove your inside foot and place it slightly ahead of where you currently are, in the direction your moving.
Push through the turn: Push a bit with the inside foot, kind of a cross between a kick and step. This should keep your bike position or possibly move you a little more upright.
Re-engage and continue: Plant your foot back on the pedal and pedal out of the corner.


And that's more-or-less how it's done. Watch a bunch of Trail/AM/DH riders do it and you'll get a sense of where in the turn you should expect a plant.

Last bit, as you get more confident riding push more speed into the corner. You'll find that some spots where you previously needed to dab, you'll clear no problem due to the added force keeping your tires in place.