rhyang wrote:.. you jam more vertically instead of sticking your foot straight in .. hard to explain online...
I'm not a 12 crack climber but that's the basic or foundation of a correct start of foot jam. The same as a ham jam. Majority of the time you want to go with big toe up, small toe down, with the bottom of your shoes paralleling the crack. How deep you stick your foot in depending on the size of the crack and foot. After that you want to twist your foot and lock. A correct foot or hand jam should NOT hurt. Crack climbing technique came to me easy. A lot of my friends cannot climb crack and think it is not natural climbing technique. There's a constant fear of their hand or foot getting stuck should they fall.
Not the best picture but it goes something like this: