hey shants,
that's a great explanation.

however, i want to address the "if you skid in 2 opposite positions it will double the number of skidspots."

gear ratio 3.0 (e.g. 48x16)
if you skid in 2 opposite positions, it will yield double the # of skidspots. a half revolution of the cranks will turn the rear wheel 1.5 times, which results in a new skidspot.

gear ratio 2.0 (e.g. 40x20)
if you skid in 2 opposite positions, it still yields only 1 skidspot. a half revolution of the cranks will turn the wheel once, which means you'd be skidding on the same spot.

after carefully thinking about this, i think it ends up like this: if your gear ratio is an even whole number, using 2 opposite crank positions for skidding will not double the number of skid spots.

however, this makes me wonder if this has any ramifications for other less even gear ratios. but can't quite get into thinking about that now.