Oh, and about the 20 feet thing, that will vary a lot by person and with different equipment. The force of friction at the rear contact patch will vary with the contact force (which will itself vary with how much the rider weighs and how much of his/her weight is over the rear wheel) and the coefficient of friction (which will vary with the two contact materials, and _I believe_, some combination of contact patch area and unit contact force)

So, basically, what works for one rider may not work for another, and so on. Find what works for you.