hi guys im new and i am confused about bmx cassette wheels what they are how they are different to free wheels. i think it means that the crank (peddals) are spinning with the wheels and they dont stop unless the wheels stop spinning ,or dose it mean when you go down a hill the crank grips on straight away instead of trying to catch up to the wheels speed? I DONT KNOW PLEASE HELP ME!!!!!! and use as much detail as posible thanx luke.