[edit] Cranks

Cranks come in various guises, but all share the same purpose. They are connected to the bottom bracket and a chainring in order to propell the bike forwards. A full rotation of the cranks usually results in more then 1 rotation of the rear wheel (this ratio varies dependant on the amount of teeth on the front and rear chain ring, trials riders usually aim for around 1:1.20 ratio). Chainrings are affixed to the crank arm using 2 radically diffeing methods , both of which require differing drivetrain configurations . Traditionally , the chainring was affixed directly to the ( right side ) crank arm using a 4 or 5 arm " spider " and secured with bolts . Popular manufacturers of traditional cranks include Middleburn and Race Face .

Recently , Front Freewheel systems are increasingly popular , this system featuring a freewheel screwed onto threads around the B.B hole used in conjunction with a fixed hub at the rear . In trials use , cranks are often equipped with a bash ring , or frame mounted plate to avoid damage to the arms and chainring . Some crank arms require special pedal insert threads . Both systems offer various arm lengths including  175mm & 160 mm .