How to: Cranks

Two main factors for cranks are definitely strength and durability. There are three basic types of cranks,1-piece, 2-piece and 3-piece with different crank arm lenght ranging from 135mm up to 190mm according to rider's inseam length (see the sizing chart below).
 

	Inseam length	Crank Length
	20"	140mm
	21"	145mm
	22"	150mm
	23"	155mm
	24"	160mm
	25"	162mm
	26"	166mm
	27"	171mm
	28"	175mm
	29"	177mm
	30"	180mm
	31"	182mm
	32"	185mm

1-pc = designed for 1/2" pedals
2-pc = two piece cranks. Spindle is attached to one of the cranks arms
3-pc = three piece cranks. Spindle, Left crank arm, Right crank arm

See the picture above from the left: 2-pc cranks, 3-pc cranks with 19mm spindle and complete bottom bracket, 3-pc Primo cranks with 22mm spindle.

SPINDLES
There are various types of spindles in BMX. Dividing according to the shape: 4-edged, 6-edged, 8-edged, 48-spline. Dividing according to the size: 19mm, 22mm, 24m. The spindle diameter determines the size of bottom bracket bearings. More about bottom brackets in topic below.

From the left: 19mm 48-spline spindle, 22mm spindle for Primo cranks.
 

Recommended spindle size:
19mm spindle - For all riders under 70kg weight  
22mm spindle - For all riders over 70kg weight

GETTING YOUR NEW CRANK SET
Be aware of some crank sets that are suited mainly for one riding style (flatland, dirt/park, racing). Those will be quickly destroyed if you use them inappropriately. On the other hand, If you see any crank set with "suited for Street riding" in their name/description, you can be sure those are universal for everything and will last for years.

THINGS TO BE AWARE OF
In case of switching you rear hub from LHD(left hand drive) to RHD, it is important to check on your crank arms and see if there's a sprocket boss(hole for the sprocket bolt) on both of the arms (LHD/RHD compatible). It's not possible to put one of the crank arms on in the opposite direction.