What are cranks on a BMX?
The crank arm is where pedals are attached on a bike. BMX cranks set generally either come as a 3pcs which is 2 crank arms and a spindle, there are also 2pc BMX cranks which is 1 crank arm and a crank with spindle attached. 2.5pc BMX cranks are the same as 2pc but the spindle and arm can be separated on the 2nd pc. There is no particular advantage from one design to the next and although some may claim their design is stronger it may be true compared to their previous cranks or another design but may not run true compared to another brands BMX cranks.
What is the best size for a BMX crank?
BMX cranks and their respective spindle have 2 size options listed. There is the crank arm length which will between 160-175mm in 5mm increments. This is the length from the centre of the axle hole to the centre of the pedal hole. From a physics perspective the longer the crank arm the more leverage you have to pedal and so the easier it will feel to pedal in the same gear ratio compared to a shorter crank arm. However it may also be worth taking into consideration how you run your bike and the chain stay length as well. If you are running rear pegs on a street BMX frame then you will likely have short chain stays. This will likely work better with a 160-165mm crank to ensure you don’t catch you heel on a peg. Most park riders will generally opt for a 170mm crank arm length as this gives the leverage required to pick up speed quickly whilst also allowing for peg use. 175mm crank arms are generally used by trails and bowl riders who have a harder gear ration than average to enable them to go faster.
The other size for BMX cranks refers to the diameter of the crank axle. This will be either 19mm, 22mm or 24mm and you will need a bottom bracket to match this size to fit them to you bike. Crank spindles almost never snap, however the larger sized crank spindles allow for a larger end on the cranks arm which in turn generally will lead to a stronger crank arm. Most spindles are hollow to some degree and so the weights between the different sizes does not vary massively.