Cranks

Cranks are the vital bit of your bike which you pedal to move forward. They come in a variety of speeds, sizes and lengths, all of which can help tailor your bike to your riding style. Cranks connect to your bike via a bottom bracket (BB) that is often threaded or pressed into the frame. There’s a multitude of standards in how this all connects, so to find the right match you’ll need to know what’s what in that regard. A good place to start is with the bike frame itself, it will have a certain type and length of BB shell which will be the main deciding factor into what sort of BB you need and thus what type of cranks are compatible.

Beyond the compatibility, the main factors that distinguish cranks are the types of chainrings they’ll fit and the lengths and widths they’re available in. The BCD of the crank will determine what types of chainrings will fit with larger BCD cranks generally designed for bigger chainrings. Crank length ranges from about 140-190mm but most commonly around 165-180mm. The length you need is mostly related to your leg length. Longer legs generally like longer cranks. The other consideration surrounding crank length is ground clearance, with shorter cranks offering more protection from rock strikes etc while mountain biking. Crank width (called Q-Factor) determines how wide your stance will be on the bike. Road bikes tend to have narrow Q-Factors around 135mm whereas MTB cranks have wider Q-Factors to allow for the wider chainstays needed for MTB tyres.