Cranksets

BMX race cranksets: crank arms and spindle as one assembly

A crankset is the complete assembly: both crank arms, the spindle that joins them through the frame, the pinch or spindle bolts and usually the setup spacers. If you only need to replace a single bent arm after a crash, what you are looking for is a BMX crank arm sold separately. This is the part that takes the most violent torque in the sport: the effort put in on the gate.

Three-piece, two-piece, one-piece: three architectures

The three-piece crankset is the racing standard: two independent arms and a separate spindle, usually splined, clamped by a bolt at each end. It lets you replace a single arm and change the spindle to suit the bottom bracket. A two-piece crankset has the spindle pressed into the drive-side arm, which means faster fitting and one interface less, but no mixing and matching. The one-piece crank, a single bent steel forging running through an American bottom bracket, is now only found on beginner bikes.

Crank arm lengths and rider classes

• Micro and Mini: 127 to 150 mm, to keep a high cadence on short legs.
• Junior and Expert: 145 to 165 mm, the widest range in the catalogue.
• Expert XL and Pro: 165 to 180 mm depending on rider height and gate style.
• Cruiser: often 175 to 180 mm, since a 24 inch bike has more generous ground clearance.

A longer crank arm gains torque but loses turning speed and brings the pedal closer to the ground in banked turns. If you are torn between two sizes, the shorter length is almost always the right call for a growing rider.

Spindle diameter and bottom bracket standard

Spindle diameter determines the bottom bracket. 19 mm spindles fit most three-piece cranksets, 22 mm the stiffest models, and 24 mm spindles carried over from mountain biking still turn up. On the frame side, the common standards are Euro BB (threaded, 68 or 73 mm), Mid BB, Spanish BB and American BB. Check shell width and inside diameter before ordering your bottom bracket: the same crankset will fit several standards provided you use the right cups and spacers.

Chainring interface and chain line

Chainrings mount most often on a 4-bolt, 104 mm BCD pattern, and sometimes directly on the spindle splines depending on the brand. Once the crankset is in, check the chain line: the BMX chainring and the rear sprocket must sit in the same plane, otherwise the chain jumps off on the gate and wears at an angle. The spacers supplied with the spindle exist precisely for this adjustment.

Materials and stiffness

Forged 7075 aluminium dominates the market: a good balance of stiffness, weight and price, with reasonable tolerance to pedal strikes. Carbon crank arms drop noticeably more weight and damp vibration better, but cope poorly with side impacts against a gate or a rail. Chromoly steel now survives only on beginner sets.

The BMX race crankset brands

Inspyre builds high-end sets focused on stiffness. Chase covers the full length range, from Micro to Pro. Box Components offers cranksets widely seen on complete bikes. Supercross and Crupi round out the range with careful machining and finishes that match their frames.

The BMX RACING advice

Tell us the rider's height, your frame's bottom bracket standard and your current gearing, and we will confirm length, spindle diameter and cup set before we ship. Always tighten crank bolts with a torque wrench to the manufacturer's figure, and re-check them after the first session. Dispatched within 24 to 72 hours and you can spread the cost over 2 or 3 payments with Alma.