Cranksets, Crank Arms, Bottom Brackets & Chainrings — UK Buyer's Guide

The crankset is the engine room of your drivetrain. It converts your leg power into forward motion via the chain, and choosing the right combination of crank, bottom bracket, and chainring makes a real difference to efficiency and reliability.

Cranksets — What's Included

A crankset typically consists of the two crank arms and the chainring(s) attached to the right arm. Cranksets are sold as complete units or with chainrings separate. Key specs are:

• Crank arm length — typically 165mm to 175mm. Shorter cranks suit smaller riders and improve hip clearance; longer cranks can increase leverage but may not suit everyone's anatomy. Most riders do well with 170mm or 172.5mm.
• Chainring configuration — 1x (single), 2x (double), or 3x (triple). 1x drivetrains are increasingly popular for their simplicity; 2x remains common on road bikes for a wider gear range.
• BCD (Bolt Circle Diameter) — the diameter of the circle formed by the chainring bolts. Must match if buying chainrings separately (e.g. 110mm BCD, 130mm BCD).

Bottom Brackets — The Hidden Component

The bottom bracket (BB) sits inside the frame's bottom bracket shell and houses the bearings that the crankset spindle rotates on. Getting the right BB is critical — the wrong standard will either not fit or cause creaking and premature wear.

Common standards include:

• BSA (threaded) — the traditional standard, still widely used. 68mm or 73mm shell width.
• PF30 / BB86 / BB92 (press-fit) — bearings press directly into the frame shell. Common on carbon frames.
• T47 — a newer threaded standard gaining popularity for its reliability.

Always check your frame's BB shell standard and your crankset's spindle diameter before buying.

Chainrings — Tooth Count and Compatibility

Chainring tooth count determines your gear ratios. A larger chainring = higher gear (faster on the flat, harder to push); smaller = lower gear (easier climbing). Match your chainring to your cassette range for a sensible overall gear spread.

Chainrings must be compatible with your chain speed (e.g. 11-speed chain requires an 11-speed chainring) and your crank's BCD.

Browse our cranksets, crank arms, bottom brackets and chainrings for a full range of drivetrain components.