Cycling

Bicycle bottom bracket (BB) shells connect the frame to the rotating crankset spindle. Traditional standards include BSA English Threaded (68/73 mm shell width, 1.37" × 24 TPI, reverse left-hand thread on drive side) and Italian Threaded (70 mm shell, 36 mm × 24 TPI right-hand both sides). Modern press-fit and oversized standards include BB30 (68/73 mm × 42 mm press-fit), PF30 (68/73 mm × 46 mm), BB86/92 (86.5/91.5 mm × 41 mm), and T47 (threaded M47 × 1.0 mm).

Bicycle roller chains are standardized under ANSI B29.1 and ISO 9633. Across all modern bicycles, the chain pitch (distance between consecutive pin centers) is strictly 1/2 in (12.7 mm). Drivetrain speeds (1-speed to 13-speed) differ in internal roller width (1/8" for single-speed down to 11/128" for 11/12/13-speed) and external pin length (tapering from 8.6 mm on 1-speed to 5.25 mm on 12-speed chains).

Bicycle handlebar and stem clamp diameters are standardized across road, gravel, mountain, and BMX disciplines. The dominant modern standard for road, gravel, and trail bicycles is 31.8 mm (1¼ in). Modern downhill, enduro, and aggressive trail mountain bikes frequently use oversized 35.0 mm clamps for increased torsional stiffness. Legacy standards include 25.4 mm (1.0 in; ISO standard for older road/MTB), 26.0 mm (Italian road), and 22.2 mm (7/8 in; BMX and MTB grip ends).

Bicycle inner tubes and tubeless systems utilize three primary valve standards: Presta (Sclaverand / French valve; 6 mm stem diameter, manual locknut tip, rated up to 15 bar / 220 psi), Schrader (American / Auto valve; 8 mm stem diameter, spring-loaded central pin, ISO 4570 thread, 0.305"-32 TPI), and Dunlop (Woods / English valve; 8 mm stem diameter, drop-in core).

Bicycle tire and rim dimensions are standardized internationally under ISO 5775 and the ETRTO (European Tyre and Rim Technical Organisation) system. Sizing is defined by two numbers: nominal tire width and Bead Seat Diameter (BSD) in millimeters (e.g. 28-622). Major standards include 700c / 29er (BSD 622 mm), 27.5" / 650b (BSD 584 mm), 26" MTB (BSD 559 mm), 650c (BSD 571 mm), and 20" BMX (BSD 406 mm).