Bottom Brackets vs. Wheel Sizes
Comparing 2 standards across 20 specifications. 20 key differences identified.
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 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).
Specification Comparison Table
20 Parameters| Parameter / Spec | ||
|---|---|---|
|
BSA English Threaded Shell Width
|
68.0 (Road) / 73.0 (MTB) mm shell width | — |
|
BSA Thread Specification
|
1.37 in × 24 TPI (ISO 6698) Left-hand drive side / Right-hand non-drive | — |
|
Italian Threaded Shell
|
70.0 mm width / 36 mm × 24 TPI Right-hand thread on both sides | — |
|
T47 Threaded Standard
|
68.0 / 73.0 / 86.5 mm width M47 × 1.0 mm internal thread (fits 30 mm & DUB) | — |
|
BB30 Press-Fit Standard
|
68.0 (Road) / 73.0 (MTB) × 42.0 mm (42 mm bore, bearings pressed directly into shell) | — |
|
PF30 Press-Fit Standard
|
68.0 (Road) / 73.0 (MTB) × 46.0 mm (46 mm bore with composite bearing cups) | — |
|
BB86 (Road) / BB92 (MTB) Press-Fit
|
86.5 (Road) / 91.5 (MTB) × 41.0 mm (41 mm bore, designed for 24 mm spindles) | — |
|
Shimano Hollowtech II Spindle Diameter
|
24.0 mm chromoly steel spindle | — |
|
SRAM DUB Spindle Diameter
|
28.99 mm aluminum alloy universal spindle | — |
|
BB30 / 30mm Spindle Diameter
|
30.0 mm oversized alloy spindle | — |
|
700c Road / 29" MTB BSD
|
— | 622.0 mm Bead Seat Diameter (ISO xx-622) |
|
27.5" MTB / 650b Gravel BSD
|
— | 584.0 mm Bead Seat Diameter (ISO xx-584) |
|
26" Mountain Bike BSD
|
— | 559.0 mm Bead Seat Diameter (ISO xx-559 classic MTB) |
|
650c Triathlon / Road BSD
|
— | 571.0 mm Bead Seat Diameter (ISO xx-571) |
|
20" BMX (Standard) BSD
|
— | 406.0 mm Bead Seat Diameter (ISO xx-406) |
|
20" BMX (Race / Junior) BSD
|
— | 451.0 mm Bead Seat Diameter (ISO xx-451) |
|
16" Folding Bike (Brompton) BSD
|
— | 349.0 mm Bead Seat Diameter (ISO xx-349) |
|
Road Tire Width Range
|
— | 23.0–32.0 mm (e.g. 25-622, 28-622, 32-622) |
|
Gravel Tire Width Range
|
— | 35.0–50.0 mm (e.g. 40-622, 47-584) |
|
MTB Tire Width Range
|
— | 53.0–66.0 mm (2.1–2.6 in / e.g. 60-622, 65-584) |