SERIAL: DEF-11 — TS: 26.04.26 — NODE: FR-DEFS
Bottom Bracket Height
Bottom bracket height is the vertical distance from the ground to the center of the bottom bracket.
Definition
Bottom bracket height is the vertical distance from the ground to the center of the bottom bracket. It is the absolute ride height of the cranks, dependent on wheel size and tire choice.
Analysis
Bottom bracket height describes the cranks' actual ground clearance. Unlike bottom bracket drop, it changes with wheel size, tire choice, tire pressure, and suspension sag.
Context
Bottom bracket height is reported in millimeters from the ground to the BB center with the bike held level on a specified tire size. Manufacturers usually state the tire used to compute the figure.
Function
Higher bottom brackets increase pedal-strike clearance and make the bike feel taller and more nimble at low speeds. Lower bottom brackets drop the rider's center of gravity for cornering stability and a more locked-in feel.
Variation
Bottom bracket height varies by discipline and tire choice. Trail riders sizing up their tires for grip will inadvertently raise BB height; cyclocross riders running narrow tires will lower it relative to the chart figure.
Common Ranges/Values
Road bikes typically have BB heights around 265 to 275 mm. Gravel bikes run 270 to 290 mm. Cross-country mountain bikes run 320 to 340 mm. Trail and enduro mountain bikes run 330 to 355 mm. Downhill bikes run as low as 340 to 350 mm at sag.
Common Practices & Evolution
BB height is rarely the primary number on geometry charts because it depends on tire choice. BB drop is preferred. Many full-suspension manufacturers report sagged BB height to give a more accurate riding figure.
Specifics
Sagged BB height (with rider weight compressing suspension) can be 15 to 30 mm lower than the static figure. Tire wear, pressure, and casing all measurably alter BB height.
Impact
Bottom bracket height is the figure riders feel directly when they pedal through a corner or over a rock. It is the practical ground clearance of the cranks.
Pros & Cons
Higher BB clears obstacles and works in technical terrain but raises center of gravity and reduces cornering security. Lower BB locks the bike into corners and feels confident at speed but increases pedal strikes and reduces ground clearance.
Relations
Bottom bracket height is the result of bottom bracket drop, wheel size, and tire size. It interacts with crank length, suspension sag, and rider weight.