Velopedia Tools

Bike Geometry Calculator & Analyzer

Choose a bike and size. See what its geometry means.

Load a bike from the Archive or enter a geometry chart. Explore its proportions, steering and similar bikes.

Start with your bike

Find a bike → Choose size → Analyze

Choose a bike and size to load its published geometry.

Recommended · no geometry terms needed

Find your bike in the Archive

Search by year, brand or model, then choose a size.

Have a geometry chart?

Enter reach, stack and head angle below. Add wheel details for trail and BB height.

Enter the chart below
New to geometry? Explore an example

Interactive example

See where each measurement lives on the bike

Example only · not your bike

Loading the interactive geometry example…

Reach on this example398 mm

Horizontal bottom-bracket-to-head-tube coordinate.

This road/gravel example shows how the display works. Your analysis uses your chosen bike and size, then compares it with similar Archive bikes.

No particular bike in mind? Start with Bike Finder

Geometry input

Review or enter your measurements

Start with reach, stack and head angle from the same size and geometry position.

1

Frame geometry

Enter these three measurements from the same geometry chart.

? Horizontal distance from the bottom-bracket center to the top-center of the head tube.
? Vertical distance from the bottom-bracket center to the top-center of the head tube.
? The steering-axis angle measured up from level ground. A smaller number is slacker; a larger number is steeper.
More frame measurementsOptional · fork offset, wheelbase and more
? The perpendicular distance between the steering axis and front axle. It works with head angle and wheel radius to determine ground trail. Leave it blank when it is not published and Geometry Finder will still work.
Leave blank if unknown. Trail will be skipped.
? The published seat-tube angle measured from level ground. It is shown in the schematic when available but is not used to prescribe saddle position or fit.
Use the published angle; leave blank when it is not listed.
? Usually published as chainstay length: the direct distance from the bottom-bracket center to the rear axle center. Leave it blank when the manufacturer does not provide it.
Leave blank if unknown.
? How far the bottom-bracket center sits below the rear axle line. On a conventional equal-wheel bike, this is the published BB drop.
Leave blank if unknown. BB height will be skipped.
? Mixed-wheel bikes may publish a separate drop from the front axle line to the bottom bracket. Leave this blank when only one BB-drop value is published.
Mixed-wheel bikes only. Leave blank to use the rear/equal-wheel value.
? The direct distance from the bottom-bracket center to the front axle center. If it is not published, wheelbase can be used instead.
Direct BB-to-front-axle distance.
? The horizontal distance between the front and rear axle centers.
When front center is blank, the analyzer can infer it from wheelbase.
Wheel measurementsOptional · adds trail and BB height when frame data allows

Add wheel size and tire height, or enter a measured radius. Unknown wheels can stay blank.

Front wheel
? The rim diameter where the tire bead sits. Use the ISO/BSD number printed on the tire when available; 700C and 29-inch rims are normally 622 mm.
? The distance from the rim seat to the outside of the inflated tire. If you cannot measure it, the mounted tire width is a practical estimate.
Mounted width is a usable estimate when section height is unknown.
? Measure vertically from the center of the axle to the floor with the tire inflated. This is more accurate than estimating from rim and tire dimensions.
Axle center to ground; overrides the BSD estimate.
Rear wheel
? The rim diameter where the tire bead sits. On a mixed-wheel bike, select the rear standard separately from the front.
? The distance from the rim seat to the outside of the inflated rear tire. Mounted tire width is a practical estimate when height is unknown.
? Measure vertically from the rear axle center to the floor. Enter this when front and rear tire or wheel sizes differ.
Useful for different front/rear tires or mixed wheel sizes.
2

Archive comparison

Choose the category and size group for the comparison.

Modern comparison: Velopedia groups category, a recent model-year window and a normalized size band. Numeric and manufacturer-specific sizes are retained on the matching Archive records.

Geometry guide

Reading a geometry chart

No single number tells you how a bike will fit or handle. Start with frame proportions, steering and wheelbase, then consider them together. Bike category, wheel size and frame size all matter.

01

Frame proportion

Reach and stack describe the top of the head tube relative to the bottom bracket. Their relationship shows whether a frame is comparatively long and low, balanced, or tall for its length.

02

Steering

Head angle, wheel radius and fork offset combine to create ground trail. Head angle alone cannot fully describe steering response or self-centering.

03

Wheelbase

Wheelbase is the total axle-to-axle span. Front center and rear center show where that length sits relative to the bottom bracket.

04

Bottom-bracket height

Bottom-bracket drop describes the crank axis relative to the axle line; bottom-bracket height describes it relative to the ground. Tire radius connects the two.

Stack, reach and frame position

Reach is the horizontal distance from the bottom bracket to the top-center of the head tube; stack is the vertical distance. Stack-to-reach ratio is useful for comparing frame proportions without relying on inconsistent size names. It is not a fit prescription. Stem length, headset spacers, handlebar reach and rise, saddle position and rider proportions determine the actual contact points.

Head angle, fork offset and ground trail

Ground trail is the horizontal ground distance between the steering-axis intercept and the tire contact point. A slacker head angle, larger wheel radius or shorter fork offset generally increases trail; the reverse generally reduces it. Trail helps describe steering geometry, but tire deformation, load, handlebar width, front-center length and speed also influence the response a rider feels.

Trail = (R × cos θ − offset) ÷ sin θR is front-wheel radius and θ is the head angle measured from the ground. The result is geometric ground trail; it does not model mechanical trail normal to the steering axis, pneumatic trail or tire deformation.

Wheelbase, front center and rear center

Front center and rear center are direct bottom-bracket-to-axle dimensions. Bottom-bracket drop resolves those diagonal measurements horizontally. On a mixed-wheel bicycle the front and rear axle centers may sit at different heights, so the analyzer can use a separate published drop on each side. It can infer front center from wheelbase or calculate wheelbase from a supplied front center.

Rear horizontal = √(rear center² − rear BB drop²)Front horizontal = √(front center² − front BB drop²)  ·  Wheelbase = rear horizontal + front horizontal

Bottom-bracket drop and height

Bottom-bracket drop is a frame coordinate measured from an axle center. Bottom-bracket height is ground-relative, so wheel and tire radius matter. More drop can place the rider lower between equal-height wheels; less drop can preserve pedal clearance. When a mixed-wheel manufacturer publishes front/rear drop, keep both values: they describe the BB relative to two different axle heights. If drop is not published, leave it blank; the analyzer omits only the calculations that depend on it.

Archive method

Which bikes are used for comparison?

Similar category, size and years

The main comparison uses size-specific bikes in your selected category and a recent or selected year range. That range widens only when there are too few bikes to compare.

Repeated frames count once

Identical geometry is counted once so multiple builds of the same frame do not skew the comparison.

Broad comparisons, not precise rankings

Results use descriptions such as “near the middle” or “toward the longer end.” The available data does not support an exact percentile ranking.

Historical geometry as a secondary reference

Velopedia’s historical collection preserves head angle, wheelbase and rear-center measurements for thousands of bicycles from 1993–2007, but those source records do not identify frame size and do not contain modern reach or stack coordinates. The optional Historical reference view therefore compares only those three preserved chassis measurements. It does not treat a record as Medium, XL or a fit equivalent.

What “similar geometry” can—and cannot—tell you

Closest matches are numerical neighbors across shared measurements, with reach, stack, head angle and wheelbase carrying the most influence. They are useful for discovering bicycles with related static proportions. They do not prove equivalent fit, suspension behavior, ride feel, intended use or component setup, and nominal size labels remain manufacturer-specific.

Geometry terminology references: BikeCAD — front center, reach & stack · Trek — published geometry example
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