Methodology — RideGeometry

1. Your target handlebar position

Everything starts from where your hands should be relative to the bottom bracket: a horizontal distance (we call it HX) and a vertical one (HY), measured to the centre of the handlebar clamp. If you upload a fit report or enter your saddle and bar numbers we compute HX/HY directly: saddle height and setback place the saddle in space, then saddle-to-bar reach and drop place the bars.

If you only have body measurements, we estimate the position from published fitting rules: saddle height from inseam (the LeMond method, 0.883 × inseam), saddle setback from saddle height, reach from torso and arm length, and drop from your flexibility, age and how aggressive you want to be. Every number from this path is labelled estimated. It gets you into the right size; a fit report gets you the right setup.

2. Why stack and reach alone aren't enough

Same bar position, many frames: what the cockpit adds on top of stack and reach.

A frame's stack and reach describe the top of the head tube, not where your hands end up. Between the two sit the headset top cap, spacers, the stem (its length and angle) and the bar's own reach. Two frames 20 mm apart in reach can put the bars in exactly the same place with a 90 mm and a 110 mm stem. So for every frame we solve the cockpit: for each realistic stem angle we compute the exact stem length and spacer height that lands the bars on your target, then snap to parts you can actually buy (10 mm stems, 5 mm spacers).

Each discipline has a setup envelope of setups we consider sensible (road: 80–130 mm stems, up to 35 mm of spacers, −17° to +6°; gravel 60–110 mm; mountain bikes 35–70 mm) and a sweet spot in the middle (road: a 100 mm −6° stem with 15 mm of spacers, growing to 120 mm for the largest frames). Your ideal stack and reach are the frame that hits your target with the sweet-spot cockpit. The band around it is every frame that can still get there inside the envelope.

3. Handling

Your stable-to-nimble preference and the discipline set target windows for head tube angle, trail, chainstay length, wheelbase, bottom-bracket drop and front-centre. Wheelbase and front-centre scale with your frame size, so a size 61 isn't judged against a size 56 wheelbase. When a maker doesn't publish trail we compute it from head angle, fork offset and tyre size and mark it derived.

4. Scoring

Fit (0–100). Can this frame reach your bar position inside the envelope, and how close to the sweet spot? A frame that needs a 130 mm stem scores lower than one that works with 100 mm. Unreachable frames score zero, and we say what it would take.
Handling. How far head angle, trail, wheelbase, chainstay, BB drop and front-centre sit from your windows.
Use. Category match (an endurance bike still scores well for a road-racing request, with a penalty), tyre clearance against the width you want, wheel size, and fender or rack mounts if you asked for them.
Practical. Standover against your inseam, whether your saddle setback is reachable on that seat tube angle with a normal seatpost, and stock crank length.

The overall score is a weighted sum (road racing: fit 55 %, handling 20 %, use 15 %, practical 10 %). Weights, windows and envelopes live in a versioned configuration; every result records the version that produced it, so the same inputs always give the same answer.

5. What's estimated, and known limits

Body-measurement inputs are estimates and are labelled as such everywhere they appear.
Mountain-bike scoring uses static geometry; suspension sag is not modelled yet.
The saddle setback check assumes rails roughly 125 mm behind the nose; short-nose saddles differ by about 20 mm.
Derived trail assumes tyre height equals tyre width.
Geometry data is captured from makers' published charts and can lag mid-year changes. Every bike page shows its source and capture date.

6. Data provenance