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Free bike comparison tool
Enter two published geometry charts and see exactly how the candidate frame moves: higher or lower in stack, longer or shorter in reach. You get raw signed millimetres and a coordinate plot—not a fit score, body-based target or claim that one bike is better for you.
Frame coordinates
Your signed differences will appear here.
Enter the published stack and reach for both bikes. We will keep the raw millimetres visible and show which direction the candidate moves.
The coordinates
Stack is the vertical distance from the centre of the bottom bracket to the top-centre reference point of the head tube. More stack places that frame point higher. With the same fork, headset, spacers, stem and handlebar, it can support a more upright front-end starting point; less stack starts lower.
Reach is the horizontal distance between those same bottom-bracket and head-tube reference lines. More reach starts the front of the frame farther forward; less reach starts it closer. Because both measurements use the bottom bracket as their origin, they compare frames more consistently than top-tube length alone.
Before you compare
Important limit
Stack and reach stop at the frame's head-tube reference point. They do not include headset top caps or spacers, stem length and angle, handlebar reach or rise, hood position, saddle height and setback, crank length, shoe and cleat position, suspension sag, or the contact points your hands and pelvis actually use.
That is why identical frame coordinates can still produce different positions, and different frames can sometimes be configured to similar contact points. This comparator deliberately does not estimate torso or arm suitability, prescribe a size, calculate an “ideal” coordinate, or turn millimetres into a fit score. Use it to understand the frame delta and decide which physical measurements to compare next.
Buying another bike
Start with the raw frame delta, then ask for the complete cockpit specification. A 10 mm reach difference does not necessarily place the bars 10 mm farther from the saddle.
Comparing two sizes
Check both axes together, then compare standover, seat-tube limits, wheelbase and the stem each size would require. Do not choose from one coordinate alone.
Transferring a setup
Measure saddle and handlebar contact points from a repeatable datum. Frame stack and reach are context for that transfer, not substitutes for those measurements.
Use the full calculator for a cautious starting range based on your measurements, or review how OpenBikeFit labels evidence, conventions and limitations. If pain is sudden, severe, progressive or persistent, stop self-adjustment and seek an appropriate professional assessment.