Help calibrate the model

This page works from a model of leg lengths, joint angles and frame geometry. Help me improve it: if you measure your bike and send me the numbers, I get a real reference point to check the calculation against.

Nothing is stored — no account, no database. The entries are assembled into a message, sent to me and then forgotten, exactly like a piece of feedback. You only need an email address if I should be able to ask about a number.

Take twenty minutes and a tape measure. Rough beats nothing: rather say where you were unsure than guess at a number.

Your bike

So that stack and reach can be looked up. If you know them, enter them straight away — then the rest is not needed.

For example Specialized, Canyon, Rose.

As printed on the frame, with the model year if you have it.

However the maker names it: 56, M, L.

From the geometry chart, if you have it handy.

From the same chart.

Your body

The two numbers everything in the model hangs on.

Barefoot, back against the wall, a book pulled firmly up into your crotch — then from the floor to the top of the book.

Measured on the bike

The real part. Bike upright against a wall, floor level, tyres at normal pressure. A straight board laid across the saddle or bar helps more than you would think — freehand you always measure crooked.

Bottom bracket centre to the top of the saddle, measured along the seat tube.

Vertically, at the highest point of the saddle.

Vertically, in the middle — where the stem clamps it.

Where the frame ends and the headset begins. This one number gives away the bottom bracket height and spares the model a guess.

Horizontally. A plumb line at the saddle tip, hanging free, touching nothing — then from the point on the floor to below the crank bolt.

Along the saddle, from the tip to the bolt with which the post grips the rails.

Cockpit and fittings

All read off, nothing measured — except the spacers.

Usually printed on the side, often as “±6°” or “17°”.

Ticked if it raises the bar rather than lowering it.

Headset cap and spacers together.

Stamped on the inside of the crank arm.

How far the clamp sits behind the post axis. A straight post means 0.

The length of the saddle goes into the calculation.

And how does it ride?

The most important thing last, and the only one that is not a number. A model can work out where your knee is — whether it hurts after three hours, only you know.

Does it fit? Does anything pinch, and from when? Have you ever changed something and noticed it got better?

Optional. Only so that I can ask if a number is unclear.