How it works

How I work out the bar position · How I decide whether a size fits · What to check

How I work out the bar position

Bar position is measured from the bottom bracket, horizontally (X) and vertically (Y), in millimetres. I take the centre of the bar where the stem clamps it and add the bar reach. That gives the front of the bend, where the shifters clamp on. Three things go into it:

1. Frame stack and reach, from the manufacturer’s geometry chart.
2. What sits on top of the head tube: the headset cover, the spacers and the stem (length and angle).
3. Bar reach, as published by the bar manufacturer.

Where a manufacturer doesn’t publish a dimension, I use a typical value (a −6° stem angle, say) and mark it with an asterisk. Shifters are left out, because you’ll set them up on the new bike as you had them on the old one. Different shifters or a different bar shape can move the hoods slightly, but rarely enough to need a different stem.

How I decide whether a size fits

For each size I ask three questions:

1. Can the bars reach your height with a sensible stack of spacers, leaving room to go up or down?
2. Does the stock stem do the job, or one slightly longer or shorter? For a size to fit, the stem can be up to 20 mm shorter than stock. It can be up to 30 mm longer, provided the manufacturer itself fits a stem that long on this model and it’s no longer than 120 mm (110 mm on gravel bikes). Would you rather keep the stock stem? Choose “Stock only” in the search.
3. Is the bar position within your tolerance? The default is ±10 mm.

If the answer is yes to all three, the size fits. Borderline means the size only works with no spacers or with the maximum, lands just outside your tolerance, or needs a stem 30 mm shorter. Anything else doesn’t fit, and I say why: the frame is too low, too tall, too short, too long or simply too big.

An integrated cockpit is treated like a stem, but only in the lengths the manufacturer makes for that model. If the result depends on swapping it, I say so.

A frame is too big when it needs a shorter stem than stock and almost no spacers: it’s both too long and too tall. A size like that is borderline at best, and the size below gets priority.

I show at most two adjacent sizes per model. If both fit, the choice is yours: it depends on where your saddle goes, how you want the bike to handle and how your position might change. If nothing fits, I show the closest size.

What to check

The saddle isn’t part of the calculation. The result assumes your saddle goes in the same place relative to the bottom bracket as it is now. Before you buy, check with the shop that the saddle can reach that height and setback, that the steerer is long enough for your spacers, and that the stem or bars can actually be swapped.

Real frames can be a few millimetres off the published geometry. Treat the result as a shortlist, not a measurement.

Your road position isn’t necessarily your gravel position. I use the numbers exactly as you enter them.

Older bikes: for archive models I only have the frame geometry. Second-hand bikes have often had parts swapped, so the stem is my suggestion. On an archive model’s page you can enter the stem and spacers actually on the bike.