54 or 56? What to Do When You Are Between Road Bike Sizes

By Mike · Updated 13 July 2026

Almost nobody sits perfectly in the middle of a size range. The between-sizes dilemma, 52 or 54, 54 or 56, M or L, is the single most common sizing question we get in the shop, and the honest answer is that it cannot be answered from height alone. Here is how we actually work it out.

Why between happens

Size charts are built around an average body. If your legs are long for your height, you push toward the smaller frame with the saddle raised. If your torso and arms are long, you push toward the larger frame or a longer stem. Flexibility moves the answer too: a rider who can comfortably hold a lower, longer position tolerates the bigger frame better than a rider who cannot.

So when two sizes both look plausible on paper, the deciding information is not on the chart. It is in your proportions and how you ride.

The general tendency, and when to ignore it

If forced to a rule of thumb: when genuinely torn, the smaller frame is the more recoverable mistake. Seatposts extend, stems lengthen, spacers rise. A frame that is too large offers far fewer escape routes, and a very short stem on a big frame makes the steering nervous.

But rules of thumb are where sizing mistakes come from. Ignore the tendency when your torso is long relative to your legs, when you value stability over agility, or when the specific model runs small or large, which brands genuinely do.

The same rider, three brands, different answers

Take the brands on our own floor. Giant sizes its road bikes S, M and L rather than in centimetres, and its compact frames mean the same rider often takes what feels like a smaller label than expected. Merida and Orbea size in centimetres or letters depending on the model, and their race and endurance platforms differ meaningfully in stack and reach at the same nominal size. The result: it is completely normal to be one size in one brand and the neighbouring size in another, and nothing is wrong with you or the bikes when that happens.

This is why the honest comparison is stack and reach rather than the size label, as covered in our road bike sizing guide. Hold the two candidate sizes' numbers side by side and the choice usually becomes obvious: one of them will sit clearly closer to the position your body actually needs.

How to settle it for good

The reliable path: get your body measured once, properly. A sizing assessment gives you target coordinates, and every between-sizes decision after that becomes arithmetic. We run these at our Cheltenham studio, on their own or as part of a full functional fit, and the numbers go into a written report you keep. If you are weighing up a specific bike right now, ours or anyone's, bring the geometry chart and we will tell you which size the numbers support.

And if the bike in question is second-hand, where there is no exchanging the frame later, read our used road bike buyer's guide before you commit. Size is the first checkpoint on that list for a reason. Both sizes on your shortlist might be available in our pre-owned range anyway, in which case the answer is simple: come in and ride them back to back.