The letter size (S/M/L) and the old seat tube measurement stopped telling you whether a bike fits — each brand assigns them its own way. Today fit is decided by reach: it measures the real length of your standing position and is comparable across brands. If a bike that fits you has a certain reach, look for a similar one on any other, ignoring the letter. Reach is the common language; the size is just a label.
It's the most important shift in mindset for buying well today: stop thinking "I'm an M" and start thinking "my reach is X".
You used to ask "what size am I?". Today the right question is "what reach fits me?". Anyone still choosing by the letter is buying blind.
The old system measured the frame by its seat tube length (the "18 inches" of yesteryear). It made sense when the saddle sat at a fixed height and the tube defined the size. But then came dropper posts, which adjust saddle height on the fly, and suddenly seat tube length stopped defining anything about your position. Today brands make short seat tubes in every size so the dropper fits — so that number no longer tells you how long the cockpit is. The S/M/L letter inherited the problem: it guides, but it doesn't measure.
The reach is the horizontal distance from the bottom bracket to the head tube: the length of your standing cockpit, which is what really determines whether a bike feels long, short or just right when you're standing on the pedals — the position that matters most in MTB. And because it's a number in millimeters with the same definition across every brand, it compares directly. Two bikes with the same reach will give you a similar cockpit even if one is an "M" and the other an "L".
It works as a quick orientation: it tells you which zone of the catalog to look in before getting into detail. But the moment you compare two specific bikes —and especially from different brands— the letter can fool you, and reach won't. Think of size as the sign above the aisle in a shop and reach as your shoe size: the sign leads you to the shelf, but you try things on by the number.
Reach. The S/M/L letter guides, but each brand assigns it differently; reach measures real fit and compares across brands.
With dropper posts, the seat tube no longer defines your position. Reach took over that role.
Ignore the letter and compare reach (and stack). Look for a reach close to that of a bike that fits you well.
Tell us your current bike or your measurements and we'll tell you your target reach to choose with any brand. Message us on WhatsApp
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