Why You Shouldn’t Rely on Standard Bike Sizes (S, M, L, 54cm, etc.)
It might seem like a safe bet to walk into a shop, say your height, and roll out with a size Medium or a 54cm frame. After all, that’s how most people get sized — and most bike shops still rely on it. But here’s the truth: those standard size labels? They mean almost nothing.
A Medium in one brand can fit completely differently from a Medium in another. Even worse, a “54cm” from one manufacturer might ride more like a 56cm or a 52cm elsewhere. And if you’re about to drop $10K or more on a new bike, using guesswork or generic sizing advice is a fast track to discomfort, poor handling, and wasted money. In this post, we’ll break down why standard sizing and height charts are outdated tools — and show you what actually matters when choosing your next bike: real geometry, stack and reach, and fit tailored to you.
Standard Sizes Are Not Standard at All!
Bike sizes aren’t universal. One brand’s Medium might be another brand’s Small. A 54cm frame from one manufacturer could fit more like a 56cm from another. These labels are just rough indicators and don’t reflect actual frame geometry — which is what determines how the bike fits you.
Even among top-tier bikes, stack and reach can vary significantly between two frames labeled the same size. And when you’re potentially spending upwards of $10K–$20K on a high-end bike, guessing the size based on a vague label is a massive gamble.
Height Charts Are a Shortcut to Getting It Wrong
Walk into a bike shop and they’ll often size you based on your height — “Oh, you’re 175cm? You’ll be a Medium.” But height alone doesn’t account for torso length, leg length, flexibility, posture, or riding style. Two riders the same height can have completely different fit needs.
Sizing based on height is more of a convenience tool for sales than a reliable method for fit. It might get you “close,” but close isn’t good enough when it comes to preventing discomfort, injury, or wasted money.
The Smarter Way to Size a Bike
Stack and reach are the only reliable numbers to compare bike fits between brands and models. They define the vertical and horizontal positioning of the bike’s front end — which directly affects posture, comfort, and weight distribution on the bike.
If you want to know whether a bike actually fits, compare its stack and reach to your ideal position — not just a size tag. That’s exactly what we do in every pre-purchase fit. Better still, while you might’ve come across sites like Geometry Geeks, we know the frustrations — outdated data, broken links, and missing models. That’s why we’re building our own bike geometry database, launching mid-2025. It’ll be completely free to access and designed to give riders like you clean, accurate data you can trust with bike data from all brands.
Ready to Take the Guesswork Out of Your Next Bike?
Choosing the right bike isn’t about picking a size label — it’s about matching the bike’s geometry to your body. Whether you’re eyeing up a high-end road machine, a gravel bike, or a versatile commuter, getting the fit right from the start can save you thousands and completely transform your riding experience.
Let us do the hard work for you. Book a Pre-Purchase Fit and we’ll provide a personalised list of bikes that fit you perfectly, backed by real data — not guesswork.
