I want to buy a new mountain bike but I'm not really sure what size to get. I'm 1m72 and I see XL and L frames everywhere, but I'm worried I'll mess up and end up with something uncomfortable. Is there a formula or something to calculate it correctly?
I've seen a lot of people make the mistake of just grabbing a generic size chart without digging deeper. What really matters is how the frame positions you once you're on it - the size in cm or letters is just a starting point. At 1m72, you'll definitely swing between M and L depending on the brand, but here's the thing people often forget: your arm-to-leg proportions matter too. If you've got legs that are a bit longer than average for your height, an L might be more suitable, even if the standard charts suggest an M.
The best approach is really to actually get in the saddle and feel it out. Look at how things are at the handlebars - you need to be able to keep your back slightly tilted without being bent double, and your arms a bit bent, not straight or too cramped. On a mountain bike it's a bit different from a road bike, the positioning is more upright. If you can, try one out at a legit retailer who has stuff you can test ride - you'll see right away what works for you. And even after you buy, adjustable stems and seat tubes can fix quite a bit of stuff if you're right on the edge between two sizes.
At 1m72 you're right in the M/L zone according to most brands, so before you decide check the specific size charts from the manufacturer because it varies from brand to brand. The most reliable thing is to base it on your inseam (the distance from the ground to your crotch when you're standing straight) - most bikes give a range for this measurement, it's more accurate than just height. After that if you can, try the bike in store or ask for a decent return policy, because the wrong size gets uncomfortable fast and it really changes how you ride.
Have you thought about measuring your inseam instead of just going by your overall height? It's honestly way more reliable for mountain biking because it really comes down to the frame geometry and how long your legs are. Most brands give you a formula like inseam in centimeters divided by 2.65 to get the size in inches, but honestly the best thing is to go to a shop and actually sit on one - your riding position, the reach to the handlebars, all that matters way more than just numbers on paper.
The thing that really works is going to a shop to test it in riding position rather than just looking at the numbers - you'll immediately feel if you're comfortable or cramped. If you can't do that, ask the shop to also check the top tube length (not just the frame height) because it varies a lot between brands, and once it's too long or too short it's a pain to compensate for after the fact.
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