What Size Bike Do I Need?

As you can imagine, it’s very important to find the right bicycle size before you go out and make your first purchase. That might sound silly, but buying a fitted bike will most definitely enhance your biking experience, making it more comfortable and smoother overall.

Bike Sizing Guide

We’ve set up a bike sizing guide here so you can better understand the variety of factors in the formula, including bike type, structure, and the relevant measurements you need to calculate. So, here’s a compilation of the important information you’ll need to gather before shopping…

Bike Type

The very first step in this process is to think of and figure out what style of biking you’re going for: Are you riding on the roads for leisure, or do you prefer intense mountain biking?

Ribble R872 Carbon Road Bike with Di2 and Carbon Wheels

Or maybe you’re buying a bike for cross-country racing, or even just for exercise purposes. If you have a kid, figuring all that out is even more important, because things can get quite dangerous if their bike is too big for them.

So here’s some things to consider:

  • Where will you be riding the bike, meaning what kind of terrain will it be exposed to?
    Technical and steep downhill riding, challenging mountainous trails, dirt jump tracks, cyclocross mud racing, roads, or technical bridleways, all of these are just a few examples of what you’ll likely come up against terrain wise.
  • What are you using the bike for?
    Whether it’s commuting to work, sporting events, racing, touring, exercising, or off-road cycling, the purpose of the bike is directly linked to the bike type you’ll go for.
  • What bike position do you prefer – upright like mountain bikes, drop bar like road bikes, or BMX?
    Hybrid bikes and mountain bikes use flat bar handles so you can sit up tall and with your hands wide for good control. Adventure road bikes and BMX bikes use drop handlebars, designed for heavy duty use with off-road riding capabilities.

Woman Biking

Bike Measurements

You should understand how bikes are measured to know which of the many measurements are important to focus on. There are several factors to consider here, including the frame size, seat position, and seat tube length. Naturally, the type of bike you buy will also factor in to the bike size.

Frame Size

The size of the frame is super important as to avoid putting in extra effort when you bike. If the frame is too small, you’ll feel cramped and won’t be able to extend your legs for maximum power as you pedal. Alternatively, if the frame is too big, you won’t reach maximum power either because you won’t be able to extend your legs enough.

So, how do you know the frame size that works for you? ?


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    Easy: stand over the frame with both legs on either side. If it’s a racing, hybrid, or touring bike,  there should be an inch or so of space between your crotch and the frame. For mountain bikes, this space should be greater.

    Bike Frame

    For children, ensure that the balls of their feet touch the ground and grab the handlebars easily while they’re sitting on the seat. If they’re standing over the center bar, there should be a 20-25mm space between their crotch and the frame.

    Wheel Size

    Wheel sizes are usually distinguished by their primary use – road biking, mountain biking, off-road, BMX, or touring. Mountain bikes, leisure bikes, and road bikes are usually between 26” and 29” in diameter and 2.2” in width.

    BMX wheels tend to be smaller than this as they’re used in stunts and jumps, so they can withstand additional loads. On the other hand, children’s bikes are between 12” and 16” in diameter based on the child’s age (between 3 and 7 years).

    Seat-Tube Length

    Bikes are also measured by their seat-tube length. This is measured from the center of the bottom bracket or the bolt that attaches the crank arms, noting here that this can differ from one brand to another. Some measure to the point where the top tube meets the seat tube, and others measure to the center of the top tube.

    bike size explained

    Mountain bikes are measured in inches, or by the descriptors (small, medium, and large). Road bikes are measured in centimeters and descriptors, and hybrid bikes can be measured by either.

    Seat Position

    The perfect seat position for you ultimately depends on your preference, whether its tilted forward, backward, or level. However, best practice indicates that the seat should be positioned so that there’s no discomfort when you extend your legs and rest your feet on the pedals. Make sure you’re not moving your hips from side to side to pedal comfortably.

    Handlebars, Pedals, and Cranks

    The handlebar position is more important than you think. An uncomfortable one can lead to shoulder, wrist, and back pain. Their size depends on the bike size, and their width and height depend on the bike type. The more upright you prefer your position on the bike, the higher they need to be. With us so far? Great!

    Pedals are connected to cranks, which provide the bike with power. Clipless pedals allow for maximum efficiency, wherein every motion you make will provide the bike with some power.

    Muddy Mountain Bike Clipless Pedal

    These come in different varieties depending on the bike type. Toe clips, on the other hand, fasten your feet in and are more heavy, but they allow you to use normal shoes rather than cycling shoes. Mountain bikes use dual-sided pedals to be able to withstand rough terrain.

    Your Measurements

    To work out all the above, you also need to know your measurements. Here are the important ones you need to know:

    • Height: Stand against a wall and measure from the ground up.
    • Leg in-seam: This measurement is from your crotch (where the seat would be) to your foot.
    • Arm length: From the end of your collarbone, all the way to the middle of your fist.
    • Torso length: From the curve below your neck to your crotch.

    Once you get these measurements, refer to the chart below to get a good idea of the bike size you need.

    determining your bike size

    Additionally, you can find an online bike fit calculator for some extra help in knowing what exact bike size you need. This wraps up our bike size guide for finding your perfect bicycle fit. You’re now good to go!

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    What Size Bike Do I Need? — Bike Hacks