How to know the bike size? All you need to know

Choosing the color, the group, the wheels or the components of your bicycle is very good but without a doubt the first decision, and one of the most important, is to choose the size of the bicycle.

What size bike do I need if I'm 1.70m or 1.80m? Do I need the same size bike for road as for MTB? Is a size M or L better for me? And according to my crotch, is a 54 or a 56 better for me?

It is very likely that some of these doubts are going through your head and that among your fears is that of making a serious mistake in the election. An error that can hardly be reversed and that you will have to drag along throughout the useful life of the bicycle. If you want to avoid making a serious mistake in your first purchase decision, it is important that you keep in mind the following indications. Some tips that should not only be followed by those who buy a new bicycle but also those who are looking for a second-hand bicycle.

First of all, comment that you can send me your questions through the comments and that all bicycle brands make available to their customers a technical sheet with the specific geometry of each model.

Choosing a bicycle size, a transcendental decision for the future.

The correct choice of size is essential both to maximize sports performance and to significantly reduce the risk of injury.

Although it may seem silly, a size error can cause physical problems that in the long run can cause pain even in your day to day life. Back problems, neck pain or knee discomfort can appear on many occasions due to a poor choice in the dimensions of the bike.

For this reason, it would be interesting if before making a final decision you let yourself be advised (in addition to these basic tips) by a specialist in the sector, such as a trusted biomechanist. A person specialized in this subject who can recommend you which bicycle is best suited to your conditions.

We take this opportunity to remember that it is always the bicycle that must adapt to us and not adapt our body to the bicycle with postures or forced positions that in the long term would end up generating important physical ailments.

It is also very important to be clear that although there are equivalence tables that will help you make a decision, the different brands and models have important differences that are as or more important than the size itself.

Some differences that are given by specific designs or geometries that adapt to certain profiles. There are much more racing bikes with a more aggressive aesthetic that are designed for competition, while other bikes are much taller in terms of steering and have a more cyclotourist geometry in which comfort prevails over aerodynamics. It is essential to be clear about what features we ask of a bicycle and what we generally look for in our day to day.

A sub 23 who is competing in amateur races will not need the same bicycle as a cyclist who seeks to lower his record in a cycling tour or a person over 50 who only goes out for fun on Sundays.

What bike sizes are there?

Originally the difference between brands was practically zero and a size 54 from one brand was practically traced to the same size from another manufacturer. The size, a 54 for example, referred to the length in centimeters of the vertical tube that connects the bottom bracket to the saddle. For this reason choosing the size was much easier.

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With the introduction of more aggressive geometries linked to aerodynamic studies and the appearance of slooping in bicycle designs, things have become much more complicated and currently a 54 does NOT have to measure 54 centimeters of horizontal tube. For this reason, the differences between brands (despite offering the same size) are more than notorious and it makes no sense to let ourselves be carried away by universal laws before making a decision.

Currently, bicycle brands offer sizes in 3 formats: Centimeters (size 54), inches (17.5'') or universal denominations (S, M, L...). Any of the three formats is good and although the conversions are never exact, we leave you with a table in which you can see the equivalences depending on the unit or format offered by the manufacturer. These changes appear especially between road bikes where the size is normally offered in centimeters and mountain bikes where inches and universal sizes are somewhat more widespread.

Equivalence table between size formats.

How to choose the size of your bike?

Generally, the choice of the size of the bicycle is usually associated with the height of the cyclist, but you should know that this should always be an orientation and never the definitive factor in your choice.

The explanation is very simple: Two people can measure 1.80 m but one will correspond to a size 54 and the other a 56. Why? Well, because they don't have the same long legs and their crotch doesn't measure the same.

Size table based on height: with the height of the person you can already have an orientation about what sizes are most suitable for both road bikes and MTBs.

Calculate crotch height – cycling

The crotch measurement is a somewhat more reliable factor than the height of the person and it will allow us to choose our bike size with more guarantees. In our article about saddle height we show you the best way to measure your inseam height.

Once you have measured the value of your crotch, that is, the distance between the ground and your crotch, (80 centimeters for example) you will be in a better position to make a decision. Generally, most brands offer selection advice both on their websites and in their specialized stores, and with this proven value in their product catalogs, it would be enough to avoid making any big mistakes.

If you want to know in a more general way what size of bicycle corresponds to you, you can multiply the value of the height of your crotch by 0.665. In this case 80 x 0.665 = 52.4 centimeters. So your ideal size probably won't be too far from a 52-54. We insist on the approach in this way and on the need to go to a biomechanist who, as a specialist in the field, can advise you better.

In this post you have a basic guide to correctly adjust the height of the saddle on your bicycle.

Size chart based on inseam height

If with the same approximation you want to know what size of mountain bike corresponds to you, we will multiply the result of the crotch, in centimeters, by 0.21, generating something like: 80 x 0.21 = 16.8. With which your ideal bike would be more or less close to 17 inches.

A matter of feeling

No matter how many indications or tips you may read, you should not forget that, after all, riding a bicycle is much more complex and the choice must be conditioned by our expectations. Expectations that vary greatly between people and that can range from the search for comfort to obtaining the most aerodynamic posture of all. A matter of feeling on the bike.

If you compete, you may be interested in choosing a slightly smaller bike size. Smaller frames are more manageable on the descents and it's always easier to get into an aero position. On the other hand, if you have any physical ailment, suffer from back pain or cycling tours and recreational events are your thing, I recommend that you opt for a larger bicycle size. As a general rule, larger frames are also more comfortable.