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How to choose your bike size

How to choose your bike size

Here's a question that comes up often! the acquisition of a new bike isn't an investment to be taken lightly: hence why you should never hesitate on this point. A bike that matches your body will bring you comfort, performance and maneuverability, whereas an ill-adapted bike will quickly cause discomfort and pain that will transform your favorite activity into a unforeseen ordeal!

There are now many brands on the market and each tends to take measures in its own way, so we'll try to orient you in order to find the bike size that suits you best.

What do bike sizes corrrespond with?

Historically, all bicycle frames had a right upper tube and the length of the seat tube defined the size of the bike, but this notion has become outdated with the appearance of new geometries: sloping road bike frames (inclined top tube) , full-suspended MTBs, city bikes, etc...

Indeed, some manufacturers now use international sizes (S, M, L ...), some continue to indicate their sizes in "real sizes" (which is therefore a virtual measure on a sloping frame), while others have begun to indicate sloping sizes. So you have to be careful about how the manufacturer indicates measurements and make sure you find the right bike for you.

What steps should be taken?

Choice of wheel size

The necessary steps to choose your new bike are size, crotch height and arm amplitude.

Start by measuring your crotch height. For this, stand upright against a wall, bare feet slightly spread (about 20 cm) and heels well in contact with the wall. Place a rigid support (a book will do), in contact with your perineum (muscle that is in contact with the saddle when you are on the bike). Then, with the help of another person, take the measurement from the ground to the top of the book, then multiply the value obtained by 0.665 to obtain a road bike's real size in centimetres or by 0.226 to get an actual MTB size in inches.

If, after your calculations, you fall "between 2 sizes", then the upper part of your body will be decisive in the choice of one size over the other. Indeed, the length of your trunk and arms will define the proper distance from the hanger or the handlebars. To do this, it's necessary to define your "APE index", which can be obtained by subtracting your size to your "arm amplitude" (length from the end of one arm to the other whith spread arms) . If the value obtained is greater than zero, you have to take the larger bike size and vice versa: take the smaller size if the value is less than zero.

How to choose a child's bike size?

Children bike sizes are defined by the size of the wheels. You will find a chart indicating the child size correspondences on our products. The first sizes start at 12 inches, including bicycles without pedals that are called dandy horse .

Children grow up very quickly and some parents tend to choose the biggest bike in order to prolong its durability, however, we strongly discourage this practice because the child may be afraid of a bike too big for them and quickly become discouraged. Their safety is also at risk.

> Read our complete tutorial to choose the size of a child's bike

Choice of wheel size

Which wheel size to choose for your bike?

Since the birth of MTBs in the 80s, all bicycles have been delivered with 26-inch wheels. As of 2009, manufacturers have developed the standard 29-inch, then an intermediate standard, the 27.5-inch. But which one should you choose?

Choice of wheel size
  • If you prefer manoeuvrability and liveliness, we advise you to take a 26". Besides, these wheels being the smallest, they will also be the lightest.
  • If, on the contrary, you are looking for comfort and efficiency, we guide you towards the 29". In fact, because the tire section is larger, the tire's suspension effect will tend to erase the terrain's roughness. Moreover, the wheel's large diameter provides a reduced angle of attack (angle between the wheel and the ground), which makes you able to cross obstacles more easily. Finally, by rolling, the 29" wheels will generate more centrifugal force and will therefore be more stable than the 26" wheels. Besides, taller people will find geometries at their size more easily with these wheels. However, in order to obtain an equivalent stiffness, these wheels need to be heavier and will consequently have more inertia at recovery.
  • If you are don't mind compromises are looking for the best balance between manoeuvrability, comfort and performance, manufacturers have also thought about you by recreating the 27.5". Historically known in France as the 650B, this wheel standard was used in the past on recreational road bikes. It now equips a wide range of bikes among all manufacturers.

These tips are to be taken with some caution because your practice, your morphology, your level and the terrain are all parameters to be taken into account in the choice of your bike's wheels size. For example a bike with 29" wheels, that is to say a high centre of gravity, won't work at all for a small beginner.

Find the perfect position on your bike with the postural study

In this postural study, we are pushing the limits of traditional studies. At present, there are fewer than 5 bicycle shops in France able to provide this level of study.

You have access to the best static and kinematic postural studies with state-of-the-art equipment and high-end capture system.

We start with a completely customized static study. Then a complete study in rolling situation on our "CYCLE FIT".

The Trek Precision Fit study is the most complete, most evolutive, and most competitive offer on the market.

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