How do I find out if a bike fits me? The question is simple, the answer complex. Those who provide them are best advised to seek help from experts who can help quickly with experience and a trained eye. This article cannot provide a generally valid answer either.

That is why the press service bicycle explains a good dozen parameters that enable a basic understanding of the often overwhelming geometry tables of bicycles.We show you How to fit your bike

Wheel size

The wheel size is the diameter of the rim without the tire. For bicycles, sizes range from twelve inches for children’s bikes to 29 inches for mountain bikes. 

City bikes and touring bikes often have 28-inch wheels, but sometimes we can see Adventure bikes with 26 inch wheels too. Road bikes are mostly 28 inches, mountain bikes 26, 27.5 or 29 inches and folding bikes between 16 and 20 inches.

“A persistent myth is that adults drive 28s. On the one hand, the wheel size specifies a minimum frame size, so that, for example, 28-inch wheels cannot be used to build an ergonomically sensible bike for 1.60-meter people. On the other hand, the rediscovered wheel size 27.5 inches has resulted in an exciting alternative for all areas, ”explains Stefan Stiener from Velotraum.

Note: The purpose of the wheel is usually decisive for the size of the wheel. The body size determines the frame size.

Frame size and their ways of measuring 

The size of the frame, also known as the frame height, provides a clue when choosing a suitable bike. However, sizes such as S, M, L are not very informative; rather, one should pay attention to the information in centimetres. Often frame sizes are also given in inches (1 inch = 2.54 cm). However, the manufacturers’ measurement methods differ considerably.

“The frame height is usually measured from the centre of the crankshaft bolt along the seat tube to the top edge of the seat tube. Sometimes there is also information up to the upper edge of the top tube or seat tube nominal, ”explains Volker Dohrmann from the manufacturer Stevens. “To make it easier, we write all this information in our tables,” Dohrmann advises

A special case is so-called unisize frames, which can be found on folding, compact or cargo bikes. There is a particularly large adjustment range for the saddle and handlebars, which suits most people between 1.50 and 2 meters tall.

Seat height 

The seat height is measured in a similar way to the frame size: from the centre of the inner bearing along the seat tube to the upper edge of the saddle. The actual seat height determines whether you pedal ergonomically.

“If you sit too high, your pelvis tilts when you pedal. If you sit too low, the power development is suboptimal and the stress on the joints is high, ”explains Philipp Martin from Cannondale and adds:“ If you have your own seat height in mind, you can quickly adjust a new or a rental bike ”. 

Slight deviations from the seat height can cause shoes with thick soles, pedals, particularly flexible saddles or springy seat posts.

Frame length 

The length of the frame is an even more meaningful measure of the fit than the frame size. Because the latter can be varied slightly by seat height, while the frame length can only be adjusted to a limited extent with a longer stem or another seat post. People with long legs need a rather short frame and “seat giants” with a long trunk need a rather long frame in order to achieve the same sitting position. 

There are two dimensions for the frame length: The decisive dimension is the effective frame length, also known as the “horizontal top tube”. It runs horizontally from the centre of the head tube to the centre of the seat post. It is attached to the upper edge of the head tube. 

The second dimension is the top tube itself because on most bicycle frames the top tube drops more or less strongly towards the rear. The top tube is only horizontal on classic bikes.

Stack and Reach 

These two neutral sizes indicate how much space the cyclist actually has in the frame. They form a right angle: the stack is measured vertically from the centre of the bottom bracket and Reach is measured horizontally from the centre of the top edge of the head tube.

“In this way, regardless of the seat angle (reach) and wheels, stem or handlebars (stack), you get directly comparable size information for frames and superstructures – which is why stack and reach have become more and more important for sporty bikes in recent years, in the information from the manufacturers and the tests the magazine, ”says Marc Jersch from Haibike.

Standover height 

The standover height is one of the dimensions on a bicycle with a directly illuminating benefit. The lower the height, the more step clearance the bike offers. It is measured from the ground to the top edge of the top tube in the middle – which is why it is only used on the classic “men’s bike”, while on the classic “women’s bike” it is used to mount and dismount deep top tube can be simplified.

In a direct comparison of standover height and inside leg length of the driver, you can see whether you can simply stand over the bike. This is necessary if you dismount while stopping or have to jump out of the saddle in a dangerous situation.

Elevation of the saddle 

An elevation of the saddle is found on most sports bikes – it indicates the difference in height between the saddle and handlebars. The greater the saddle elevation, the lower the handlebars and thus the more athletic the posture on the bike. Its opposite is the handlebar elevation, which is found on more comfortable bikes, as it puts the upper body in a very upright position.

Seat triangle, seat position and type of rider 

The seat triangle on a bicycle describes the relationship between the three points of contact between the rider and the bicycle: handlebars, saddle, pedals. “The alignment of this triangle is a clear feature of different types of bike,” explains Daniel Gareus from the Franconian importer Cosmic Sports.

“On the triathlon or time trial racing bike, for example, the triangle is turned very far forward: the saddle is directly above the crank and the handlebars are sometimes halfway between them. The result is an athletic-aerodynamic seating position with an almost horizontal back. ” 

On the cruiser, however, the triangle is turned far back: “The handlebars are much higher than the saddle and the crank is very far forward, almost under the handlebars,” Gareus continues. The seat triangle shows, among other things, the weight distribution on the bike: while on a Dutch bike almost all of the weight is on the saddle when the seat is very upright, on a racing bike it is much more evenly distributed over all of the three contact points.

The seat triangle is largely determined by the frame and can be changed to a small extent by components: a higher handlebar, for example, or a cranked seat post can help to adjust the seat triangle.

Seat angle 

The seat angle is a value from the seat triangle, the angle of the seat height to the horizontal is indicated. The flatter the seat angle, the further behind the bottom bracket the cyclist sits and the more weight is distributed on the rear wheel. Flat seat angles can be found on Dutch bikes and cruisers.

The steeper the angle, the further the saddle is above the bottom bracket and the more bodyweight you use to pedal. The steep angle is found on time trial bikes and modern MTB geometry, where it favours the central position on the bike and provides traction when climbing. “You can influence the seat angle within certain limits by moving the saddle in the clamp of the seat post, or switch between a cranked and straight seat post. In this way, the ergonomics of pedalling can be adapted to the individual length of the thigh, ”explains Stefan Stiener.

Wheelbase 

The distance between the two-wheel axles provides information about the smoothness or agility of a wheel. The longer the wheelbase, the quieter and possibly more sedate the bike and the higher the traction. The shorter the wheelbase, the more agile, playful and also more nervous the driving dynamics.

Rear-end 

The rear part of the wheelbase, so to speak, is measured from the rear end length from the bottom bracket to the rear axle. “When designing sporty bikes, attention is often paid to the rear end being as short as possible so that the bike feels nimble,” says Anja Knaus from the e-bike builder Flyer. Since this is at the expense of traction, especially on steep climbs, there are now also mountain bikes with a slightly longer rear end.

Stem length and handlebar width 

The dimensions of the components in front of the frame naturally have a decisive influence on the seat geometry. Not only the length and the angle of the stem are to be mentioned.

“The shape of the handlebars also makes a big difference,” says Markus Riese from Riese & Müller: “While city bikes often have cranked handlebars, racing handlebars are up to ten centimetres beyond the stem.” Mountain bikes have been around for a few years have seen the trend towards shorter stems and wider handlebars, which offers significantly greater control over the front wheel.

Bottom bracket height (also: bottom bracket height) 

The height of the bottom bracket above the ground has a decisive influence on the riding dynamics of a bicycle. “The deeper the warehouse, the better the handling of the bike,” says Philipp Martin. However, it must still be possible to pedal the bike when cornering without touching the pedals.

Martin adds: “On off-road bikes with suspension, the bottom bracket is lowered even further by the compression.” But since you don’t want to get stuck with the pedals, especially on uneven terrain, the bottom bracket of an MTB will always be higher than that of a racing bike.

Since the inner bearing height also depends directly on the wheel and tire dimensions, the value of the lowering of the inner bearing (often called “BB drop”) must be taken into account.

Many paths can lead to the right bike 

Bicycle geometry and ergonomics are a difficult interplay of many factors. The balance between the various aspects makes a good and suitable bike. Most people get along well with “off the shelf” bikes. Others are more sensitive and have to change a lot of settings before the bike fits.

Good specialist dealers advise their customers until the right saddle, grip or stem is found. “The more time you spend in the saddle, the clearer it becomes whether a bike fits,” says Stefan Steiner. “Frequent riders such as cyclists and cyclists can therefore have their measurements taken at the specialist retailer – you can already tell from the length of the torso, crotch and arms.

Last but not least, people with extreme needs, very specific ideas and a desire for exclusivity also have the option of having a frame made to measure.

What´s next?

It is really important if you are going to spend many our on the saddle to consider doing a bike fit, especially if you suffer with any physical condition that can be agraviated.

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