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This frame size and frame geometry is what you need for a mountain bike


Who wanted to buy a bike in the past, usually went to the nearest bike store. The bike, whose optics could convince the most, was test-sat. The only quality criterion was often whether you could still reach the ground with the tips of your feet. Today, most people know that there is the so-called stride length, which should provide information about the appropriate frame size. Whether road bike, city bike, cross bike, trekking bike, cyclocross or gravel bike, BMX or mountain bike: the body's own stride length gives a good first indication of the optimum frame size, regardless of the type of bike. Especially for MTB, many manufacturers are trying out different frame geometries. The frame geometry influences the range of use for which the MTB is suitable. It is therefore worthwhile to also take a look at different dimensions of the frame before buying. Depending on the main area of use, the geometry of the bike frame determines the driving behavior. So each area of use needs a slightly different shape. To find the right frame height for your dream bike, you can find all the important information here.

  1. What frame height do you need for a mountain bike?
  2. How do you measure your stride length?
  3. Tips for frame geometry

1. What frame height do you need for a mountain bike?

First of all, frame height and frame size mean the same thing. As a rule, the "centre-to-top" method is used to measure from the centre of the bottom bracket to the end of the seat tube. The resulting frame height is given in centimetres or inches. Many manufacturers nowadays give the frame size in S, M or L, just like clothing sizes. Major brands such as Cube, Santa Cruz, Cannondale or Trek have years of experience and provide reliable reference values. Body size ranges are given for the respective specifications. Information on the respective stride length is also often given. All this gives you a first indication of which bike fits your body. You should really pay attention to the specifications of the respective manufacturer. Sizes can differ between brands due to manufacturer-specific construction methods and are difficult to compare. If you were satisfied with a frame size M on your last bike, you cannot simply transfer this to another model. 

The right size has an influence on the riding performance of the mountain bike. The right fit will give every rider even more fun, control and comfort. A smaller frame will feel more manoeuvrable. This will benefit you on technically demanding trails with switchbacks. If you choose a larger frame, the bike will behave more smoothly. It is more comfortable on fast downhill rides where obstacles are rolled over generously. Unlike other types of bikes, it is important that there is plenty of space between the top tube of the frame and the rider's crotch. Regardless of whether you are riding a hardtail or a fully: when riding downhill, situations often arise in which you should be able to swing off the MTB quickly. This distance between the top edge of the top tube and the crotch is called the overhang. It cannot be compensated by retrofitting other components. If the top tube is already jammed between your thighs the first time you get on the bike, the frame height is too small or the bike is generally unsuitable for your body. The fact that the inseam length and height can only serve as a guide to finding the right size is also due to the fact that bodies have individual characteristics. Some people have particularly long arms, torsos or legs. It can happen that someone's height indicates that they should ride a smaller frame height, but their particularly long legs suggest a larger frame. By the way, frame height is not usually specified for children's bicycles. Instead, the wheel size in inches provides information. Children's bikes are often advertised with age information as a recommendation for the right size.


2. How do you measure the stride length?


Simply determine the stride length yourself. To do this, you'll need a tape measure or folding rule and a loose saddle, level, or book. Stand in front of a straight wall. The legs should have a small distance. In the crotch you now clamp the book or the saddle. Measure from the tip of the saddle to the floor. In the case of the level or the book, it is measured from the top of the book or the level to the floor. The step height determined in this way can be calculated into the correct frame size. To do this, multiply the stride length by a factor of 0.574. A value between approx. 35 cm and 56 cm should be the result. Alternatively, you can of course go to a bike store and get professional help with measuring.

Body heightFrame height in inchesFrame height in cm
155 – 165 cm14 – 15″35 – 38 cm
165 – 170 cm15 – 16″38 – 41 cm
170 – 175 cm16 – 17″41 – 43 cm
175 – 180 cm17 – 18″43 – 46 cm
180 – 185 cm18 – 19″46 – 48 cm
185 – 190 cm19 – 21″48 – 53 cm
190 – 195 cm21 – 22″53 – 56 cm
195 – 200 cm22 – 23″56 – 58 cm


3. Tips on frame geometry

Tipp 1 - Determine the desired area of use:

Before purchasing a new mountain bike, it is important to think about the main area of use. This requires an honest look at the previous riding behaviour. This provides information about which type of MTB with which geometry fits best. If you like to ride long tours uphill and downhill without riding trails with deep drops and wide jumps, you can buy an MTB hardtail. Fullys are designed to overcome larger obstacles. All-mountain or trail bikes are real all-rounders and are fun to ride on long distances as well as on rougher trails. Enduro bikes cushion even more jumps and are somewhat more adapted to downhill riding. Freeride and Downhill bikes roll over large scree without any problems, riding uphill is rather nothing for these models. If you are happy to do without the shuttle service but still want to race down trails several times in a row, you can consider an e-mountain bike. Reaching high places with great views can also be made easier with the help of an e-bike. These considerations about the area of use are very profitable. Depending on this, the geometry of the frame changes and with it the seating position. The desired riding position can also help you decide which bike is right for you. So also consider whether you want to ride long tours and therefore prefer to sit upright. Frequent visits to the bike park require a different seating position. A detailed look at the measurements will help you to assess the handling of your new bike. You can find more details about mountainbike types here.


Tipp 2 - Consider the stack to reach ratio

If you want to take a closer look at the frame geometry, you should remember a few terms. One of these is the stack to reach ratio. It provides a good insight into the riding position you will have on the bike. Stack means the distance from the highest point of the top tube to the centre of the bottom bracket. The stack therefore indicates the height of the front of the MTB. The higher it is, the more upright the position when standing and sitting. The reach is the distance between the centre of the bottom bracket and the handlebar. A longer reach therefore leads to a longer wheelbase. People with long torsos or arms can benefit from frames with a long reach. In general, the reach says something about how tall the frame is. A smaller reach leads to more manoeuvrability, a larger reach provides more stability. When mountain biking, you often stand on the pedals, especially when going downhill. A long reach leads to a sportier posture, a shorter reach leads to an upright posture. The reach should not be confused with the effective top tube length. The top tube length is the distance between the centre of the head tube and the centre of the seat post. The top tube length can be adjusted with the help of the seat post or a different stem if, for example, you experience discomfort when pedalling. Since it is not possible to compare the sizes given by the manufacturers, a comparison of the top tube length is a better option. Caution is advised here, as the top tube length changes with the seat tube angle. The reach always has the perpendicular to the bottom bracket in full focus and is therefore more meaningful. The wheelbase, in conjunction with the steering angle, influences whether the bike is manoeuvrable or smooth-riding. The wheelbase is the distance between the wheels measured centrally. The steeper the steering angle, the more manoeuvrable and playful. The flatter the angle, the smoother the ride. A flat angle is particularly suitable for fast downhill rides where technique plays a subordinate role and obstacles are more likely to be rolled over than avoided. This is why flat steering angles are particularly popular for freeride and downhill bikes. All-mountain and trail bikes tend to use steeper steering angles, for example, in order to be able to steer around tight bends better. 


Tipp 3 - Don't forget the wheel size!

Besides the frame geometry, the wheel size is also relevant. Whereas in the past you mainly found 26" wheels on mountain bikes, today 27.5" or 29" dominate. Larger wheels make it easier to roll over obstacles. 27.5" wheels are mainly used on bikes with XS or S frame sizes. They bring a playful, agile behaviour and can be advantageous on technically challenging trails. Instead of 27.5", we often speak of so-called 650B wheels. This is the French term. The most popular wheels today are 29". They roll over scree without any problems, are smooth-running and provide stability and grip. Fast trail descents are particularly fun with them. By the way, there are also so-called Mullet bikes. A 29" wheel is mounted on the front and 27.5" on the rear. This is supposed to combine the advantages of both sizes. This also changes the geometry, the front of the bike moves upwards and the steering and seat angles become flatter. It's best to try out the Mullet bike when you get the chance to see if it suits your riding style.

In summary, you can follow the same procedure: Determine frame height based on body size and stride length, define range of use, view geometry. This way you are on the safe side even when buying second-hand bikes online or ordering from a dealer, without having to test ride. In the end, no matter how perfectly the bike fits, it is first and foremost the rider's skills that make every outing an experience. So rather than getting too lost in the science behind a frame, get on the saddle and get going. Buycycle offers a variety of used mountain bikes from top manufacturers. If you have any questions about the right frame height, the buycycle team will be happy to help.



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