How do I choose a bike frame

Bicycle frame is the same as a bicycle frame?

By: editorial staff VIS product safety

Different frame types

Even a cursory glance at the adjacent picture reveals that this is probably not the case.

Why are there so different frames?

In order to be able to answer this question, we must first be clear about the function of the framework.

Function of the frame

The frame bears the rider's weight and transfers it to the wheels. We could call it the skeleton of the bicycle that carries all of the bike components (e.g. steering, saddle, etc.).

Its design and the components used have a significant influence on the break resistance, as well as

  • Smoothness and
  • Manageability.

All questions that can be summarized under the heading "driving behavior".

Driving behavior

As already mentioned, the frame used has a direct influence on the handling of your bike. Straight-line stability, vibration behavior and agility (steerability) are affected.

It would certainly be great if it were possible all mentioned requirements optimal to design; However, this is only possible to a limited extent (... a wheel without steering would have the best straight-line stability ...).

So: the There is no such thing as an optimal bike for every purpose the there is no optimal ski. The frame selection must therefore be based on your needs and so you should ask yourself a few questions:

Determination of the appropriate type of bike

  • For which main area of ​​use should the bike be suitable (e.g. sport, travel, shopping, beer garden, ...)?
  • In which terrain (gravel, tar, plain, mountains, ...) do you predominantly move?
  • Do you place more value on comfortable, fatigue-free sitting or do you want to achieve top athletic performance?
  • Do you want to take heavier luggage with you?
  • Does the bike have to have a deeper step through?

Types of bicycles

As a rule, a certain type of bike will emerge from the individual answers:

The types of bicycle mentioned often have very different designs or frame geometries; that is, we sit very differently on these types of bike.

Sitting position

Only those who sit properly can work properly; The correct sitting position is very important both in everyday office life and when cycling. The saddle and handlebars must be adjusted correctly, but your preferred posture must also be taken into account.

If the basic positions are not correct, this can lead to considerable discomfort in the shoulder, neck and back area as well as in the knee area.

In order to enable an individually correct setting of the saddle, handlebars, etc., the frame geometry must be suitable for you. For example, imagine the frame is so short that your knees touch the steering or limit the steering angle. The risk of falling would increase significantly.

Frame geometry

Trapezoidal frame geometry

The frame geometry is not only responsible for the seating position. In addition, the frame geometry sets the course for whether the bike is the best possible Driving safety guaranteed.

Frame breaks are not only due to material problems, the geometric design also indicates safer - e.g. B. in the form of a diamond frame (Trapezoidal shape) - and less secure designs.

Frame geometry:

Inclination, arrangement and position of the individual pipes to one another and their spacing. These factors influence, among other things. the straight-line stability as well as the steering behavior and thus the driving safety.

Favorable and less favorable frame geometries


Diamond frame

The so-called diamond frame is often found; The triangular design of the rear end and the trapezoidal design of the front end are referred to as diamond. This geometry is to be regarded as very stable.

In the comfort sector and in the women's bicycle sector, a slightly modified trapezoidal design has become established, in which the top tube is lowered towards the seat tube.

The deeper step-through makes it easier to get on.

The number of these different comfort variants is large; The so-called Anglaise frames and Mixte frames have proven to be particularly stable species.

On both frames, the lowered top tube is extended to the hub of the rear wheel. With the Mixte frame, the top tube on the seat tube does not combine to form one tube, but is instead continuously separated all the way to the head tube.


Anglaise frame


Mixte frame

The weighing frame has proven to be a somewhat less favorable form of construction. Since there is an interruption in the trapezoid in the area of ​​the seat tube. The forces occurring here under heavy loads can lead to the loaded seat tube being damaged.


Cradle frame

Stability and durability

Note: In the context of this sub-item, the effects of the various materials (steel, aluminum, composite materials) on the frame construction were not discussed; In this context, note the article "Buying a bicycle".

It goes without saying that if the frame breaks, serious accidents are usually unavoidable.

Frame tubes last a particularly long time if they are only subjected to tensile or compressive loads in the longitudinal direction; On the other hand, they are sensitive to lateral bending loads. Accordingly, the aim of a safe geometry must be to avoid the bending loads.

The frame construction distinguishes between zones subject to bending stress (e.g. in the area of ​​the bottom bracket) and so-called neutral zones (mostly front and rear).

In this context, please note that brackets (e.g. protective plates) may only be soldered or welded on in the neutral areas.

Danger: Under no circumstances may independent Drill holes on the frame - but also on other bicycle parts (e.g. handlebars), for example to attach an additional cup holder! The voiding of your warranty is more of a minor problem that you may face. Rather, frame breaks and the associated serious fall accidents are to be feared!

The weight distribution between the front and rear wheels has a major influence on driving behavior. Just think of the "stunts" of cool bikers who only do some laps on the rear wheel. However, if you want to refrain from doing this, you should aim for a "moderate" distribution of the burden.

Load distribution between the front and rear wheel

We should make one fundamental fact clear to ourselves: the front and rear wheels bear the weight of the rider, the wheels transmit the drive force (rear wheel) and control the wheel (front wheel).

Depending on how this load ratio is designed, the driving characteristics change. Not only the "on-site" starting positions are decisive, but also how we sit on the bike (driving position).

If we position ourselves very far back on the saddle and, for example, straighten our upper body, the center of gravity of the load moves towards the rear wheel.

Focus on the rear wheel

A higher load on the rear wheel leads to an optimized (drive) power transmission; at the same time, the load on the front wheel decreases synchronously. If the load on the front wheel is too low, the friction between the tire and the road is too low. The steering reacts very spontaneously and the bike tends to oversteer; In addition, the directional stability decreases and the bike tends to break out of the way when cornering. Here, too, there is a risk of falling!

Focus on the front wheel

The further we move forward on the saddle and the lower we crouch over the handlebars, the more the center of gravity moves towards the front wheel, the more stress is placed on it.

Steering becomes "more difficult", more force has to be used because the friction between the tires and the road surface increases. This can mean that we are always a little "late", the vehicle tends to understeer. Since the load on the rear wheel is reduced at the same time, it can happen that the drive wheel "spins" in steep passages, especially on gravel roads.

In addition to the positions we take on the bike in different ways, the driving behavior is also influenced by the structural conditions of the frame and the components connected to it.

The wheelbase is an important factor.

wheelbase

Long wheelbases (e.g. 110 cm) - as are typically found on touring bikes - ensure good straight-line stability and lead to smooth driving behavior.

In contrast, short wheelbases (less than 100 cm) increase agility. This is e.g. This is important, for example, on racing bikes, as quick reactions are required when riding in large groups in order to avoid collisions.

How is the wheelbase calculated? Put simply, we could say that the wheelbase is defined by the frame size and the front and rear length.

Front length

The front length defines the distance between the bottom bracket and the front wheel axle.

Rear length

The rear end defines the distance between the bottom bracket and the rear wheel axle.

Effects

By using different lengths of the front and rear ends, the frame geometry can be further adapted to your requirements.

Example: With a triathlon bike, the triathlon handlebars achieve a very flat body position that is pulled far forward. As mentioned above, however, this means that there is a lot of understeer. The use of a long front length reduces the load and understeer is less.

Example: If you choose a very short rear end, for example, you will improve the climbing behavior of your bike. At the same time, however, this can mean that the front wheel lifts off when pedaling hard on an ascent and the driver is in danger of falling (so-called "sitting down over the rear wheel"). He must therefore try to counteract the rise of the handlebars by pulling the body forward in a particularly flat position. However, this position is somewhat exhausting.

So you can see that an advantage in one place can result in a disadvantage in another. It is your job and that of the specialist trade to find the ideal compromise between sporting objectives, comfort and the best possible driving safety.

Steering head angle

Another feature of the frame geometry is the Steering head angle (see yellow arrow, picture opposite), which often moves in a range between 71 and 73 degrees.

impact

The steering head angle has a great influence on the steering force. Steeper steering head angles generally lead to more easily steerable wheels, but the handlebar flutter also increases as the front wheel vibrations are less dampened by the wheel fork, which is then usually also more steeply positioned. The lower steering precision can lead to an increased risk of accidents.

If you want to buy a touring bike, you should look for a bike with a steep steering head angle of 73 degrees or a little more. This does not have a negative effect here, as these bikes are usually very heavily packed; one consequence is the reduction of the handlebar flutter.

At particularly flat angles - such as the Dutch bike has (approx. 66 degrees) - the weight of the driver when steering is negatively noticeable when driving slowly. Since the handlebars react very slowly, this can lead to accident situations, especially in city traffic, if you cannot avoid an obstacle in time.

Front fork

It is very popular in "cycling circles" to replace the front fork.

This is often done to replace an unsprung fork with a sprung fork; The main reasons here are greater convenience and security.

Quite legitimate and fundamentally positive thoughts. But is something like that really possible? Can any fork be used?

The question could be answered with a clear answer "Yes indeed but ..."

In order to be able to assess whether an exchange fork is suitable, we have to deal with an interesting aspect of vehicle construction, the so-called caster.

trailing

We keep observing the caster of a wheel without perhaps paying much attention to it.

If you want to take an example, think of the baggage cart and the shopping trolley.

On these vehicles, the wheels automatically align to the rear when the cart is pushed forward.

& and anyone who has ever caught a shopping cart with the wheels not pointing backwards will have noticed that "navigation" through shelves and displays has become very difficult, if not impossible.

The caster on the bike is not so obvious, but it also comes into play here.

definition

In the case of caster, the wheels are offset from the joint axis or the axis of rotation of the head tube.

In order to be able to recognize the trail, the axis of rotation (blue arrow) must be extended to the ground.

If a perpendicular (red arrow) is now drawn from the front wheel axle to the ground, it can be seen that this strikes behind the extended axis of rotation.

The distance to be measured in cm defines the caster (green arrow) of the bicycle.

In practice, with a caster of approx. 6 cm, mostly good steering properties, especially not too restless, can be achieved, which are very important for driving safety.

Note:
Touring bikes often have a smaller (5 to 5 ½ cm) trail. Due to their long wheelbase, these bikes usually run quite smoothly. In order not to further increase the inertia of the steering, the caster is slightly reduced.

Effects

Changes to this "factory" defined or specified caster can cause your bike to have different handling characteristics.

In extreme cases, this can mean that your bike can no longer be driven if it comes out of a caster leader becomes. This could happen if, for example, a fork that was bent sharply forward was built into a steep steering head.

Danger situation

A wheel that is in the state of Forward is located, tries to "turn around" in order to get back into a "follow-up position".

So it would always break out to the left or right and the bike would no longer be steerable; Basically, it goes without saying that this reduces driving pleasure and increases the risk of accidents.

Please note: Especially when replacing the front fork, the curvature of the fork must always be seen in relation to the steering head angle.

If you have now selected a frame geometry that is suitable for you from the analysis of your personal requirement profile, you should now start to adapt the frame to your body dimensions. It has to be the right one Frame size be chosen so that, among other things an optimal power transmission and seating position is guaranteed.

Riding a bike is much easier overall and is simply more fun. ... and it will also happen less often that other cyclists pull past you without it looking like a great effort. In addition, misalignments can be prevented, which can sometimes lead to chronic damage to health.

What frame sizes are there?

The sizes given by the various manufacturers can only be compared to a limited extent. Since there are no measuring regulations, the frame height is usually specified. The respective dimensioned sketches from the manufacturer provide precise information.

Rule of thumb:

Frame height =
Distance from bottom bracket shaft to seat clamp

The most common units are inches or cm, where 1 inch (") is 2.54 cm, so a 19" frame is equivalent to a 48 cm frame.

As already mentioned, the frame geometry varies depending on the purpose of the bike
z. B .:

Step height

About the step height (Inside leg length) you can determine which frame height is right for you:

Step height = determination of the frame height.

Measure your step height barefoot, with feet hip-width apart (see sketch).

The table below shows how you can use this to calculate the correct frame height for your type of bicycle.

Effects

Bike type

Step height
multiplied by factor

Frame height in

Mountain bike

0,226

inch

Trekking bike

0,265

inch

Racing bike
City bike

0,665

cm

Example: Step height = 86 cm

Mountain bike frame height = 86 x 0.226 = 19.43 inches

Trekking bike frame height = 86 x 0.265 = 22.79 inches

Frame height racing bike = 86 x 0.665 = 57.19 cm

If the theoretical value is between two frame sizes, the following rule of thumb applies:

  • For a sporty riding style, choose the smaller frame height.
  • For touring-oriented riding, choose the larger frame height.

Optimal seat height

The seat height of the saddle must be set correctly in order to develop the optimum efficiency of your "muscle fat".

To adjust the saddle height, the clamp on the frame is released and the saddle adjusted as required.

First, lower the left pedal (6 o'clock position). Sit straight on the bike and place your heel on the pedal.

The saddle height is correctly adjusted when the left leg is extended in this position (Note: Sit up straight and don't let your pelvis hang sideways!). The seat post may only be pulled out as far as the marking in order not to impair the breaking strength of the post. If there is no marking, the support must be at least 6 cm deep in the frame. Then tighten the clamp again.

Broken, improperly secured seat posts are one of the most common dangers; Falls can usually no longer be avoided!

Inclination of the saddle

The connecting line from the rear of the saddle to the tip of the saddle usually forms a horizontal line. However, if you get pubic bone pain while cycling, you should lower the tip of the saddle a little. They then sit mainly on the pelvic bones and thereby relieve the pubic bone.

The tip of the saddle should be 6 cm - 8 cm behind the center of the bottom bracket. For a cross check, the kneecap is exactly perpendicular to the pedal axis when the crank is horizontal (3 o'clock position).

Adjusting the handlebar height

The handlebar height is changed by raising or lowering the stem. In the stem you will find a marking line that shows how far the handlebar post can be pulled out. An angle-adjustable stem enables variable adjustment of the handlebar height, as the angle of inclination can be set individually.

The handlebars are a particularly sensitive area because the cyclist leans on them on the one hand - breaking away could lead to a forward fall - and on the other hand, it must be ensured that the bicycle can be steered.

Tip: When driving, always bend your arms slightly at the elbow joint, your arms can then work like "shock absorbers" and thus reduce health problems caused by vibrations and shocks.

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