The bike frame is the core component of the bicycle, onto which the handlebar, wheels and other components are fitted. The design of most modern bike frames originates from the safety bicycle of the late nineteenth century. The two wheeled bike was marketed as the safer alternative to the large wheeled penny farthings of the time, and ultimately came to supplant them entirely.
The modern bike frame consists of a number of tubes connected together in such a way as to provide the greatest amount of strength possible. Bicycle frames are available in a number of different designs and materials, and all can be found on the eBay shopping platform; whether it is a mountain bike, BMX or other bike.
Types of Bicycle Frame
The design of the bicycle frame is based on the shape and positioning of the tubes.
What is a bike frame?
- The head tube, to which the handlebar is fitted. This also connects to the fork, which holds the wheel and allows the cyclist to steer the bicycle.
- The top tube, which connects the head tube to the seat tube.
- The down tube, which connects the head tube to the bottom of the seat tube. It is on this tube that accessories like bottle cages are often placed.
- The seat tube is where the seat post is connected to. By changing the amount of the seat post that is inserted into the seat tube, it is possible to change the height of the seat.
- The seat stays connect the top of the seat tube to the rear wheel fork.
- The chain stays run alongside the bike chain, connecting the bottom of the seat tube to the rear wheel fork.
What Bike Frames are Available?
The diamond frame is overwhelmingly the most commonly available design of modern bicycle frame, with most other designs being variations. The diamond frame consists of two triangles. The larger front triangle connects the seat tube, head tube, down tube and top tube. The rear, smaller triangle consists of the seat tube, seat stays and chain stays. The geometry of this design offers a good deal of structural strength, while minimising the amount of materials required, meaning less weight. The wide availability of this frame means that it is one of the most affordable kinds of frame.
Another popular kind of bike frame is the step through. Originally designed so that women wearing skirts would be able to more easily dismount, this kind of frame has its top tube placed lower on the frame, and sometimes does not have one at all. The added space makes it easier for the user to mount and dismount the bike, as well being potentially safer as the cyclist can step through the frame without becoming caught in it in the event of lost balance.
The cantilever frame is another design. It is very similar to the diamond frame, with the exception that many of the tubes are curved. There is often very little difference in strength and rigidity between the cantilever frame and the diamond frame, the key difference being aesthetic.
The design diamond frame itself often varies depending on the kind of bike it is intended for. For more specialised bicycles, there are a number of variations of the diamond frame.
The road bike frame, designed for road racing bicycles, offers two variations. Traditional geometry diamond frames are generally seen as more comfortable and stable. The longer ‘wheelbase’, the horizontal difference between the centre of the front and back wheel, contributes to shock absorption and enhances comfort. The compact geometry diamond frame offers a lower centre of gravity. This, combined with a shorter wheelbase and smaller rear triangle, gives the bike more responsive handling.
Designed for the indoor racing track bicycle, this kind of frame has a steeper seat tube, placing the cyclist in a more aerodynamic position.
Utility Bicycle Frame
This kind of frame is built for comfort, with a seat tube that is angled to offer a comfortable, more upright, riding position.
Due to the rough terrain that these frames are intended to handle, many of these frames come with shock absorbers. This can, however, mean these frames are more expensive.
Due to its wide availability and relative simplicity, the diamond frame is the easiest to find and affordable option when it comes to bicycle frame design.
Bicycle Frame Materials
Historically, bicycle frames have been made out of all kinds of materials, from bamboo to magnesium. Modern frame materials are chosen for their strength, weight and crash worthiness. A bicycle frame should be constructed from a light, strong material that can withstand crashes as well as withstand the daily stress of use.
Steel has long been used in the construction of bicycle frames. Though specific price depends on the kind of steel used, these frames are generally some of the least expensive available. Steel frames are very strong and more resilient to crash damage, as steel can be bent without losing its strength.
These frames can also offer more comfort for the cyclist, as they often have a level of flexibility which provides some shock absorption, making steel frames more suitable for riding over rough terrain. Steel frames are often built with smaller tubes, which some cyclists find more aesthetically pleasing. However, steel is denser than other available frame materials, meaning such frames are often heavier. There is also the possibility of rust, though this can be prevented with anti-corrosion treatments and paint.
While the cost of aluminium is generally slightly higher than that of steel, it offers a second choice for a cyclist looking for an affordable frame. Many new frames and bicycles are made out of aluminium, meaning that such frames are widely available. Aluminium has a better strength to weight rating than steel, meaning that such frames can be made lighter while maintaining strength.
While the lack of flexibility in many aluminium frames can make rough ground cycling an uncomfortable experience, if a cyclist intends to cycle on smooth surfaces such as roads or cycle paths, this becomes less of an issue. Furthermore, some cyclists prefer the more rigid feel of an aluminium frame. While aluminium frames suffer from fatigue somewhat faster than steel frames, lasting five to ten years, they do not suffer from vulnerability to rust.
Carbon frames are an unusual, but increasingly popular choice for frame material. These frames are made of carbon fibre, a material that is light weight and strong, as well as being resistant to corrosion and easily formed to any shape needed. This is offset by the fact that carbon fibre is a brittle material, and there is a higher chance of the frame cracking under the strain of a crash than other materials. For this reason, carbon frames are designed to bend, and the material allows the frame to be bent back into shape without losing its strength. Carbon frames are however, among the most expensive available, putting the price range of these kinds of frames significantly above that of the more widely available and easily produced aluminium and steel varieties.
Sizing a Bicycle Frame
As with many bicycle components, correctly sizing the bicycle frame to the cyclists is important for both riding comfort and safety. A rider faces a greater risk of crashing when struggling to ride a bicycle with a frame that is too big or small for them.
- The measurement used to fit a rider to a correctly sized frame is the ‘bicycling inseam’. This is a shorter measurement than the trouser inseam, and is measured from the bottom of the rider’s crotch to the floor.
- This measurement should be compared to the seat tube length of the frame, which is generally available on the item’s entry. A 54cm size frame, for example, means that the tube measures 54cm from where the pedals will be installed to the top, where the seat will be fitted.
- Generally, there should be a few inches space between the top of the frame and the rider’s crotch; more if the frame is intended for use over rough ground. Components like the seat can be adjusted to suit a rider’s height more comfortably.
- Sometimes manufacturers measure their frames in differing ways, so it can also be a good idea to refer to the item’s entry, or the manufacturer’s webpage for further information regarding sizing.
Finding a Frame on eBay
There is a wide selection of bicycle components on eBay, including bike frames of various materials and designs. The first step to seeing the listings of available bicycle frames is to navigate to the Sporting Goods portal, and then the Cycling Section. Bike frames can be found under Bike Parts. Here it is possible to browse the entire listing of bike frames, and these can be arranged by item condition, distance to the seller, the amount of time the item has been listed or by price. It is also possible to filter the frames displayed by material, or by the type of bike they are designed for, as well as by condition and brand.
Key information about the frame, such as the material it is made of, will generally be clearly displayed in the item’s listing, making it easy to see whether a particular frame matches the desired requirements quickly and easily. More information will also be available on the item’s page, along with information about the seller such as reviews and feedback ratings, allowing a purchase to be made in confidence. It is also possible to ask the seller a question about the item.
If a specific kind of frame is required, it may be easier to use the eBay search function, available at the top of every page. This can be the easiest, fastest way to find a particular item. The Search Tips page offers further information on effectively using eBay’s search function.
The bicycle frame makes up the centre of a bicycle. A well-made frame of the right material is important to both the comfort of the rider, and their safety. The quality of the frame can also have a great impact on the longevity of a bicycle, against corrosion, crashes and the general strain of use. Finding the right bicycle frame is important, and eBay offers an accessible, wide range.