Key knowledge and maintenance strategies of bicycle frames

The vehicle frame plays a crucial role. It not only supports and connects the vehicle's various assemblies, ensuring they remain in their correct installation positions, but also bears various internal and external loads. Therefore, the frame must possess sufficient strength and rigidity to effectively withstand the vehicle's weight and the impact forces transmitted from the wheels.

The frame is usually ingeniously constructed of two longitudinal beams and several cross beams, and is cleverly supported by the suspension device, front axle and rear axle to steadily carry the wheels.

Vehicle frames can be categorized into perimeter frames, backbone frames, ladder frames, and truss frames based on differences in their structural forms.

Perimeter frames are often used in large sedans due to their unique design. They feature a widened center section, lack crossmembers, and typically feature closed-section components. This design not only reduces the floor height, thereby increasing the passenger compartment area, but also simplifies the structure, making manufacturing easier.

A backbone frame is based on a central longitudinal beam that runs through the entire vehicle. The beam can be tubular or box-shaped in cross-section. While lightweight and possessing excellent strength and rigidity, it requires high manufacturing precision and is relatively difficult to maintain and repair.

The ladder frame is carefully constructed from two longitudinal beams and multiple cross beams. The cross-section of the longitudinal beams can be diverse, such as channel, Z-shaped or box-shaped. This type of frame exhibits excellent bending strength, while its parts installation process is both strong and convenient.

The truss frame is constructed through the ingenious combination and welding of steel tubes. It has excellent rigidity and lightweight design, but the manufacturing process is relatively complex and the cost is high, so it is mainly used in the racing field.

The subframe does not belong to the vehicle's frame structure. It plays a supporting role to ensure that the axle and suspension can be smoothly connected to the "main frame".

Causes of frame breakage

External Factors

A vehicle frame may break or deform due to a variety of factors. First, the vehicle may be involved in an accident or external impact while in use, causing severe physical damage to the frame. Second, long-term use and lack of maintenance can cause the frame to gradually wear, corrode, or deform. Furthermore, the design and manufacturing quality of the frame are key factors affecting its durability. If the frame has design flaws or poor quality control during manufacturing, it may break or deform during vehicle use.

Design and Manufacturing Factors

1. When a vehicle travels on uneven roads, the frame is subjected to vertical impact loads. If this load exceeds the frame's allowable stress, it can cause frame fracture. Furthermore, when the vehicle travels uphill or downhill, turns, or is unevenly loaded, localized frame fractures may occur due to overload.

2. The frame design or attachments may cause localized torque, leading to frame fracture. For example, some frames have a smaller cross-sectional area at the front of the longitudinal beam. This, combined with the influence of the engine and transmission, results in a sparse distribution of crossbeams, which reduces frame stiffness. Under dynamic loads, the front of the longitudinal beam may fracture, particularly at the lower wing.

In addition, the frame may be affected by cantilever loads perpendicular to the longitudinal beams (such as the fuel tank, suspension and spare tire), which will produce localized distortion and become a potential cause of frame fracture.

3. When the vehicle is driving, if one side of the front wheel encounters greater resistance, the frame is prone to diagonal plane deformation.

4. When a vehicle is involved in a collision, the violent impact can cause frame deformation. This deformation alters the frame's geometry, affecting the relative positions of its components, deteriorating the vehicle's technical condition and potentially rendering it inoperable. This deformation typically occurs when the force acting on the frame exceeds its elastic limit. Once the force is removed, the frame cannot return to its original shape, resulting in permanent deformation.