A brief discussion on the transmission system

For amateurs, there may be a situation where the speed of the bike does not change much at a high cadence frequency. The reason is they don’t use the transmission system correctly. This article gives a brief introduction to the transmission system for amateurs.

1. Structure and Principle

The transmission system mainly includes the Gear Shifter, Gearbox and a Drive Train. The gear shifter exerts force to transmit the transmission command to the drive train. The drive train executes the transmission command during pedalling so that changing the front and rear gear ratios of the crankset and flywheel to achieve different riding speeds at the same cadence.

Drive Train

Drive Train

2. The type of transmission system

The transmission system includes the front transmission system and the rear transmission system. The front transmission system includes the front derailleur, crankset, crank, and the front shifter. Similarly, the rear transmission system includes the rear derailleur, flywheel, and rear shifter.

Transmission system

The front derailleur is mainly divided into four types which are top swing type, bottom swing type, E top swing type, and direct-mount type. 

The guide plate of the top swing derailleur swings on the upper side of the mounting ring. Based on the clamp position, the moving part of the top swing guide plate is located higher than that of the bottom swing derailleur. Except that, the connecting part of the top swing derailleur is shorter and the stiffness is higher so that the shifting speed is quicker than that of the bottom swing derailleur. 

The guide plate of the bottom swing derailleur swings on the lower side of the mounting ring. It is mainly used in bikes equipped with shock absorber systems and requires a higher front derailleur installation position, such as XC, AM, FR etc.

Top swing derailleur
Bottom swing derailleur

The E top swing derailleur is directly mounted on the bottom bracket. When installed on the bottom bracket, you need to use a matching crankset, which requires higher precision for the bottom bracket and crankset. Except that, compared with other derailleurs, it is more difficult to install and debug. 

The direct-mounted front derailleur is also called the ‘D’ derailleur. It is directly installed on the reserved holes or clamps of the frame. It is more convenient to install and debug and is commonly used in road bikes and luxury mountain bikes.

D derailleur
E Top swing derailleu

The rear derailleur is mainly divided into external derailleur and internal derailleur. According to the wire pull direction, the external derailleurs are divided into top normal and low normal types. Based on the length of the guide wheel bracket, they are long, middle, and short types. The advantage of the short derailleur is that can better avoid hitting the obstacles. The middle and long types can use a flywheel which with a larger number of gear teeth. 

The top normal rear derailleurs return the chain to the smallest sprocket on the cassette when no cable tension is applied. This is the regular pattern used on most Shimano mountains, all Shimano road, and all SRAM and Campagnolo derailleurs. In this condition, spring pressure takes care of the easier change to smaller sprockets. In road racing the swiftest gear changes are required on the sprints to the finish line, hence high-normal types, which allow a quick change to a higher gear, remain the preference.

Low normal rear derailleurs return the chain to the largest sprocket on the cassette when no cable tension is applied. While this was once a common design for rear derailleurs, it is relatively uncommon today. In mountain biking and off-road cycling, the most critical gear changes occur on uphill sections, where riders must cope with obstacles and difficult turns while pedalling under heavy load. This derailleur type provides an advantage over high normal derailleurs because gear changes to lower gears occur in the direction of the loaded spring, making these shifts easier during high-load pedalling.

Top normal derailleur
Picture of reverse pull drop derailleur

The internal derailleur is sealed within the shell of the hub gear, in contrast with derailleur gears where the gears and mechanism are exposed to the elements. 

Hub gear systems generally have a long and largely maintenance-free life though some are not suitable for high-stress use in competitions or hilly, off-road conditions. Many commuter or urban cycles such as European are now commonly fitted with 7-speed gear-hubs and 8-speed systems are becoming increasingly available.

Internal gear hub

3. The selection of the transmission system

Before choosing a transmission system, you must be clear about the usage scenario of the bike, and choose a complete kit according to the purpose. You can also choose compatible parts according to the actual situation and environment, after that assemble a mixed transmission system. However, this requires an in-depth understanding of the transmission system.

Transmission system kit

Thanks for watching. 

Don’t hesitate to leave a message regarding the transmission system if you have anything to share. We are looking forward to your idea and story.

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[1] ‘Cycling Bible’ Editorial Board. Cycling Bible [M]. 1st Edition. Beijing: Machinery Industry Press, 2013.

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