There is always a strange noise in the middle axis of a mountain bike-it is the culprit!

I can't believe it! The central shaft is the rotating part installed in the five links of the frame to connect the left and right crank. General sports cars are common square holes, splines and integrated three kinds.


Shaft in square hole is the most common because both ends are square, so it is easy to identify.

It is improved on the basis of the traditional pin center shaft. The pin type central shaft is locked by a single pin, which is easy to be damaged due to the small contact surface. It is now only available in relatively old-fashioned civilian vehicles. The performance improvement of the shaft in the square hole lies in increasing one contact surface to 4, the force is more uniform, the strength is higher, the force conduction is better, so the market is dominated for a long time. Each manufacturer has the model of the shaft in the square hole.


Spline shaft has just been launched a few years ago, each manufacturer has introduced the concept of integrated shaft, and in its high-end series production. 

The so-called integration is to separate the axis of the shaft from the bearing and combine it directly with the crank on one side, and the position of the bearing is moved from the five-way inside to both sides. The advantage of this system is that it reduces the number of parts, reduces the weight and improves the structural rigidity, the distance between bearings is larger, the burden of bearings is reduced, and the strength is improved. In fact, this technology has been widely used in BMX for a long time, which is not unusual.