About the specifications of the BB shell of bicycles
Frame BB shell refers to the short pipe connecting the frame riser, the lower pipe and the rear fork. If the tooth tray is to be installed in the BB shell, it needs the middle shaft to connect. BB is the abbreviation of the center shaft (Bottom Bracket). The common BB shell specifications are as follows. The main results are as follows:
(1) BSA system
English gauge thread system BSA means that there are threads on both sides of the five channels, the left thread is the right thread, the clockwise thread is tight, the right side is the left thread, the counterclockwise thread is tight, the outer diameter of the thread is 34.798mm, the width of the five passes is 68mm or 73mm, the middle shaft of the middle shaft is BSA 1, 37 × 24. The middle shaft of square hole and the middle shaft of splines are more common on the low end mountain car, and the outer axle is more common in the highway car. The tooth disk crankshaft and tooth disk using the external middle shaft are integrated. The dental plates produced by shimano, sram and campagnolo all have their own matching middle shaft selection.
There is also a thread specification for gauge thread ITA, this thread is on both sides of the normal thread, the outer diameter of the thread 36mm, the shaft specification ITA 36 × 24. This BB shell frame is basically invisible now.
(2) BB30 bb30
was developed jointly by FSA and Cannondale. The bearing size of the middle shaft is increased by bb30 indentation shaft, the axial center of the tooth disk is thickened to 30mm (the diameter of the traditional integrated disk axis is 24mm), and the BB shell width is 68mm and the inner diameter is 42mm. To put it simply, Perlin (bearing) is pressed directly into the BB shell, the spring is placed in the BB shell to fix the bearing, and a gasket is added to seal the outside. However, this method requires very high caliber of the frame five links, even if the frame is qualified, a little attention may cause abnormal noise during installation.
(3) The BB86 and BB90 BB86/90
are substantially identical to the BB30 and are press-fitted, except that a housing is added to the outside of the bearing. BB86 and BB90 adopt a 24-mm diameter disc hub, the BB shell extension of the BB86 is 86.5 mm, the inner diameter is 41 mm, the BB90 BB shell is 90.5 mm, and the inner diameter is 37 mm.
BBright is an exclusive system introduced by cevelo. The diameter of the axis of the tray is 30 mm. Compared with the 68 mm five-way width of the BB30, the BBright is only widened by 11 mm on the left side of the BB shell side (the non-dental disk side), the BB shell width is 79 mm, and the inner diameter is 42 mm. That is, the BB shell of the BBright system is asymmetric. The following figure
has the requirement of reducing frame tolerance by adding composite bearing sleeve to the outside of bearing on the basis of BB30 because of the high precision requirement of bb30 system and the frequent occurrence of abnormal response in direct contact with the frame. The width of the BB shell is 68 mm, the inner diameter is increased to 46 mm, and the axial center of the disk is 30 mm.
(6) compared with BB30, the width of BB386 EVO increases to 86.5 mm, the inner diameter is 46 mm, and the axial center of disk is 30 mm. Under the condition of maintaining the thickness of disk axis, the width is increased and the strength is greatly improved. It is an ideal five-way design.