The new 180 240 or other use with dt exp structure, the old 240 cannot be used (note that some , such as , etc., use this structure, make by yourself) This model is EXP unilateral drive version/54T Advantages of 54t . First: Less trampling dead spots, easy to start climbing Second: When you to accelerate downhill or rush out of the team, it is much easier than 18t to exert force, and there is no need to change gears in advance Third: The sound is much 18t (The front chainring is 32t and the rear flywheel is 32t. The gear position is, Take the 18-ring dt hub as an example, There are 18 teeth in a circle, which means that the distance between each tooth is 20. That is, there is an idling angle of 20 when starting; If the front chainring is 24t and the rear flywheel is 36t, when you are afraid of steep slopes, There is an idling angle of 30 degrees, and the pedaling dead point is very . It's hard to started. If it is 54t, because the number of teeth is three that of 18t, Therefore, the tramp dead point is only one-third, and it is easy to start climbing steep slopes. It's more obvious when going downhill, if you to accelerate suddenly, The 18-ring hub, the legs have to be trampled crazily, In order to allow the hub ratchet to quickly bite into force later, and the 54t hub is much easier) Approximate diameter of ratchet wheel: small ratchet wheel 27.6MM, ratchet wheel about 29.8MM Material:Aluminum alloy colour:Silver + Red Package Contents: 1 x Ratchet remover Exp tool Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.