1. Thickened wheel with quality PU material: We were looking for quiet and durable bicycle wheels, especially those that can also play a role in shock absorption. This drive wheel made of quality PU material fits with this bill. Meanwhile, a thicker wheel with a thickness of 2.5 cm (0.5 cm thicker than an ordinary wheel) can reduce bumps and allow easy riding with less effort and more comfort. 2. Universal diameter and size available Still hindered by the fact that some bicycle drive wheels can only fit one or two bike sizes? This is the solution. Our training wheels with a fixed bracket featuring 5 different holes can meet your needs to mount it on bicycles of sizes 12, 14, 16, 18, and 20 inches. Its round silhouette and beautiful look fit together. (Note: Not compatible with variablespeed bikes.) 3. Double Bearings and Larger Washer After optimization, the double carbon steel ball bearing of the drive wheel has been tested to be quiet and smooth, with a longer service life. In addition, we have specially enlarged the washer so that it can cover the entire bearing well. This ensures a stable ride even after prolonged use.