The reason why we all loved our bicycles when we were little, and the professional riders as well who are athletes and still love to cycle their way to the furthest of destinations (some people do in Japan and China as well as in US); they all love it because the simple machine constitutes a lot of exercise and workout for it to function. Some bicycles that are used by the elders and the professionals also have a Gearing Component installed along with the chains that allow the users to transfer much lesser strain to their legs while pulling their bikes over at various diagonal paths. The bearing suppliers that are preferred by the professional bike producers are always those who rely on quality and consistency of the parts.
The bearings and the plates, the gears and the chains; are the major portions of the bike and each and every part of it is important without which the whole machine (your bicycle) becomes unusable. The gears allow the users to enjoy better performance by unloading much lesser pressure on the body and the chain attached with the pedals as well. Generally the starting inertia of the ride is the most difficult of all; once the ride comes at a particular speed, then it gets much easier for the rider to cycle it onwards. The gears allow him/her to stay at ease while the very first gear is designed for MORE cycling with the legs, and less functioning with chain speed. It is all a mechanical expertise.