The chain and gear sprockets are progressively getting thinner in pursuit of lower overall bike weight. This is driven by the racing side of cycling, similar t

The chain and gear sprockets are progressively getting thinner in pursuit of lower overall bike weight. This is driven by the racing side of cycling, similar to automotive tech coming through R&D in Formula 1 racing. A lighter bike is nicer to ride. It is less effort to accelerate from a stop and a 1kg difference will be noticeable when riding up hill. The trade-off of the thinner drive train components is that they will wear and stretch faster. Continuing to use a stretched chain will cause accelerated wear on the sprockets. When the sprockets get too worn the teeth become very pointy and chain will start to skip on the rear cassette or drop off the chain rings. Track bikes (fixed gear, single speeds) are the exception, as the chains are still very thick as they are designed to take more force from acceleration from the track sprinters.