This is a logical fallacy unless you can control for the change in time of the number of riders, the distances they are riding, the type of riding they are doing, and the seriousness of the injuries. To take one potential example, the rise in helmet use over the last 20-30 years coincides with the increase in popularity of mountain biking. If you have statistics of serious head injuries/mile of road cycling (or insert another appropriate modifier instead of "road"), you should point us to them.