Let's face it, somehow bike racers have a skewed vision of vanity. When was the last time a cyclist showed you his "great" tan lines? If you know many bike racers, it probably hasn't been long at all. But we all know that too much sun isn't good for you.
To help keep all the time in the sun in perspective, there's a great sunscreen info graphic on InformationIsBeautiful.net that has a very good description of sunscreen—what is protects against, how much to use, how long its protection lasts—and the types and dangers of skin cancer. It's definitely worth taking a look so you know what type of sunscreen to buy, how much to use, when to put it on, and what you're trying to avoid by using it ... least of which are those tan lines you worked so hard to get.