I cycle about 23-27 hours a week and wear glasses as not only protection against the sun, but protection from objects such as bugs, etc.  I have utilized Oakley Radar sunglasses for a considerable amount of time, but they fail me in one of my needed missions.  I'm an avid time trial competitor and when I compete on my time trial bike, I utilize a Kask helmet with a pull-down visor, hence I do not need sunglasses when I am racing.  When I am training on my time trial bike, however, I always find myself looking at the top rim of the Oakleys when in the aggressive TT position on my aerobars.  The Smith Pivlock glasses are perfect for that mission.  I now have an unobstructed, very comfortable view of the road when riding in that aggressive, flat back position.

The lens can be changed in seconds between the 3 sets of supplied lenses, and the glasses and spare lenses/extra nose piece come in a nice, solid, large, very protective, zippered case.  If I have one criticism about the glasses, it would be that in the hot, humid weather of the Florida summer, I seem to sweat under these glasses - something that I do not do with my Oakleys.  Perhaps it is just a function of my face geometry.

The glasses are incredibly light (1 oz on my postal scale) hence very comfortable to wear.  These are probably the best sport glasses out there, and at about half the price of the Oakleys, you cannot go wrong.  Also, after searching the web, I found the best price to be right here on Amazon.