My own opinion is the more you ride, the more carbs you need for the energy. I'm also not convinced that taking carbs out of one's diet is a particularly healthy way to go about losing weight, especially not in the long term.
i really agree with what chris said. i know people are seeing positive results from this diet, but what is happening is your body is going into citosis, which completely changes the way it burns food, turns it to energy, etc. the long term effect may not be as pleasant as the short term weight loss you might find. we do eat way too many refined carbs and starches in the western world, but the more you exercise, the more carbs you need. i would suggest changing which types of carbs you consume to include mostly whole grains, and high energy carbs... and riding as much as you can!!
by the way, i guess dr. atkins himself recently had a strange sort of heart attack, but won't admit that it had anything to do with his diet.