Hey, I'm coming back from a torn tendon and i need to get in shape for a 500 mile ride. We'll be averaging about 25 mph. I'm riding a Trek 7300FX(hybrid). Right now i can hold about 15-17 mph for 40 miles(thats the farthest i've ever ridden). I need to know what kind of training i need to do. The only grade on the trail that i know of is 13%.