[JAGG]

Here is my problem with riding my bike. I am a runner and I run almost everyday. I have never had this problem when I run. But when I ride my bike, I set out on a course I map for myself , for example 7 miles then turn around come back. But what happens is I can never gauge what is a good distance for me that day. I always end up going out and I feel good then I turn around and seems like I lose my energy and it's like a biking marathon to get home. Or I do the opposite , I am almost home but I feel like I can go for 10 more miles. Anyone else have this problem? Any suggestions. It's so much easier to know how far I want to run on any given day, the second I put my running shoes on I make that decision.