Originally Posted by Chaco

Exactly the same thing happens to me. I weigh myself every morning. About 5 weeks ago I did a century. The next day, I was 2 pounds heaver. Yesterday, I rode 91 miles and burned about 3,000 calories. This morning, I was 3.1 pounds heavier!

My best guess is fluid retention. I drank 6 bottles of water during the ride and had about 40 ounces of water after the ride.