I track my weight and body fat % everyday for my training log. I weigh myself first thing in the morning after using the bathroom. This allows me to stay consistant on weight tracking. I may also weigh myself after the training ride but I do not record this weight.

The problem with weighing yourself post ride is you would not be consistant as there are days you may not ride, and days you may ride harder or softer. Weighing yourself in the morning first thing will be the best bet. Weight increases would be from diet. If you ate something for dinner that caused you to retain water such as pasta you might see a gain in weight.

Because I am anal about this stuff I use an online software program and log what I eat, my weight, and time trained and calories burned each day. So if I see and increase in weight I can look over this program and will see a trend of increased calories. Same with a decrease in weight.