I can comfortably ride 15-25 miles, four times a week (usually 18-20). I started riding about 9 months ago and 12 miles felt long then. I agree that the difficulty of the ride determines the distance (mostly hills). About 2 hours is a good amount of time for me.

I like knowing how many miles I have gone using my bike computer. I was completely jazzed when I passed 1000 miles total. I'm still not fast enough for most club rides, but I have met a cycling buddy. I like better to ride with someone than alone. You have back-up if you are out on country roads, and someone to talk to during a break.

But yesterday, I did a stretch ride in this absolutely fantastic weather we have been having in central CA. It's been 70 degrees and sunny! Can't hardly stay in the house. We went from north of Monterrey to Carmel and back. What I did not know was that there was a giant mountain we had to climb to do this coastal ride. It was 35 miles and not easy. I got home and was completely exhausted. I think I'll wait awhile before I tackle this climb again, but it was nice to be able to do it.