I wouldn't say I am maniac for cycling, particularly when some lunatics make 100km trips per day. For me 10 km has been ok, 20 km quite a lot since when I'm on the bike, I work hard and go more or less at maximum speed. With 10-20km trips I've still been able to collect 550km for this season that started in May and ends somewhat in September.
One limiter has been my capacity to bear the saddle. It is nasty, up until now the 20km has felt a lot, even if I'd have energy and stamina to continue, legs saying "let's continue" while the pants say "I wanna go home". Up until now, since I bought cycling pants with the soft part enabling me to extend the trips. Yesterday I did 28km and was ok to continue...
So if your ass limits you from making longer cycling trips, go to the shop!