My commute is 22 miles round trip, 10 going to work and 12 riding home a longer way, riding 3-4 days/week. In a year or so, my office is moving downtown, so my commute distance will increase to about 15 miles each way. That is very doable in my book. However, it would be difficult for me to jump up to say, 20 miles each way, just because of the time involved. Right now, my commuting takes about 1-1/2 hours each day, and it will take about 2 hours each day when it jumps to 30 miles RT. Commuting 40 miles/day would take me about 3 hours, and I wouldn't want to commit that much time riding 3-4 days a week. However, I would probably still try to ride 2 days/week if I had a longer commute distance.