My commute is 30 miles round trip. I believe another 10 would be ok. I would be going easier at least on some days than I do now. I also weight train with my wife in the mornings. I might have to do less of that or more of it on weekends. I got home last night wishing I had further to go and it was raining the entire ride Therefore, I would definitely say that 40 miles round trip is doable.