In mid-September, I'll be starting a two-day per week commute of approx. 21 miles one way. It is all paved bike trail, except for roughly the last mile, which will be downtone streets. I'll be commuting on Monday and Wednesday.

This seems almost the outer limits of what is practical. If the one way mileage was 25, I don't know if I would have considered it. Or, if I needed to commute more than two days, this may have caused me to question whether it was going to work.

A one way of 40 miles seems excessive and impractical for one to maintain for any length of time. I agree with the other postings about trying to break up the ride in half.

Best of luck and I hope you find a way to make it work.