Just curious: why not ride a regular bike to work? I've been doing it for a year now (16.5 miles round trip) and it has been great. I never could find the time to exercise before and now I commute and exercise at the same time. Parallelism!
Because lazy! At least mostly. Also we don't have shower facilities at work, so during summer (I'm in Sydney, so summer hasn't quite ended yet) I end up quite sweaty riding to work.
I do have a non-cheater bike as well, I ride it more when it's cooler (but I'm still lazy, so...) More exercise is the plan. Executing on that plan isn't always successful.
I'm looking at getting a similar setup for myself this summer. I hear "that's cheating" or similar from others, in which case my response is: Do you ever use a calculator? Why not work out everything with pencil and paper (or better yet, in your head)?
Of course, several years ago after I decided to get in shape, I tried cycle commuting and really enjoyed it (about 15 miles each way). But I could only pull it off about once a week or so (in order to make good time, it left me mostly worthless at work all day). Coming up, after I move in a month I'll be about 23 miles from work. Adding a hub motor will allow me to not only make the commute in just over an hour, but it will leave me less exhausted (I plan on still putting in some human power, but I won't have to over do it). The good thing though, is by adding electric power to a bicycle, it will get me on it much more often so I'll end up getting even more exercise than without power.
I built an ebike last year to do something similar to OP. I rode my bike (a full suspension mountain bike) a couple times, but found that 20 miles was just too far to cover for a commute. With the ebike, I am still pedaling and getting exercise, but it takes me 50 minutes instead of 90. Still a tad longer than it would take in my car, but I am definitely getting a decent workout (determined by how sweaty I am before I shower). Even if I only burn half the calories, I am getting nearly 2 hours of exercise a day I wouldn't have gotten otherwise, and am not adding much time to my commute.
Maybe someday I will be in good enough shape to make the 20 mile commute in around 1:15 without the assistance, but if it's between pedal assist and driving, pedal assist seems like the far better choice!
FWIW, I used to bike-commute to school when it was 8-10 miles, and that was great. But 20mi each way is just too much time for me when I need to get home to get kids to practice, or help with homework, etc.
