My GPS said it was 20 miles, but while actually doing it it told me it was only 19 miles. I managed to keep up a 15mph average. The last two hills knocked me down from 15.4 down to 15
To put this in perspective, At Mid-June when I started riding(vision R-40 recumbent SWB) My first 3 miles I did wiped me out and I hit about 8mph average. Then a month later I did the last 5 of the 20 I just did, and I managed 14mph, but the two hills at the end, even when switching to lowest gear, beat the crap out of me.
Now though, I did the full 20 miles, and the last two hills were a breeze(went up them in my starting gear on the recumbent), not to mention I think I could of done another 10 miles pretty easily. Next goal is a 30 miles, perhaps a full round trip(38 miles) if I can do it.
I am kind of beat today though(but not very sore, which is cool), so I am relaxing, probably will try the 30 this weekend, as I don't trust the weekday commuters-in-a-death-machine-I-swear-I-didn't-see-that-bike type of people.
For those of you that may just be starting, keep it up, it gets better very quickly once you can start doing 5+ miles at a time, at least for me it did.