There's a long but gradual downgrade on my ride home and I've clocked myself at 26 MPH before my chainring maxes out (I have a mtb crankset). The fastest I've ever taken the ole clunker was 45 MPH on a weekend century ride where I coasted down a very loooooong but steep closed road. But since that wasn't part of a commute I can't count that in the poll My average speed on the flats is probably 17-19 MPH. There's about a one-mile section of my ride that goes through some marshland (they built a smooth concrete bridge/roadway over the marsh) and I get a pretty good tailwind so I always feel like a champ on that part. Woooo!