This is very surprising. The Coda is not a heavy bike. Check tire pressure as suggested, and for rubbing brake pads.
When you did the ride on your road bike, did you actually do the commute during the week (with traffic, etc.) or on a weekend with no traffic? Are you in the same strong shape now as you were last spring? My overall speed on commutes is lower than when I'm riding my road bike on back country roads. There are lights and traffic and all sorts of urban happenings on the commute.
I don't know how urban your commute is, but I had a commute of the same distance as you for five years through Washington, DC. When I first started, I was slow, then I got stronger and faster, then I got a new bike (the Coda--upgraded from 1980s mountain bike) and got faster still. I got it down to about 1 hour 10 minutes, which doesn't look good on the computer but I can't synchro the traffic lights. There's only so much speed to be gained on an urban commute. It was still faster than the Metro, and often faster than the car (when I take into account the 4 times a day I had to move the car to avoid getting a parking ticket).




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