I commute in Seattle on an old road bike with fenders, lights, etc… I don’t worry if it gets covered in road grime or rain or picks up a few scratches from the bike rack. It is still a good bike though, and well maintained, so I do enjoy riding it. In Chicago I commuted on an MTB with slicks because the roads were so crappy and laden with debris that the larger tires were more durable.
I think that it is nice to have a dedicated commuter set up properly. That way you don’t have to worry about your nice road bike getting banged up and you don’t have to remove the commuter accessories from your regular bike for training/racing.
CCX is about the best commuter around if you have hills. Fixie with clearance for fenders is pretty good too. Go used, if you keep your eyes open, you might be able to get both for $1k.
Call the local police department (or local college - good place), ask when their auction is, and buy a decent commuter for nothing. Upgrade a few items like gearing (if necessary), or convert to SS; then add paniers and GOOD lights; some commuting clothes; and finally your saddle of choice…this is <$1000 budget and covers all necessary items, rather than spending $950 on new bike, then having to buy plenty of necessary extras.
Problem with commuters is potential for theft, so cheap is often good, with detachable premium items.
If your routes aren’t too hilly, fixed gear or single speed is a great way to go. Slap on fenders and you can ride in pretty well any weather. Chains and cogs are cheap and durable and it’s cheaper than dealing with cassettes, derailleurs and multi speed chains. There are several reasonable FG/SS bikes out there now for a lot less than $1,000. If you need gears, an old (or new but cheap) cross bike is a good choice.
I really like my Surly long haul trucker frame, fender mounting is easy, the geometry is comfortable and you can run big fat tires, it’s very affordable and rides great http://i5.photobucket.com/albums/y173/jroden99/sur003.jpg
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Fixed all the way,
Daily maintenance is nothing.
Fun to ride.
You can practice balancing at red lights, so you never have to come out of your pedals.
You get all those added miles on a fixed, rather than typical road/tri/mtb miles (nice variety).