Love commuting on my current steel monstercross (Origin8 CX700) buildup but...

One of my all time favs is still my old mid 90's steel trek mountain bike w/ upgraded everything including Long Haul Trucker forks running Big Apples, racked, of course. Super smooth, simple, durable, versatile, and fun. Allows me to take routes not possible on roadier setups and not that much slower on the city streets, anyway. Estimated 25-30K miles on this old steel frame, much of it pulling a trailer/trailabike w/ one or two of my 4 kiddos. Quite a good bit of it off pavement. My mtn bike is still a wonderful commuter setup for me in the conditions here in austin, tx.

Keys to this type of setup are steel frame and forks, wide smooth rolling tires w/ flat protection, good fitting saddle, and racks.
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my two cents...