I have 20's on my road bike and 25's on my fixie. I have a few RR tracks to roll over on my commute so 25's help. I would recomend a fatter tire on the rear because you can lift your front wheel easier than your rear (at least this is the case for me)
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I'm not one for fawning over bicycles, but I do believe that our bikes communicate with us, and what this bike is saying is, "You're an idiot." BikeSnobNYC