The streets are very flat here in SE Michigan, so I can't claim to mash, whatever that is. It does get windy, though, and I've had to stand to make headway. Most of my commuting has been on a Schwinn Suburban or Varsity, or a Peugeot P8, so I've never thought twice about standing up on them. Coming to a quick, controlled stop from 25 mph, yes, that's another story.