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Today's fold-up bikes grip solid ground

Today's fold-up bikes grip solid ground

The folding bike is riding the cycling commuter wave, and the clever engineering is making it quicker than ever to carry on a subway or in a car trunk. Now found in some regular bike shops as well as specialty urban-transportation stores, better designs are helping the bikes shrug off a nerdy-professor stereotype of being ugly, tiny-wheeled, poor-riding machines. Breakthrough models come with chainless belt drives, electric engines and even recumbent formats. Most sport 20-inch wheels to make the bikes compact when folded, with elegant frames that hinge and lock at mid-frame. That keeps the drive-train area (front chain rings to rear wheel) intact and makes the bikes so solid that you almost...