Originally Posted by campfire

29" MTB and 28" road tires use the same rim diameter (622mm). Your 28" tires should fit just fine on that bike. If you got 28x2.00 (700x50 or 50-622), you probably won't even notice the 0.1" width difference compared to your existing 29x2.1 tires (though the way the tire rolls should feel quite a bit smoother). If you got a 28x1.50 (700x38 or 40-622), that's well within the range of common tire sizes for RAGBRAI. Either way, you would be fine.