Originally Posted by
meanwhile
The weight difference that counts is that of the rider plus the bike; save 5lbs on the bike and you've still lost only, say, 5% of real weight. This might make you accelerate 5% slower or climb a hill 5% slower (unless the hill is a steep one, in which case the MTB gear might give better performance). But really, you won't notice.
As for wheel size, most of the people who prate about the subject have no understanding of the basic physics or practical physics. There are pluses and minuses of 26 and 700 size, the most noticeable being that a slicked 26 is easier to turn at typical traffic jamming speeds - 20s are much better again. Tyre resistance is highly complex; the bottom line is that 26s used to lack really good road tyres but they don't any more. Conti Sports Contacts are excellent. Oh - and 20 and 17 inch Moultons are banned from road racing by the UCI as unfair competition.
Say what you will, but I can easily ride my road bike 30% farther than my slick-tired mountain bike at an average speed that's about 20% higher. Bicycle maneuverability, in my experience, has very little to do with tire size. Rake, trail, and the amount of leverage you're able to exert through the handlebars seem to have more influence than wheel size or weight. In any event, both my road bike and my slick-tired MTB turn quickly enough to avoid almost any obstacle. Then again, so does my 400lb motorcycle at 60mph...