"We notice in bikes that are well-thought out that the differences in geometry and design would seem to amount to very little---half a degree here, one centimeter there---it doesn't seem like much.  This is what I call the rule of two percent (R2% hereafter).  That is, everything is more or less the same till you get to the last 2% and in that makes all the difference.  So what difference does this difference make?  In wheel diameters it's downright amazing.

The difference between a 559mm "mountain" bike wheel and the 584mm 650B is amazing.  (Hmmm, is this 2%?  I never did the math...but it's the principle, not the math! Anyways...)  The key is "roll": the sense of momentum that a bike carries when you stop pedalling.  The problem with mtn bike wheels, as I see it, is that you stop pedalling and the bike just seems to die.  This would be a good thing on technical trails and the like because you don't want the thing running away from you.  But on dirt roads, non-technical stuff, or when a sturdier sized wheel seems like a good idea (be it weight-bearing for panniers or just lower center of gravity), then 650B steps in to make the difference.  The 650B rolls like a 700c road bike wheel but gives you that far more fastened-to-the-road feel of a mountain bike or commuter wheel.   This is undoubtedly the best of both worlds and with a skinner 32c tire the roll puts you at no disadvantage to a road bike; with the fatter tires, well, you can go just about anywhere, including the most technical stuff (depending on your skills which are always the issue)."

"...my converted 650B bikes are just fantastic with these wheels, and I don't ever see a time when I'll return them to their 700C configurations, or change to another wheel size."

"The bike retains the agility and road manners of it's original design, and adds a level of stability beyond that which is evident when fitted with 700C wheels. On pavement, the bike turns direction easily and holds a line well in corners. The large 650x38B tires handle a variety of surfaces; broken pavement, rippled and rutted pavement, and even cobblestones. While it is obvious that there is a large tire beneath the rider, the bike does not feel sluggish.

On dirt, the bike feels fast and stable enough to ride at speed. It is capable of limited single track, and twisting descent on dirt roads within the limits of adhesion of the tread of the tires. Small ripples in hard pack surface are muted to the point of insignificance, and the bike rolls pleasantly over undulations and wavy surfaces."

"I rode on the cobblestones in the Old Port area of Portland. These things are punishing, I have nothing but respect for those who ride the Paris Roubaix. The 650x38B wheels were the smoothest yet here, and if I'd dropped the pressure to 35-40psi, I could have gone even faster and in greater comfort.

I covered some singletrack on the shoreline around Portland's Eastern Prom. No sweat, even on a few feet of slick rock with a 45 degree drop. I heeled around and went back around Back Cove to the North side.

I  pedalled along Falmouth Foreside on Route 1, and through the WalMart Plaza. I rode past the Town Library. At the top of the hill I turned right to see that the traffic light at the next intersection was going to be turning green for me momentarily; I made the shift to the big ring, jumped on it, and flew through the green light. The bike felt plenty fast."

"In any discussion that you are likely to have with anyone who has either experienced 650B, or fully understands the implications purely from a theoretical point of view, the only downside is availability. That's it: availability. Make them available to people, and everyone breaths a deep sigh of relief and makes plans to go about building or designing bikes around them."

I can't imagine a build further in spirit from its original full Campagnolo Super Record incarnation - but these conversions have a certain swords-into-plowshares quality.