I noticed sometime ago on MTBR that riders are swapping out their standard 26" wheels for 650B's (27.5 inchers), and that the Cannondale Prophet with the Lefty is great candidate for this conversion. What makes this a kewl fit is that the Lefty I have allows this bigger wheel with no modifications necessary. And the chainstays also allow for a bigger rear wheel, but the fit is little more snug. I prolly have 3/8" between the tire and the front derailleur, and about 1/4" gap between the tire sidewalls and the chainstays.
Why in the world would I do this??? 650B isn't widely used, but its popularity is starting to roll. The 29r (29" wheel)is already widely accepted tire convention, and using a bigger wheel chews up the bumps and roll really well. But in my opinion, those benefits come at a cost; bike geometry that doesn't fit the smaller rider, less sturdy wheels, longer wheelbase, and slower acceleration. The goal of this conversion is to capture some of the benefits of bigger wheels, while mitigating the weaknesses that hamper the larger wheel.
With these wheels the only geometry change is that my bottom bracket height/ stand over height increases about 3/4". The bottom bracket on my Prophet is already pretty low (XC mode: 13.7 & FR mode 13.0), so this isn't a big deal. Although the standover height for me is now a little higher than I'd like, but its not that bad. There is also a change in the amount of trail by using the bigger wheels, but I really don't notice it.
The setup I went with was silver Velocity Blunts (would've preferred black, but nobody had 'em in stock). The front hub is a Woodman Lefty, and the rear is Hadley 135mm Quick Release. The tires are Pacenti Neo Moto's, which I'll convert to ghetto tubeless in the near future. Since this isn't that popular of a wheel size, the tire selection is pretty small, but I actually love these tires. They roll fast, here in the desert. Availability is also a problem, because I doubt there is a shop in AZ stocking this tire, so I ordered a third tire. That way I'll have a spare handy, in case I have a sidewall tear.
So far the wheels feel far stronger than the cheap wheelset I've been rolling on, despite the larger less rigid wheel. And I tried to mitigate the slower acceleration by going with a faster engaging, high quality Hadley hub. And since the only geometric change is for my ride is a higher standover height, I don't feel hampered by it.
I love the new feel of my bike. It chews up the bumps, which allows me to keep rolling in crucial spots of a technical trail. I do sit up a little higher, so I haven't found the point where I can rail. And if I roll on some super hard trail that demands a smaller wheel, I can easily swap out 'em out for my old set.
I purchased the rims and hubs from Universal Cycles. I got a good deal on the tires from Speedgoat. And Mike from Curbside Cyclery built the wheels.
To learn more about 650B, here are a couple of sites:
sixfiftyB and 650B Palace.
Here's short vid of what my bike looks like with the new dubs: