Friday, January 11, 2013


All I have to say to preface this mediocre photo (taken before I installed the shock mounting points and cable stops) and geometry info is this: if you're going to do a 650b frame, take advantage of the wheel size. I see bikes like this or this or even this and say to myself "I could build that exact same geometry with 29" wheels". The chainstays and wheelbases are quite long, and there's really not much else to distinguish them from an equivalent 29" wheel setup in my mind.

Around here, we pull out all the stops. No 45cm chainstay monsters for me. If you're going to build your smallest frame with a 44" wheelbase... you should just give up and do it as a 29er, because the bike is going to be a total tank no matter how small you make the wheels.

Without further ado:

-4" of suspension travel front and rear.
-70 degree HTA and 72 degree (effective) STA.
-57cm/22.4" effective toptube and 62.1cm front center
-17.5" seat tube (center to top) with a very sloped/braced toptube.
-42cm chainstays, 104cm/41" wheelbase.
-33.5cm/13.2" (unsprung) BB height
-About 6.5# with an RP23 bolted on. Could whack off some of that (150g, maybe) if we had ditched the super low toptube/brace but Lee wanted plenty of standover (standover is 28").

In short, this is an all-around XC rig for the mountains around Boulder, which should be reasonably stable but also capable of being thrown around corners and bunnyhopped over logs down Todd Gulch. Lee won't fit on 29" wheels but we can get him some of the extra rollover ability this way without giving up... well, much of anything.

The bike will be a King/Enve/Easton/XX1 bling machine. Wouldn't be surprised to have the weight come in under 22# complete.


Anonymous said...

Very Nice - Ventana rear end on it?

Walt said...

Yep, good old Ventana single pivot.

Colin said...

It appears that the links to the first two examples of ill-constructed 650B bikes are the same. I'm curious what the third example is, both Rocky Mountain and Norco's 650Bs seem to have reasonably short chain stays. Maybe it's not one of the larger companies.

Walt said...

Fixed that, thanks. The link was supposed to be to Jamis. The RM and Norco (different chainstay lengths for different sizes! Awesome!) are decent, for sure, but I'm guessing <500 of those will ever exist. The "mainstream" 650b stuff is all godawful long.

steve garro said...

For sure - when I build 650's I use angles & CS lengths for 26'ers.
Tight, right & outta sight!
Sharp bike, Walt!