Randy’s 650b Race Machine

Randy in Wisconsin commisioned us to build his 650b dream machine.
This Song SL is quite the race machine, perfect for midwestern singletrack.

We haven’t worked much with 650b (aka the ‘tweener size) as I’ve been pretty happy with 29″ wheels myself. Randy sold me on the merits of the 27.5″ wheel platform, namely the lower rotational weight (quick acceleration- key in the midwest), and more design real estate to work with on my end.

Randy called for the PressFit 30 bottom bracket platform, something we’d been hearing a lot about from our Srammie friends. We started the design work around the 156mm Q factor XX crankset, with good clearances around the Song’s titanium flex plate. After some trial and error, we arrived at a good process for machining & post-weld reaming the shell. By design, the system is very simple. As of now reaming tools aren’t available for this system yet, so we had to fixture the frame and ream it with a boring head on the mill. Not the easiest work but thankfully not something that bike shops should have to do.
This bike has a one-off shell that I machined by hand; future PF30 bikes we have in the queue will hopefully use a CNC’d part.

Randy also called for a Cannondale Lefty fork, which can play nicely with his chosen wheel size. We designed the axle/crown height of the bike to split the difference between the aforementioned fork and a Reba XX 29 fork, in case he were to ever want to switch. Rather than build the bike around a one point five head tube, we used a standard 1-1/8″ size, made possible with Randy’s use of the Project 321 steerer tube.

The frame: We built the bike with Easton Scandium, down tube and seat tube, and an Easton Elite top tube. The rear triangle features our proprietary Song goodies, and raw titanium seatstays for enhanced durability and suspension action. We went wtih a Smoke, White, and Red color scheme complimentary to both the SRAM XX group and the Lefty fork.

The custom wheelset was provided by our friends at NoTubes. They built the 355 hoops around a DT240 rear hub and a Project 321 Lefty front hub. Randy finished the wheels off with a pair of Pacenti Tires.

The bike was assembled by Fon Du Lac Cyclery.
The finished product weighs about 22.75 lbs with “all season” tires. Randy believes the race weight will be lower. I can’t wait to see this thing at the races!
The complete build list:

Frame: Siren Song SL 650b
Fork: Lefty Speed Carbon SL DLR with Project 321 Steer tube
Headset: Chris King
Stem: Syntace F99
Bars: Truvativ World Cup Carbon
Grips: Ergon
Brakes: Sram XX
Shifters: Sram XX
Cranks: Sram XX BB30 with PressFit 30 Bottom Bracket
Front and Rear Der.’s: Sram XX
Cassette: Sram XX
Pedals: Time Atac
Seat Post: Syntace P6 Carbon
Seat Post Clamp: Salsa
Seat: Bontrager inForm RL
Front Wheel: Stan’s ZTR, DT Rev Spokes, Project 321 Lefty Hub
Rear Wheel: Stan’s ZTR, DT Rev Spokes, DT 240 Hub
Tires: Pacenti Neo-Moto trail tires, Pacenti Quasi-Moto race tires.