Posted by: Brendan | July 13, 2011

Siren goes full squish… 650b FS Special Project

A Special Project bike for Mary in Washington.. the first of a new generation


Mary in Washington is a repeat Siren customer; she wanted something squishy to complement her Fifty-Five hardtail. I had talked with the folks at Ventana Mountain Bikes about working with their suspension system before, and was waiting for the right opportunity to use it. After some discussion, we decided the time was right to build up a full suspension Siren for Mary… next we needed to settle on the design.

We talked first about building another mixed wheel platform bike, but decided we wanted to go “big” for even more roll-ability. We considered 29″ wheels but decided they’d be a touch unwieldy given Mary’s small stature. We settled on the 650b ‘tweener size. While parts can be hard to come by for 650B stuff, we all noticed that the wheel size doesn’t seem to be going away, either.. so we jumped in.

We considered aluminum, steel, and titanium for the front triangle construction. We agreed on aluminum for the best material choice, given its light weight & stiffness, both very good traits to have in a full suspension design.

Ventana offered the rear suspension with rocker links to accommodate for 4″ or 5″ travel settings. We went for the shorter travel in the interest of a relatively lower bottom bracket and improved standover clearance. We also used a Fox RP23 damper, factory tuned for the job.

We designed the bike around an X-fusion fork with 120mm adjustable travel. We mimicked the confidence inspiring fit & geometry of Mary’s custom Fifty-Five, and prepped the bike for the classy green powdercoat job.

The Ventana rear suspension setup was easy to work with. I had to manually machine a few interface parts, including the pierced seat tube barbell for the rocker link, and the main pivot assembly. I fabbed up a large gusset into which the main pivot lives, with an internal rib structure for extra rigidity.

I suspect we’ll have more bikes like this in the queue before too long, given the bike’s performance & value. (priced in the neighborhood with other high end USA made FS bikes) This relationship with Ventana allows us to offer a proven, supported suspension system and couple it with our own custom fit, geometry, style, and handcraft.


  1. Looks AWESOME! Has anyone looked into a 29’r front with a 650b rear set-up?

  2. Thanks Vince. That setup would be totally do-able for us. Coincidentally, I have a hardtail in the queue going that way.

  3. Is that ISCG05 I see? I’ll never run a squishy bike again without a bash ring and two ring chain guide such as the LRP. Nice looking bike!

  4. Scott The Cop- your eyes don’t deceive you, good sir! She doesn’t have immediate plans to put it to use but we figured it couldn’t hurt.

  5. Hey! I like that color! 🙂

  6. Funny, I was just thinking about ” * ” the other day.

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