At customers’ requests, Siren Cycles has added a swooping Constant Radius Top Tube as an option on their John Henry hardtail 29er mountain bike.

The steel bikes are available as totally custom options, as these two bikes illustrate.  The matte black one on top has extra curvy chainstays (better illustrated on Siren’s blog), while the sparkle-over-cream off white bike after the break gets beefed up chainstays for the XL frame…and they paint matched a rigid fork and Reba lowers.

The new CRTT required special tooling and new dies, plus a lot of forearm work, and now that they have the equipment, they can make one just for you, too.

What do you think?