The SIR 9 is Niner's steel frame that allows the rider to choose from multiple set-ups with zero compromise. Single speed, 1x, 2x, suspended, rigid, whatever you want. You get 142mm rear spacing, an integrated post mount disc interface and the options to multiple bottom bracket adapters. The blend of premium Reynolds steel tubes, Niner geometry, and the speed and control of the 29er platform is inspiring to old school steel proponents who still enjoy the advances of modern technology. So what makes it so desirable? Well while steel has been the most successful and reliable frame material over the long history of bicycling, steel development hasn't stood still. Lightweight resilient tubes and shapes still offer the sensational ride quality, but are more responsive, with greater strength. Niner taps into the world of steel through Reynolds, perhaps the best known bicycle steel manufacturer of our lifetime.

The SIR features the legendary 853 blend, with Double Zone Butting, for the oversized downtube. DZB allows the builder to define localized shapes and strength that complement the tandem requirements of the downtube. You get the stiffness at the headtube and the bottom bracket you need, while the butting of the central zone delivers essential compliance. The top tube and seattube are also 853. Known for it's light weight, high strength and responsive, yet comfortable ride quality 853 has been a huge part of cycling history on the road, trail and track. For the now 44mm oversized headtube, Niner chose the 631 blend, which is heavier, but inherently stronger and holds large-miter interface welds perfectly. By opting for a pure 44mm headtube, Niner allows riders to choose tapered steerer or straight (even 1⅛ with a reducing headset). The short 631 cylinder will defeat torque and provide essential stability under any terrain or load.

The rear triangle employs s-bend stays and curves that not only transfer power, but offer compliance without ever feeling soft or squishy. When you put down the pedal power, the SIR 9 jumps to attention. Interestingly, Niner built the rear disc mount as a post mount within the triangle, which is common with carbon and aluminum, but not with steel. Investment cast drop-outs and bridges add strong connective junctions. The 12/142mm Maxle thru-axle system and rear triangle assembly delivers perfect wheel tracking and power transfer while accommodating most tires up to 2.4" width. Power comes through the oversized bottom bracket shell. Niner packages the frame with their 73mm wide BioCentric II bottom bracket, which allows for 8.5mm off center adjustment- or more than most eccentric options- for easy single-speed set-up and adjustment. Bio-Centric II requires external threaded BB models. Should you decide to run a 1x or 2x geared drivetrain, you just need to get buy the derailleur hanger and a Niner CYA adapter for whatever crank/BB interface you decide to run.

The geometry has been optimized for a 100mm fork, though an 80mm version will work just fine. Niner's dedication to 29er wheels has allowed them to constantly evaluate and improve their geometry and the SIR 9 loves it some XC trail action. The 440mm chainstays feel shorter and quicker, especially with the 70.3° headtube angle with a 100mm fork. Stable, quick, and responsive. Versatile, comfortable and affordable. Those qualities embody the SIR 9. We love it as a single-speed paired with a matching Niner rigid carbon fork, but the SIR 9 is any bike you want it to be. If you ride for the pure pleasure of it, and love to turn your bike loose, we highly recommend the ride quality of the SIR 9, which inspires confidence and delivers smiles on the trail.