Steel is real.
The Niner SIR 9 29 2-Star SLX Complete Mountain Bike is one of the most versatile hardtails on the market with its supple Reynolds 853 steel construction paired with modernized trail geometry, 29-inch wheels for steam-rolling capabilities, and 18 mounting points for bikepacking adventures. Whether you're seeking a steel hardtail for spirited rides through the local mountains or a dependable pack mule for long-distance adventures, the SIR 9 satisfies your itch for exploration with its simplicity, strength, and unmatched versatility. The customization doesn't stop there, with the SIR 9 swapping the momentum-carrying, obstacle-rolling 29er wheels for the voluminous traction and bump-smoothing ride of 27.5+ wheels. This is a great feature, as you can swap wheel sizes at a moment's notice to accommodate different trails and riding disciplines.
Since the bike industry is constantly evolving, it makes perfect sense that Niner designed the latest SIR 9 with their [R]evolution trail geometry, which makes the bike longer in the top tube and shorter in the chainstays. This redesign gives the SIR 9 a lively personality that's quick to turn through tight switchbacks and sweeping berms, as well as making it roomier in the cockpit, so you're well-balanced and comfortable across long distances. The longer wheelbase inspires confidence when you open it up at higher speeds without it ever feeling twitchy or unnerving when pushed to the limit.
Paired with the provided Reba RL Solo Air fork with 120-millimeters of travel, the SIR 9 moves from a rather XC-focused head tube angle of 70 degrees (for the previous model) to a more trail-worthy 68 degrees. This gives you added confidence to attack fast descents and technical sections previously on the edge of the old bike's comfort zone. Although it's slacker than ever, the SIR 9 still pedals and climbs with resounding efficiency, as Niner designed it with a seat tube angle of 74-degrees, which places you in an optimal position for laying power to the pedals.
Seeing that its name is derived from the catchy phrase "Steel is Real," it only makes sense the SIR 9 retains its beloved steel construction for a smooth, compliant ride over jarring sections of trail. However, any old steel wouldn't satisfy the discerning riders at Niner, leading them to use Reynolds 853 steel for its supple characteristics and high levels of strength. Reynolds 853 steel is heat treated and air hardened, meaning the weld zones actually increase in strength after cooling, making them impressively resilient to the regular stresses of trail riding. Inside the frame, Niner placed a hidden inner-plate that stiffens and strengthens the frame's integrity—all without compromising the steel frame's compliance and supple feel.
This particular 29er 2-star build delivers the no-nonsense shifting and wide range of usable gears of a Shimano SLX 1x11 drivetrain. The 11 to 42-tooth cassette provides ample low-end for grinding up the longest climbs without compromising power output when you're cranking away across flats and pushing downhill at high speeds. Shimano SLX disc brakes offer dependable stopping in the nastiest trail conditions, with a larger 180-millimeter front rotor for a bit more force where it's needed most. The build is rounded out with a Niner alloy wheelset with Boost hub spacing, which creates a stiffer, better tracking wheel when you're rallying across the rough stuff. There's also a KS LEV SI dropper post for on-the-fly changes in saddle height, with internal routing keeping the bike looking clean.
- Niner's most versatile hardtail in steel for supple feel
- Reynolds 853 steel adds compliance for smoother ride quality
- 29er version provides greater speed and obstacle rollover
- Modern geometry for lively handling and long-distance comfort
- Boost spacing accepts both 29 x 2.5 and 27.5 x 3-inch tires
- 18 total mounts enhance carrying capacity for bikepacking
- Shimano SLX 1x11 drivetrain with 42t cog for steep climbs
- RockShox Reba RL fork with 120mm of bump-smoothing travel
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SIR 9 size by rider height
|120mm Travel Fork|
Effective Top Tube
Head Tube Angle
Seat Tube Angle
Bottom Bracket Drop