Why We Like The SIR 9 3-Star GX Eagle Mountain Bike
Steel is real—you’ve heard it for years, and we can confirm that the steel is worth savoring. The Niner Sir 9 Mountain Bike is one of the most versatile hardtails on the market thanks to its supple Reynolds 853 steel construction and a plethora of mounting points for bikepacking excursions. With modernized trail geometry, the SIR 9 is suited well for a daily driver on post-work singletrack jaunts, or for a dependable pack mule intended for multi-day long distance adventures. This 3-Star GX Eagle build boasts all of the bells and whistles we’d expect to find on the cutting edge dual suspension bikes, supplying an extremely capable platform at a fraction of the price of it’s squishy competitors.
Seeing that the bike industry is ever-evolving, it makes perfect sense that Niner designed the latest SIR 9 with their trail-country geometry, which makes the bike’s head-tube angle slacker and the seat tube angle steeper for the best of both worlds when it comes to climbing and descending. 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 tracks confidently when you open it up at higher speeds for added composure without it ever feeling twitchy or unnerving when pushed to the limit.
Paired with a 120-millimeter fork, you'll find 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 trail sections previously on the edge of the old bike's comfort zone. And though it's slacker than before, the SIR 9 still pedals and climbs with gusto, thanks in part to its steeper 74-degree seat tube angle, which places you in an optimal pedaling position.
Delving into the frame construction, you'll love the smooth, supple feel of SIR 9's Reynolds 853 steel, especially when you're rallying it over bumpy sections of rocks and diving into swooping corners where steel brings extra compliance to the terrain. 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 places a hidden inner-plate that stiffens and strengthens its integrity—all without compromising the steel frame's compliance and supple feel.
The modern Boost axle spacing increases frame stiffness to take some of the forces from impact away from the wheels, and boasts clearance for 27.5 x 3.0in tires. And because of its popularity in the bikepacking realm, the SIR 9 is loaded with a myriad of mounts for saddle bags, fenders, accessory carriers, and water bottles. You'll find 18 mounting points in total, with two inner-triangle mounts for water bottles, another pair of bottle mounts under the down tube, fender mounts conveniently situated on the rear stays, two bosses for a top tube bag, and another two bosses underneath the top tube for a bolt-on frame pack. In fact, there are so many mounts, we probably forgot to mention a few possible configurations, but we're sure you'll find a handy way to make use of them!
This particular build boasts top of the line 1x12 SRAM Eagle GX drivetrain components, with a mind-blowing 10-52t range which will be sure to tackle the steepest fire-road climbs. The Fox 34 Factory Fork perfectly balances cushy support for big impacts with a nuanced ground-hugging feel for traction through rock gardens and sweeping berms alike—all with 120mm of efficient travel. SRAM covers the stopping duties with their new trail-specific G2 brakes, paired with 180mm and 160mm rotors to ensure you are able to stop on a dime even on steep descents. Known for their reliability, DT Swiss M 1900 Spline Wheels are covered by Schwalbe’s Nobby Nic tires, with a cushy 2.6in in the front for traction on slickrock climbs and a 2.35in in the back for zippy rolling speeds on long rides.
- Steel-framed hardtail is suited for lunch rides or backcountry missions
- Slack cockpit and steep seat tube offer modernized trail geometry
- Fox Factory 34 fork supplies 120mm of rock-gobbling travel
- Eighteen mount points allow for infinite gear hauling possibilities
- Reynolds 853 steel frame is supple and virtually indestructible
- GX Eagle drivetrain supplies quick shifting and a wide gear range
- Schwalbe rubber supplies traction on slickrock and wet roots alike
- Race Face cockpit components offer a modern trail bike feel