Item # NNR0069
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Niner SIR 9 Mountain Bike Frame - 2018 $1,200.00
Savor the steel.
Reincarnated for 2018, the Niner SIR 9 Mountain Bike Frame is one of the most versatile hardtails on the market thanks to its supple Reynolds 853 steel construction paired with modernized trail geometry, the ability to run 29-inch or 27.5+ wheels, and 18 mounting points for bikepacking adventures. Whether you're seeking a steel hardtail for spirited rides through the local forest or you're looking for 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 accommodating both geared and singlespeed drivetrains, although singlespeeds require Niner's Biocentric 30 (not included).
Seeing that the bike industry is ever-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 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 recommended 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.
Looking at wheel size compatibility, the SIR 9's Boost axle spacing clears both 27.5 x 3.0 and 29 x 2.5-inch tires. This means you can run it as a speed-carrying 29er with obvious roll-over advantages or with monstrous 27.5+ wheels that smooth out rugged surfaces and grab onto loose dirt with voluminous traction. Another benefit, Boost spacing stiffens up the rear wheel, meaning you'll reap the benefits of more precision when you're tracking across the rough stuff.
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!
- Niner's most versatile hardtail in steel for a supple feel
- Reynolds 853 steel adds compliance for a smooth ride quality
- 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
- Compatible with 1x/2x/3x drivetrain or singlespeed (consult specs)
- 73m PF 30 bottom bracket shell (bottom bracket not included)
More SIR 9 builds
View more Hardtail
|120mm Travel Fork|
Effective Top Tube
Head Tube Angle
Seat Tube Angle
Bottom Bracket Drop
Reviews & Community
Heavy Metal Trail Hardtail
- Familiarity: I've put it through the wringer
I am 5'11" and have a 32" inseam. I went with a size large frame and it fits great. I built mine up from the frame up (Deity cockpit, Ergon saddle & grips, PNW Components Bachelor Dropper, Rockshox Pike 130mm, GX Eagle drivetrain, and Guide RSC brakes) and it has been so fun. I've ran it with both 29" wheels (pictured here) and 27.5+ wheels - I personally prefer 27.5+ hands down. Its not that light, in fact I like to call it Heavy Metal!! (Insert rock hands here)
What I like about it:
- Pretty capable for a hardtail. I absolutely smash down rowdy trails and it can hold its own! Generally not as fast as a full squish bike, but its a steel hardtail that is a blast to ride. Not sure if its the steel frame or not, but it holds its own for sure. I definitely felt that the 27.5+ were more confidence inspiring on the downhill - better traction and feels like it lowers the bottom bracket a bit.
- Short chainstays make for a snappy bike, just pretty playful in general.
- Reynolds 853 Steel frame gives a lively feel on the trail. I would love to try a direct comparison of a non steel version (I know this doesn't exist) but does have a springy feel that is just fun to ride.
What I don't like:
- While I wasn't entirely concerned about the weight, it really is not a light bike (again, Heavy Metal). I think mine weighs in at 31-32ish lbs with my Crank Brother stamp pedals.
- Niner says it should fit 29" tires that are up to 2.5" depending on brand - a Schwalbe 2.35" Nobby Nic mounted on Industry Nine Trail 245 wheels practically do not fit and rubs on hard cornering. Seriously millimeters of clearance. For having Niner as a name and barely fitting a pretty normal size tire on not that wide of rims is a bit weak. No issue with plus size tires though!
If you're looking for a hardtail and are more concerned about having a rad time out on the trail than bother counting grams, this could be the bike for you! Feel free to reach out if you do have any questions on it or if you'd like any help putting together a custom build for yourself!