NINER SIR 9 Mountain Bike Frame


NINER SIR 9 Mountain Bike Frame


SKU: #BE2020966 Categories: ,
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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)
Frame Material
Reynolds 853 steel
Wheel Size
27.5+, 29in
Head Tube Diameter
1-1/8 – 1-1/2in tapered
Headset Included
Bottom Bracket Type
Cable Routing
internal dropper routing
Derailleur Pull
compatible with 34.9 sideswing front pull (front derailleur)
Brake Type
post mount disc, 180mm max rotor
Compatible Components
singlespeed with Niner Biocentric 30, 1x compatible (36t max ring), 2x compatible (26/36 or bigger)
Seatpost Diameter
Seat Collar
Rear Axle
12 x 148mm Boost thru-axle
Recommended Use
Manufacturer Warranty
5 years

Additional information


Large, Medium, Small, X-Large




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