Build Overview
This is a custom 2-Star Niner AIR 9 that we configured into a trail build. The stock AIR 9 2-Star is already a great value, but for this setup we made a few upgrades to push it toward a more capable trail bike. We’ve also built an XC version of this bike, which we’ll cover in a separate post.
The frame is Niner’s aluminum AIR 9—simple, durable, and easy to work on. The stock fork on the 2-Star build is already the Marzocchi Bomber Z2 at 120 mm, so that set the tone for turning this one into a more trail-focused configuration. We swapped wheels and tires, changed the brakes, and built it into a versatile, fun hardtail that still stays affordable.
These AIR 9s have been a mainstay for us. They’ve been reliable, easy to maintain, and customers put a lot of miles on them. This trail build gives riders another option depending on what style of riding they want to do.
Video
Full Build Specs
- Frame: Niner AIR 9 (aluminum, boost spacing)
- Cable Routing: Fully external brake + shift housing
- Dropper Ready: Yes (external entry, internal routing)
- Fork: Marzocchi Bomber Z2 (120 mm)
- Wheelset: Boyd Cycling Stumphouse (30 mm internal)
- Tires: Schwalbe Nobby Nic 2.4
- Drivetrain: Niner 2-Star build kit (details not provided in transcript)
- Brakes: Upgraded to 4-piston brakes (specific model not stated)
- Seatpost: Standard aluminum post (no dropper installed)
- Notes: Frame supports internal dropper routing
Build Notes
The AIR 9 aluminum frame is straightforward and easy to work on. Everything is external—brake line, shift housing—and you can unbolt every piece of housing off the frame in minutes. It’s boost spacing and uses thru-axles front and rear.
This frame also supports dropper routing. Even though we didn’t install a dropper on this build, the entry port is there, and the cable can be run internally. The choice to leave it out was simply to keep the price low and let the customer pick the exact dropper they want later.
The Marzocchi Bomber Z2 at 120 mm is the stock fork for the 2-Star AIR 9. It’s a little burlier than a standard XC fork but not as big as a true 140 mm trail fork. We’ve had excellent reliability with this fork—zero issues through a high volume of bikes—and it offers predictable cornering without the flex you get from lighter XC forks.
For the trail configuration, we swapped the stock 25 mm XC wheel for the Boyd Stumphouse 30 mm wheel and mounted 2.4 Nobby Nics. This gives the bike more traction and stability, especially for riders who want a more planted feel.
The brakes were also upgraded to 4-piston calipers. A lot of riders appreciate the added braking power on fast descents or in tighter singletrack, and it fits the trail theme well.
This build came out of a desire to differentiate the AIR 9 lineup. The stock configuration at $1,429 is tough to beat—and most big brands can’t match the value, especially with boost spacing and thru-axles. But when we had some AIR 9 frames arrive with Fox 32 Rhythm forks, and others with the Z2 120 mm forks, the idea formed: build one XC version and one trail version.
The result is a bike that fills a specific spot. Riders who want the extra fork travel and a burlier wheel/tire combination can go with this trail build. Riders who want something snappier and lighter can go with the XC build. Both use the same AIR 9 frame and both punch above their price range.
We enjoy building custom AIR 9s and dialing them in based on rider needs. With the frames and parts we currently have in the shop, we can offer several configurations at really strong price points.
Work With Us On a Custom Build
If you’re thinking about a custom gravel, MTB, or road build, we can help you spec it out and build it the way you want.