Bird Aether 9C Review



Words by Robert Johnston
Photos by Adam McGuire

UK based Bird Bikes have been making waves with their aggressive geometry bikes with surprisingly reasonable price tags thanks to their direct-to-consumer model. They’ve typically stuck to metal for their frames to keep up the great price points, however as their bikes have grown in capability, they’ve been looking for ways to further boost their performance. Carbon Fiber proved to be the answer in this case, to optimize the weight and stiffness of the frame and create an all-round better performer out on the trail. Enter the Aether 9C, an aggressive geometry trail bike with a stout and shapely frame that adds Carbon fiber to the Bird portfolio.

We were able to steal the personal bike of Clark at North-East Scotland’s Bennachie Bike Bothy bike shop, who have a unique setup with Bird that benefits both parties and set to work putting the Aether 9C to the test on the trails surrounding the shop for a few weeks.


• 130mm Horst Link Suspension
• HTA 65°
• STA 76.2° (effective)
• REACH 484mm (ML)

Price: £4,500/$6,000 (as tested)

Bird began the Aether lineup with two aluminum framed offerings, both of which shared a playful character whilst retaining some all-day friendly pedaling traits. For this kind of bike, which would see a huge variety of use from XC mile crunching through to jump line playing, the strength had to be made sufficiently high to ensure there weren’t any failures which added a little more weight than a less aggressive rider might desire. Carbon fiber then seemed like an obvious choice to maintain the strength, whilst adding stiffness and shaving off roughly 250g from the frame weights (claimed). The suspension and geometry was maintained as they were happy with it, but the design was changed radically otherwise to make best use of the new material, and so the Aether 9C was born.

Bird Aether 9C Profile Shot

Following on from the Aluminum version, the Carbon Aether 9 uses a Horst link suspension design to deliver 130mm of rear wheel travel, which is paired to a 140mm fork up front as standard. The 9 denotes the wheel size in the Aether range, with the 9C designed to run 29” wheels on both ends and no option offered to tweak things for a mullet configuration. Bird has a more speed and race-oriented range of enduro bikes in their Aeris, so the Aether line up is tailored more towards “fun”, with geometry that Bird selected to ensure there’s still an element of agility thrown into the mix.

Bird is one of the more “hush hush” proponents of the longer reach craze that I’ve yet to come across. I was aware that their bikes tended towards the stretched-out end of the spectrum but hadn’t been aware of quite the extent to which they had gone, until I was asked which size I’d like to test. The Aether 9C is available in sizes Medium through to Extra Large, which spans reach numbers beginning from 455mm on the Medium through to a whopping 541mm on the XL. Bird suggests this will suit a range from 5’7” (170cm) through to 6’4” + (193cm+), with the ideal size for my 6’2” height being the Large with option to size up or down. You may already know that we’re not fully on board with the huge reach numbers at The Loam Wolf, and so I was glad to find a “Medium Long” (ML) size in their lineup, sporting a 484mm reach with just a 420mm seat tube. This seat tube is straight for a very long portion, to the point that a 200mm dropper could be slammed in my ML and many will slam in a medium too.

Bird Aether 9C Rear Triangle

The lengthy reaches is where the out-there geometry ends though, with the remainder of the numbers sounding quite reasonable for the intended aggressive trail category. Shared between the full-size range are the 65-degree head angle, slammed 40mm BB drop, and compact 430mm rear end – there’s no size-specific rear ends here. Seat tube angles are size specific however, to keep the climbing weight balance more consistent for taller riders on the bigger sizes. The actual angles increase one degree per size from 71° for the medium through to 74° on the XL, and the offset produces effective angles from 76.5° (M) to 78° (XL). The low BB gives some relatively high stack figures, ranging from 625mm to 652mm; and the long reach figures put the wheelbase at a limo-esque 1301mm for the XL, dropping to a more reasonable 1235mm for the Medium Long tested.

Bird continues to tweak their Horst Link kinematics to produce their desired ride characteristics, and the Aether range sees Anti Squat numbers that increase as you work your way down the cassette, offering more support when you’re inputting more force in the harder gears and avoiding loss of traction towards the larger end of the cassette. Anti-Rise falls from roughly 70% at sag down to almost 0% towards the end of the travel, keeping the rear end moving freely for bigger compressions but preserving the geometry relatively well in a more neutral position. The leverage ratio is progressive throughout with roughly 30% progression through the travel, making the Aether 9C coil friendly or suitable for high volume air shocks.

Bird Aether 9C Rear Triangle

The frame tested was a pre-production model, featuring a few minor differences to the version you would purchase right now. The first of these is the cable routing, which is fully internal and guided on the production model and features a Y-connector at the head tube to allow for a rear brake on either side of the bar. The second is the chainstays, which have been pulled in to avoid the heel rub that plagued the tested frame in a past life. I’m quite a neutral-footed rider so don’t often suffer from heel rub issues as it is, but prospective customers need not worry for clearance on the production model. These stays will still allow for up to a 2.6” tire in the rear without compromising mud clearance too much. Retained from the pre-production frame are the replaceable alloy inserts for the frame pivots, ensuring failed hardware doesn’t render the frame useless; and locking collets on the main and rocker-seat stay pivots to reduce the likelihood of them rattling loose. Keeping home mechanics happy is a threaded BB surrounded by ISCG-05 tabs. Similarly, the headset bearings sit directly into molded carbon seats to avoid concerns over pressing the cups into the frame. SRAM’s Universal Derailleur Hanger (UDH) allows for replacements to be sourced easily on the road. There are generous rubber guards on the downtube, chainstay and seatstay with the Bird logo imprinted for a classy touch. The bottle mounts on the inside of the downtube have enough room above for a huge bottle with a piggyback shock thanks to the purposely shaped downtube. The rear brake mount is a 160mm post mount, offering compatibility with up to a 180mm rotor with the correct adaptor.

Bird takes advantage of their direct-to-consumer business model to offer customers the chance to fully tailor the spec of the bike to their preferences, with a selection of different brands and component levels on offer. Frame-only options are available, with the bare frame with axle going for £1,740/$2,317 and a range of shock options from the £160 RockShox Deluxe Select+ through to the £800 Fox DHX. Full builds are available in a SRAM or Shimano base-spec from roughly £2,900/$3,900, through to £6,400/$8,500 or more if you really try to throw money at it. The spec tested would retail for roughly £4,500/$6,000, with aggressive riding capability kept in mind throughout leading to a total weight of 14.9kg/32.9 lbs with Cushcore inserts in both ends. A RockShox suspension combo of a 140mm travel Pike Ultimate up front paired to a Deluxe Ultimate in the back offers a lightweight package that doesn’t skimp on quality. Shimano’s XT 12spd gearing with XTR rear mech provides the Hyperglide+ shifting tech, with a hardy crankset built to take a beating through the granite rocks that surround the Bennachie Bike Bothy HQ. The brakes continue the Shimano theme with the 4-pot XTs running on floating rotors. The Cushcore inserts were fitted in a set of Maxxis EXO+ tires, offering protection to the Hope Pro4 on Dt Swiss EX511 wheelset. A Bird Down dropper provided 200mm of drop for the Fabric Scoop seat. The cockpit featured a Race Face SixC bar clamped by a Unite Components Renegade stem.

Bird Aether 9C Action

I collected the Bird Aether 9C from Bennachie Bike Bothy, who helped me get the ballpark setup dialed in quickly. It proved to be an easy bike to set up – there’s not an insane amount of tunability in the suspension package, but we got to a good place very quickly with a quick sag set up and few clicks here and there of the rebound. After the first few rides the weather played ball and I was able to link up my Motion Instruments suspension telemetry kit to get things dialed in further, leading to slightly more fork pressure and slightly faster rebound out back, but the base settings had put us in a surprisingly good place.

On the way up the hill the Bird is a pleasant enough machine, but it’s not ultra-supportive for pedaling, especially when standing up and mashing the pedals on a slow and tech climb. This does let the rear end conform a little more, meaning that seated efforts generate a healthy amount of grip on rock and root infested ascents, but I began to use climb switch more often near the end of the test for all but the most chundery of climbs to obtain a more efficient platform. Thankfully the climb switch is very easy to reach when on the move, encouraging its use to tailor the suspension performance to the terrain ahead. When climbing tech, the position is reasonable, the grip generated is good and there’s adequate weight on the front wheel even with those slammed chainstays to prevent it from being too much of an issue, until you hit a very steep pitch in the easiest gear or try to accelerate hard round an uphill switchback. There’s no doubt my leg length and accompanying seat height will have exacerbated this effect, with my saddle ending up more rearward than their relatively steep 77° effective angle claimed. Larger frame sizes will suffer from this less, thanks to that steepening actual seat tube angle, but nonetheless I don’t imagine I’ll be the only 6’2” (189cm) rider to opt to “size down” to the Medium Long size. I pushed the saddle forward in the rails to offset the slightly laid-back post and ended up in a comfortable position, which formed a good balance of front wheel weighting without cramping the cockpit. I had been concerned that such a low bb would make pedal clearance suffer when on the gas, but thanks to the increasing anti squat moving down the cassette it proved to be ample, if not incredible. As with pretty much any modern bike there were still a couple of pedal scraping moments on some tech climbs, but thankfully the descents didn’t present any issues. The weight of the bike tested was higher than I’d imagine almost anyone building one of these, with a burly wheelset and the full-fat Cushcore inserts adding considerable heft to the most detrimental place, and so the acceleration was certainly lacking. I spent a few rides with a lighter weight wheelset running EXO+ tires without inserts, which improved things considerably and left the Bird feeling much more agile, but even with that heavy wheel setup the Aether wasn’t a bike I was scared of putting in the miles on.

Bird Aether 9C Action

On the descents, not only was catching pedals not an issue, but rough terrain sensitivity and bottom out resistance proved to be without issue too. 130mm of rear travel can feel like a whole lot more when it’s managed well, and the Aether manages it very well indeed. It took three weeks of me running it at 28-30% sag to get a single harsh bottom out, riding enduro and downhill tracks as if I was on a longer legged machine. And the tracking was stellar too – the eagerness of that first 50% of the travel to eat up the bumps, with a slight increase in progression in the mid stroke to give extra support works really well with the relatively linear Deluxe Debonair shock to provide an all-round capable rear end. That supportive mid stroke produces a platform from which to pump and pop easily, combining with that short rear end to offer a playful character. Though I certainly didn’t take the Aether down any enormous descents, there was no sign of lost support or increased rebound speed that could be caused by an overworked shock, much to my surprise with the size of it looking somewhat out of place with the burly frame tubes surrounding.

The geometry is the one element of the Aether 9C that didn’t surprise me – you can see it’s general bias from just looking at it. The 484mm reach number I’d selected felt familiar, but the compact rear end was a different experience to the majority of the current crop of aggressive trail machines. The resulting balance on the descents provided some distinct handling traits – not all bad – that required a slightly different approach to body weight management in certain scenarios in order to unlock the most speed and grip. The default body weight bias is slightly rearward, which gives a safe feeling that keeps the front wheel slightly light through rough terrain and lets the fork pick its way through the trail, aided by a slack enough head angle and that low bb producing a stable ride. This is great in janky, chunky rock gardens and in steeper pitches of trail, but in long flat or off-camber turns it necessitates an active riding approach to maintain front end traction. That shorter rear end and slammed bb make bermed corners a riot, especially the slightly tighter ones that need a “slap” rather than a patient carve around. A small amount of body movement quickly translates weight to the rear tire, which encourages a “steer from the rear” sort of technique. Certainly not the fastest way around a corner most of the time, but definitely one of the more fun approaches. The frame stiffness out back is high for sure but paired with a slightly de-tuned spoke tension it offered ample compliance to the terrain and produced no issues with off-camber grip, whilst avoiding any vague sensations when squaring off turns.

The burly spec list proved to be flawless throughout testing as you may expect – Shimano’s 12spd gearing is simply fantastic once bedded in; the brakes were consistent and predictable though ever so slightly short on ultimate stopping power; and the rest of the kit was issue free. There was one incident with the rocker pivot bolt breaking, which was suggested to have been caused by it being under torqued, but the replacement presented no further issues, and I was assured by sources I consider trustworthy that it was a freak occurrence. Having a decent grasp of the consensus of Bird bikes in the UK, I don’t think there’s any cause for concern with their build quality in general.

Bird Aether 9C Action

The Wolf’s Last Word

Really all the traits of the Bird Aether 9C point it towards being a longer legged bike. It’s stable and sensitive and encourages some highly aggressive riding in rough and technical terrain, especially for a 130mm travel bike, but the climbing platform is not quite as firm as some of the competitors, losing a small amount of efficiency and “pep” as a result. You could maybe add a remote lockout to improve the pedaling traits, but the short of it is that the Aether 9 is simply more bike than Bird perhaps intended it to be, and I’m sure not complaining about it.

Price: £4,500/$6,000 (as tested)
Weight: 14.9kg/32.9lbs (ML / custom build)


Frame: Carbon Fiber; 130mm
Fork: RockShox Pike Ultimate 140mm, Boost
Shock: RockShox Deluxe Ultimate, 210×55

Brakes: Shimano Deore XT 4pot, 200F/180R RT86 rotors
Handlebar: Race Face SIXC, 35 x 800 mm, 20mm
Saddle: Fabric Scoop, CrMo
Seatpost: Bird Down Dropper, 31.6 x 200mm
Shifter: Shimano XT, 12s
Stem: Unite Renegade, 35 x 40mm

Rims: DT Swiss EX511, 30mm
Hubs: Hope Pro4, 15×110/148×12
Front Tire: Maxxis Shorty, EXO, 29″ x 2.5″
Rear Tire: Maxxis Assegai, EXO+, 29″ x 2.35″

Bottom Bracket: RaceFace Threaded
Cassette: Shimano XT 12s; 10-50T
Cranks: Shimano XT, 32T, 170mm
Derailleur: Shimano XTR; 12s

Bird Aether 9C Rear Forward Link

We Dig

Capability beyond its numbers
Climbing grip
Stiffness balance
Loves back wheel

We Don’t

Rearward weight bias (sometimes)
Not the Best at Pedaling


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