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Bird Aether 9 review

Bird's Aether 9 is crowned our 2021 Trail Bike of the Year

Our rating 
4.5 out of 5 star rating 4.5
GBP £3,850.00 RRP
BikeRadar Trail Bike of the Year 2021 – Bird Aether 9

Our review

Whether you’re pinning it downhill or stretching your legs on the climbs, the Aether 9 delivers
Pros: Excellent geometry, with options to fit riders of all sizes; exceptional value for money; sorted rear suspension that works perfectly in nearly every situation
Cons: There’s smoother out there over high-frequency stutters
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The Aether 9 is the newest addition to Bird’s flock of bikes, being the aluminium version of the Aether 9 C that launched in the middle of 2020, and sits alongside the Aether 7 that podiumed in last year’s Bike of the Year test. This time round, however, Bird has taken the top spot to secure our coveted Trail Bike of the Year prize.

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The Aether 9 could easily have trod on the toes of the 150mm AM9, especially considering the geometry of the bike (which we’ll talk about later), however with a touch less travel and a tighter back end, Bird has managed to build a bike that’s noticeably different from its almost identical (looking) sibling.

Combine that excellent geometry and sorted suspension with top value for money and you have a bike that truly does it all, making the Bird Aether 9 a worthy winner of the trail category in our 2021 Bike of the Year test.

Bird Aether 9 frame and geometry

While the carbon Aether 9 C gets all the bells and whistles that a carbon bike is expected to have, the aluminium Aether 9 is refreshingly no-nonsense in its construction.

The most obvious is the external cable routing – a real boon for those of us who are maintenance-phobes and benefit from the easiest of cable routing setups.

The welding on the Bird Aether 9 full suspension mountain bikes is not very smooth
Bird certainly doesn’t hide its alloy construction welds.
Russell Burton / Immediate Media

With the shock entering into the top tube, there’s space for a bottle above the down tube, and I fitted a Fidlock bottle system which left just enough room for the piggyback shock and a 590mm bottle.

Around the bottom bracket there’s a removable ISCG-5 mount, should you wish to ride with a bash guard or chainguide.

The 130mm of suspension is dolled out by a four-bar linkage that Bird says has been tuned for pedalling efficiency via higher anti-squat figures, while the progression and mid-stroke support are there to give pop and control on the descents.

Known for long and slack geometry, it’s no surprise to see Bird’s Aether 9 is one of the more radical bikes in our 2021 Trail Bike of the Year test – and in fact, in our best trail mountain bikes list too.

My large frame has an impressive 507mm reach, 65-degree head angle and short 430mm chainstays to give a wheelbase of 1,262mm.

The seat tube sits at 77 degrees and is nice and compact at 445mm, so at 182cm I could easily live with the longer dropper posts on offer.

Seat angle (degrees)77.17776.976.9
Head angle (degrees)65656565
Chainstay (cm)43434343
Seat tube (cm)39.54244.547
Top tube (cm)60.56365.568
Head tube (cm)1121314
Bottom bracket drop (cm)4444
Bottom bracket height (cm)33333333
Wheelbase (mm)1,2121,2401,2651,292
Standover (cm)69.9707070.4
Stack (cm)62.563.464.365.2
Reach (cm)46.248.450.652.7

Bird Aether 9 kit

Usually we have a £3,500 limit on our Trail Bike of the Year contenders, but with Covid, Brexit and massive supply and demand pressures, our test bike came in at £3,850.

However, Bird is one of a growing number of companies that offers an element of customisation as part of the ordering process. So, while my test bike came specced with a very nice pair of DT Swiss EXC 1501 carbon wheels – with a 30mm internal rim width and understandably lightweight – swapping these for a Hope Pro4-hubbed, alloy DT Swiss XM481 wheelset would drop the price to £3,455.

Carbon DT Swiss hoops are an option at the checkout
Carbon DT Swiss hoops are an option at the checkout.
Russell Burton / Immediate Media

Or, you could drop it further to £3,310 by choosing a pair of DT Swiss M1900 wheels.

Both of these wheelsets also have 30mm internal width rims, but add approximately 400g to the overall build.

Aether 9 builds start at £2,515.40.I briefly rode the bike with a pair of DT Swiss M1900 wheels from a different bike and while there’s some additional weight – largely in the rims – which does ever so slightly dull snappiness under power, the ride quality wasn’t too far away from the EXC 1501 wheels. I still preferred the performance of the Bird with the fancier hoops in place, though.

The Bird Aether 9 full suspension mountain bike is equipped with Shimano XT four-pot disc brakes
Shimano’s four-piston XT brakes are a fine choice.
Russell Burton / Immediate Media

As part of the customisation process, I asked for the bike to be specced with a Shimano XT drivetrain and my preferred Maxxis tyres for winter woodland testing – a Minion DHRII at the back and a Maxxis Shorty at the front, both in their Wide Trail carcasses and sticky rubber.

Suspension duties were taken care of by RockShox’ 140mm Pike Ultimate fork and Super Deluxe Ultimate shock.

The Bird Aether 9 full suspension mountain bike is equipped with a RockShox Super Deluxe Ultimate rear shock
The top-spec air shock from RockShox keeps the rear wheel in check.
Russell Burton / Immediate Media

Bird Aether 9 ride impressions

Last year the Bird Aether 7 came third in our Trail Bike of the Year test. The alloy bike impressed us most on tight, twisty tracks, but we felt its 27.5in wheels let it down over the rough stuff. What we really wanted was the same super-capable chassis but with bigger 29in wheels.

And boy, did Bird deliver. The Aether 9 takes the steadfast pedalling, ultra-capable shape and sorted suspension of the Aether 7 and gives it that smooth riding, mile-munching and corner-railing performance that big wheels offer.

Bird is known for its use of longer geometries, and the Large Aether 9 certainly follows this trend. With a reach stretching to 507mm and a head angle of 65 degrees, the front wheel is well ahead of the low-slung bottom bracket, with all the high-speed capabilities that entails.

At the back, though, the 430mm chainstays are tight, keeping the rear wheel tucked into the frame, which allows you to easily get your front wheel up in the air and pull the front wheel around tight corners.

Cyclist in red and black riding the Bird Aether 9 full suspension mountain bike downhill
The bike is very long and very low, so it corners on rails.
Russell Burton / Immediate Media

As a result, the Aether 9 is in its element on steep, twisty, rough and loose trails. Unflappable in its attitude, the bike lets you instantly pick lines or hold on and grip the bar until you hit the fire road below.

On slow, super-tech descents the calm support when you plant the rear wheel into the catch-berm bolsters your confidence in the bike.

There is a bit of payback from all this length when you’re tired and need to get the front end moving because longer bikes need exaggerated body movements to make them react, but the compact rear end gives the Aether 9 the edge over similarly long bikes when it comes to manoeuvrability.

Should that 500mm+ reach be just too much, the Medium Long size, between the Medium and Large would also have suited me at 6-foot, with its 484mm reach and super-short 420mm seat tube.

BikeYoke's Revive droppers come in a wide range of lengths, including this monster!
BikeYoke’s Revive droppers come in a wide range of lengths, including this monster!
Russell Burton / Immediate Media

If I was purely looking at downhill capability, the 130mm of travel at the back is noticeably less than the 150mm offered on many other similarly-shaped trail bikes. However, with ample progression through its stroke, it was rare that the Bird struggled with the biggest impacts.

At times there’s a touch more feedback under braking, over roots, when ridden back-to-back with the smoothest bikes around, but with a stretched-out front end I never found that that led to a feeling of being out of control. What I did like though was how composed the suspension was.

Cyclist in red and black riding the Bird Aether 9 full suspension mountain bike downhill
Smiles for miles. Not only is the Aether 9 a hoot to ride, it’s efficient enough that getting the miles in isn’t too painful.
Russell Burton / Immediate Media

As long as you’ve got the front wheel nicely weighted, the Aether 9 is excellent on flatter, more mellow trails because the rear suspension is rock-solid under pedalling, and really allows you to pump and drive the bike through rises and rollers.

Jabbing at the pedals was rewarded with bursts of speed, almost reminiscent of an XC bike, despite the Minion/Shorty tyre combo that I specced when picking the build.

Up hills I had nothing to complain about, with the steep 77-degree seat angle, less sag than longer travel bikes and solid under power suspension robbing very few of my precious Watts.

There’s plenty of space between the saddle and the bar to ensure your body weight is in the right place too, to balance rear wheel grip and front wheel precision. Plus, the shorter chainstays help when you need to lift the front wheel up a step or scrabble around a tight uphill switchback.

Cyclist in red and black riding the Bird Aether 9 full suspension mountain bike downhill
Despite having less travel than some trail bikes, the control offered out back means I rarely felt the bike was out of its depth.
Russell Burton / Immediate Media

It’s not just excellent ride quality that’s needed for a bike to win Trail Bike of the Year, though. While it is a touch over our usual budget, Bird still offers exceptional value for money.

No doubt using alloy rather than carbon saves a chunk of cash – and that’s cash I’d prefer spent on parts than the frame – but the Ultimate level suspension from RockShox is not to be sniffed at, nor is the full Shimano XT groupset.

Ultimately, the DT Swiss EXC 1501 wheels are the item that drags the Bird over budget, but as mentioned, a cheaper, yet still more than acceptable pair of DT Swiss alloy hoops would bring the cost right down and not have a huge impact on how the bike rides.

Yes, carbon frames are very pretty to look at, but I appreciate the user-friendly approach Bird has to building its chassis, and the external cable routing and threaded bottom bracket make access to adjusting and replacing bearings and pivots much easier.

All these items help make owning a bike much easier, in my opinion.

Bird Aether 9 overall

Angled pack shot of the Bird Aether 9 full suspension mountain bike
The Bird Aether 9 is our 2021 Trail Bike of the Year.
Russell Burton / Immediate Media

Picking our 2021 Trail Bike of the Year winner has been a real struggle. The Canyon Spectral was, arguably, the most sorted frame on test and the Saracen Ariel 30 Pro was really good value, and I loved its approach to geometry.

Both YT’s Jeffsy Blaze and Propain’s Hugene deserved a podium position too, being super enjoyable and incredibly all-rounded in their performance respectively. Perhaps the heart picks the YT, while the head the Propain.

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Ultimately, though, the Bird just pipped them all to the line. The Aether 9 delivers in every situation, whether it’s a long day in the hills or short blasts in the woods. From its geometry to its suspension, and value to live-ability, it’s hard to look past the Bird Aether 9.

Thanks to…

A massive thank-you to BikePark Wales for granting us access to its trails despite the bike park being closed to the public.

Cheers also to Fox clothing for sorting the kit for the photo and video shoots and Garmin for sorting us out with bike computers to log the many miles of testing.

And not forgetting Muc-Off, for its help keeping the bikes washed and lubed throughout testing.

Product Specifications


Price br_price, 5, 3, Price, GBP £3850.00
Weight br_weight, 5, 6, Weight, 14.78kg (L) – without pedals, Array, kg
Brand br_brand, 5, 10, Brand, Bird


Available sizes br_availableSizes, 11, 0, Available sizes, M, ML, L, XL
Bottom bracket br_bottomBracket, 11, 0, Bottom bracket, Shimano XT
Brakes br_brakes, 11, 0, Brakes, Shimano XT 4-pot, 203/183mm rotors
Cassette br_cassette, 11, 0, Cassette, Shimano XT
Chain br_chain, 11, 0, Chain, Shimano XT
Cranks br_cranks, 11, 0, Cranks, Shimano XT
Fork br_fork, 11, 0, Fork, RockShox Pike Ultimate 140mm
Frame br_frame, 11, 0, Frame, Aluminium
Grips/Tape br_gripsTape, 11, 0, Grips/Tape, Gusset
Handlebar br_handlebar, 11, 0, Handlebar, RaceFace Next R 780
Rear derailleur br_rearDerailleur, 11, 0, Rear derailleur, Shimano XT
Rear Shocks br_rearShock, 11, 0, Rear Shocks, RockShox Super Deluxe Ultimate
Saddle br_saddle, 11, 0, Saddle, Fabric Scoop
Seatpost br_seatpost, 11, 0, Seatpost, BikeYoke Revive 200
Shifter br_shifter, 11, 0, Shifter, Shimano XT
Stem br_stem, 11, 0, Stem, Bird 45mm
Tyres br_tyres, 11, 0, Tyres, Maxxis Shorty 29x2.5 WT 3C EXO f / Maxxis Minion DHRII 29x2.4 WT 3C EXO
Wheels br_wheels, 11, 0, Wheels, DT Swiss EXC1501 rims; DT Swiss 240 hubs