Bird Aether 9 review

Does Bird’s 130mm full-sus impress on the trails?

Our rating 
4.5 out of 5 star rating 4.5
GBP £3,850.00 RRP
Custom spec
The new Bird Aether 9.

Our review

The Aether 9 climbs well and descends like a hawk
Pros: Customisable spec; competitive pricing; stable under power; impressive descending capabilities
Cons: Some will want the cleaner look of internal cable routing, but external routing is a positive for home mechanics
Skip to view product specifications

Hot on the heels of the release of Bike’s first carbon bike, the Aether 9 C, the Aether 9 is a more wallet-friendly version of the company’s new 130mm trail bike. 


As you might expect from Bird, the geometry of the Aether 9’s aluminium frame is on the more ‘radical’ end of the scale, with long reaches and slack head angles, and at the point of purchase you have the option of modifying the specification to suit your riding needs or pocket depth.

Bird Aether 9 headtube
Bird’s bikes are designed in the UK.
Russell Burton / Immediate Media

My test bike came with a smattering of my favourite components. A 140mm Pike fork from RockShox, a Shimano XT drivetrain, carbon hoops from DT Swiss and aggressive Maxxis tyres to match the dank and dark muddy woods in which I’ve been testing the bike. For £3,850, we reckon this represents excellent value for money.

Bird says the Aether 9 is a bike that combines the best of modern mountain bikes: the front-end geometry of an enduro bike, pedal-friendly suspension and a short back-end to ensure it’s still a ton of fun, even 30km into a ride.

Bird Aether 9 frame and suspension details

The Aether 9 is the aluminium version of the carbon Aether 9C launched earlier in 2020. While the tube shapes are obviously different to its carbon sibling, the shape and purpose of the bikes are nigh-on identical.

The 130mm of travel is provided by a 4-bar suspension layout, with a droplink swinging from the top tube and seat tube junction pushing the shock.

The anti-squat characteristics have been designed with pedalling efficiency in mind. At 25% sag, there’s roughly 123% anti-squat in the highest 31:10 gear, and around 100% anti-squat in 32:51. This means the suspension should stay fairly static under normal pedalling loads.

Bird Aether 9 RockShox Super Deluxe
RockShox’s Super Deluxe shock has a piggy-back design, giving consistency over long descents.
Russell Burton / Immediate Media

As the bike progresses through its travel the anti-squat drops off, but not too significantly, meaning it’ll still give a fairly stable pedalling platform across its range of travel.

The leverage curve changes throughout its travel too. At the start of the bike’s travel, there’s a leverage rate of around 2.65, dropping to just below two at the end of the travel. This effectively means that early on there’s additional small-bump sensitivity, while later there should be more performance on bigger hits. There’s around a 30% progression through the stroke, to give support as you put weight through the suspension.

The alloy frame’s design will please home mechanics, with only the dropper post having any internal routing, while there’s also a threaded bottom bracket shell, ISCG05 mounts, 160mm post-mount rear brake and 31.8mm internal diameter seat tube.

Bird Aether 9 geometry

I’m 182cm tall and am testing a size large Aether 9. Bird’s approach to geometry has always been forward-thinking, with long reaches, slack head angles and steeper seat angles.

The Aether 9 is defined as a trail bike, yet still has the long and slack front-end. However, differentiating it from Bird’s AM9 enduro bike is a shorter ‘snappier’ rear end, a little less travel and a slightly perkier feel.

Bird Aether 9 cockpit
A 40mm stem holds a wide bar, ideal for muscling around tight trails.
Russell Burton / Immediate Media

At 506mm, the reach on the large is as big (if not bigger) than many brands’ XL size, and this is paired with 430mm chainstays across the sizing range. With increasing front-end length but a static rear, the front-to-rear ratio will change with sizing. Seat tubes are short, though, allowing one to consider sizing up or down to suit your preference.

The range starts with the medium size, and there’s a medium long before the large and XL. These give reach figures of 462mm up to 527mm, with corresponding seat tube lengths of 395mm to 470mm. Seat tubes are purposefully short in order to enable riders to fit 200mm dropper posts, should they wish.

SizeMediumMedium LongLargeExtra Large
Reach (mm)462484506527
Stack (mm)625634643652
Head tube angle (degrees)65656565
Seat tube angle (degrees)77.17776.976.9
Seat tube length (mm)395420445470
BB height (mm)330330330330
Wheelbase (mm)1212124012651292
Chainstay (mm)430430430430
Top tube (mm)605630655680
Standover (mm)699700700704

Bird Aether 9 specifications

Bird’s online purchasing system allows for plenty of customisation of the kit on the bike. 

As such, there are a number of example specifications upon which your particular bike could be based. These start with the £2,600 ‘Wallet Friendly’ build, with a Pike Select+ fork, Deluxe Select shock, DT Swiss M1900 wheels and a full Shimano Deore groupset.

Higher-priced options include the ‘Brawler’, which is built with some burly parts, including Fox 36/DPX2 suspension and super-sticky tyres for £4,390. And, there’s the ‘Light on the Scales’ build, with parts selected to keep the weight nice and low – this has a SRAM XX1 drivetrain and Maxxis Rekon tyres, at £4,670.

My bike arrived with some pretty top-end parts plugged into the aluminium frame, including carbon hoops from DT Swiss, Ultimate-level suspension from RockShox, a full Shimano XT groupset and a mix of finishing kit including RaceFace, Gusset and Bird’s own parts.

Bird Aether 9 pike fork
The RockShox Pike Ultimate, in its 140mm guise, is an excellent fork.
Russell Burton / Immediate Media

The range of kit on offer includes everything from Hope-hubbed alloy wheels, through to RockShox’s Select-level suspension, Hope/SRAM/Shimano brakes and most tiers of groupsets from SRAM and Shimano.

When specifying the bike with Bird, I also requested the Maxxis Shorty/Minion DHR II tyre combo to match the conditions I expected to test the bike in. And I’m glad I did, as the British autumn and winter lived up to its reputation.

Bird Aether 9 ride impressions

I mostly rode the bike on my natural, hand-made trail test loops, with plenty of roots, some rocks, along with berms, jumps and big compressions.

I also spent a little time on some rougher, more formalised DH tracks, as well as a quick rip around a trail centre. Setting up RockShox’s suspension is always very easy, and I had no issues with any of the components fitted.

Bird Aether 9 climbing performance

With the chain midway up the cassette, the anti-squat does a good job of keeping the rear-end fairly static under normal pedalling loads. There’s a little pedal-induced bob, but not enough to greatly impact on how efficient the bike feels under power.

With the rear wheel free to move up and over small trail imperfections, and the seat angle steep at around 77 degrees, the Aether 9 is a very competent climber. In its lowest gears, the additional anti-squat does stiffen the bike over square edges, but I didn’t find it lurched badly as it crests them.

Bird Aether 9 Maxxis tyre
Maxxis rubber mounted to a 30mm-wide rim  all good!
Russell Burton / Immediate Media

The grip afforded by the Minion tyre at the back means I never found myself scrabbling around for climbing traction, and with no noticeable jerk as the rear wheel crests a rocky or rooty step, I found it very easy to maintain a smooth pedalling rhythm.

When stood on the pedals, there is inevitably some pedalling bob. However, again, it rarely left me feeling like I was riding through treacle. The Super Deluxe Ultimate shock does have a compression switch, enabling you to lock the shock out on smooth, tarmac drags – something I took advantage of when advantageous, as the grippy rubber at the back does rob a little speed at times. Though, of course, riders who prefer a faster-feeling ride could spec a less aggressive rear tyre.

Bird Aether 9 rear brake
Shimano’s 4-pot XT brakes performed well in testing.
Russell Burton / Immediate Media

Despite the fairly steep seat angle, the longer top tube and reach mean is plenty of real estate over the bike, opening up my chest, and allowing for plenty of fore-aft body movement to manage rear-wheel grip and front-end steering accuracy on steeper drags.

Bird Aether 9 descending performance

Despite being marketed as a trail bike, there’s no doubt the Aether 9 is a hugely capable descender.

With ‘only’ 130mm of travel, it is noticeable over the biggest hits that there’s less suspension that some longer-travel trail or peppy enduro bikes, such as the new Canyon Spectral that I rode alongside the Aether 9. 

However, despite pushing the bike towards the endpoint of its 130mm travel, it never felt unsettled. The ramp-up is smooth and controlled, and the Super Deluxe is more than capable of handling bigger and repeated hits. I never found the travel to be holding me back during testing.

This is helped too by the bike’s shape. The long geometry puts plenty of distance between the axles, despite the shorter back-end, meaning high-speed and steep terrain stability is ample, while the 430mm stays do seem to keep the bike eager enough to chop and change direction. 

Bird Aether 9 riding shot
The Aether 9 is long enough to give plenty of stability, but isn’t a barge, either.
Russell Burton / Immediate Media

The front geometry is clearly borrowed from an enduro bike, and while we reckon this is a trail bike that could happily tackle UK enduro racing, that short back-end may compromise ultimate high-speed racing performance a touch. Here, though, it has to be said that this is not the bike’s modus operandi.

I happily rattled the Aether 9 through the steeper, muddier tracks encountered during testing, and I also took it to some of the Forest of Dean’s downhill tracks – far more beaten in and beaten up.

Bird Aether 9 chainguide
Our test bike came with an MRP chainguide and bash.
Russell Burton / Immediate Media

The suspension dealt well with medium-sized hits, as well as repeated over-root chatter. There’s a fine balance between a soft, soggy sofa-like ride, and one where every impact is transmitted through the bike, and the team at Bird seems to have found that balance point well. There’s a gentle patter as you traverse rocks and roots, and the system feels incredibly composed over mid-sized hits.

When it comes to smoother tracks, there’s just enough support through the back-end to allow you to push and pump, without breaking into a soggy mid-stroke, and as such, I happily found myself generating speed on rolling trail centre terrain.

When it comes to cornering, the Aether 9 seems to love dropping into steep, muddy, rutted corners. The BB sits 40mm below the axles at rest, so lower when sagged and pushing through a corner. This helps keep weight low and I found it very easy to drop the bike onto its shoulder treads. 

Bird Aether 9 descending
The rear suspension performance is excellent.
Russell Burton / Immediate Media

The aforementioned short stays again mean it felt happy on snaky slalom-type tracks. The 65-degree head angle isn’t so slack as to make it feel too much of a handful on flat trail centre tracks either. 

Bird Aether 9 bottom line

In the build tested, I probably wouldn’t choose to just smash trail-centre laps day after day on the Aether 9. Instead, the aggressive build worked really well on the steep, woody and muddy tracks that the south-west has in abundance. Fortunately, with Bird’s flexible approach to speccing, there should be a choice for most riders, depending on where you ride.

The rear suspension feels excellent, though I’m looking forward to spending more time on the bike, pitching it against more of its competitors back-to-back, over ever-more varied terrain. We may even have a chance to try it with a coil shock, down the line.

The geometry is spot on, too – long and slack enough to be authoritative on the trail, but not so much that it feels like an oil tanker in tighter situations.

Bird Aether 9 cable routing
External cable routing is very, very easy to work on.
Russell Burton / Immediate Media

I’ve heard comments that the unpainted and externally-routed frame finish isn’t as aesthetically ‘polished’ as that from other brands, though, in my opinion at least, that’s not a deal-breaker. And from a maintenance point of view, external cables are great. 


Ultimately, it’s how well the bike rides that should be the defining factor of its performance. And after a few weeks with the Aether 9, I’d say Bird has largely hit the capable trail bike nail on the head.

Product Specifications


Price GBP £3850.00
Weight 14.9kg (Large)
Year 2021
Brand Bird


Available sizes Medium, Medium-Long, Large, Extra Large
Rear derailleur Shimano XT
Tyres Maxxis Shorty 29x2.5in f, Maxxis Minion DHR II 29x2.4in r
Stem Bird
Shifter Shimano XT
Seatpost BikeYoke Revive
Saddle Fabric Scoop
Rear Shocks RockShox Super Deluxe Ultimate
Headset Hope
Bottom bracket Shimano XT
Handlebar RaceFace Next R
Fork RockShox Pike UItimate
Cranks Shimano XT
Chain Shimano XT
Cassette Shimano XT
Brakes Shimano XT
Wheels DT Swiss XMC 1501