bird aeris 9

Bird Aeris 9 review

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The Bird Aeris 9 is a 160mm travel full suspension 29er made out of aluminium. Designed, specced and assembled in Britain.

bird aeris 9

It doesn’t seem that long ago since Bird first started out with its 27.5in wheel Aeris, but somehow Bird is celebrating its tenth(!) anniversary in 2023. This Aeris 9 is not the ninth incarnation of the Aeris. The 9 refers to the wheel size, namely 29in. Bird has something of a stellar reputation amongst experienced mountain bikers in the UK. Indeed, Bird was right up in the ‘most desired’ brands in our recent reader survey. It seems Bird bikes really strike a chord with riders looking for hard-riding, well-specced bikes without massive price tags. And Bird knows how to make a bike look cool too. Which helps.

The Bike

The Bird Aeris 9, like the other two bikes in this test, is a 160mm travel full suspension 29er made out of aluminium. Designed, specced and assembled in Britain, Bird describes the Aeris 9 as an ‘All Mountain’ bike and I’m all for it. I’d much rather use the term All Mountain than something disgusting like ‘Aggressive Trail’ (ugh). If you wanted to further up the ante, the Aeris 9 can be morphed into a big ol’ 180mm travel beastie via an optional linkage. Even if you were to never feel the need up your ante, it’s reassuring to know that the Aeris 9 chassis is built strong enough to handle such rigours. Even just sticking with the original linkage, there is a flip chip in the Horst Link chainstay pivot location. Flipping it makes the bike 0.5° slacker, 7mm lower and 6mm longer (chainstay length).

Bottle friendly

The build kit is worth discussing. Partly because this is a group test of mail order mountain bikes. But partly because it has a massive effect on the whole experience of riding this bike. Basically, the build kit is perfect. Coil rear shock, Zeb Ultimate, Formula 4-pots, 200mm dropper, nice grips, big bars, short stem, DHF ’n’ DHR II rubbers. The drivetrain is fairly yadda-yadda in my opinion. All SRAM and Shimano drivetrains work amazingly once above base-level. But great bits ain’t worth diddly squat if the geometry is ropey. The headline stats here: 63.6° head angle, 77.5° seat angle, 486mm reach (size Medium–Long), 343mm BB height, 440mm chain stays. They all sound… spot on. But how did it all ride?

Coily goodness

The Ride

To begin with, the spec of this bike has a real influence on how it feels to ride. Basically, it is specced amazingly well, with all the sorts of bits I’d like to see on my own bike. This made for a bike that took me no appreciable getting-used-to period. You can hop aboard the Aeris 9 and dive in. This is all helped by the fact that the rear shock comes supplied with a spring rate that suits your weight, and the set-up ‘cheat sheet’ on the back of the Zeb fork leg is pretty much bang-on to how it should be set up. Finding the rear shock a bit too bouncy up that first climb? Flick the climb switch. Or, if you have few more seconds and know your damping onions, dial on a few clicks of Low Speed Compression. I would caution about quelling the suspension’s suppleness too readily though because that back-end traction can get you up the most ridiculously sketchy and steep technical climbs. As well as increased grip, the suppleness is just that bit less back-jarring. You get far less beaten up over the course of a ride. Yes, I am getting old. On smoother climbs, I must confess to using the climb switch. It comes with the attendant risk of forgetting to disengage it at the top, but it’s nice when you’re ugly-pedalling-tired. And there’s the placebo effect too no doubt that comes with flicking a switch for climbs.

What, no head badge?

When it comes to the sort of riding where you’re going in deeper than the sag point, there is a really nice level of support at the rear. As well as this helping in terms of practicalities, like avoiding pedal strikes, it means the bike responds really enjoyably and usefully to steering inputs and to pumping or working-the-trail for maintaining or increasing your momentum. This isn’t a ‘soft’ ride that absorbs all the kinetic energy coming into a corner and leaves you struggling to get back up to speed upon exit. You are still using the travel on offer though. Geometry-wise, I really like how the numbers work together. There is a flip chip in the chainstays and some riders may prefer the shorter setting (which also has steeper angles). but I am not a nu-skool manualling jibber. I marginally prefer the longer (and slacker) flip-chip setting. My wheels don’t often leave the ground. But they are quite often heading some down something steep and tight. Still, it’s nice to have the flip chip there and, for once, the adjustment is actually significant to the handling.


For something this metal-looking and coily, the Bird Aeris 9 is easy to ride swiftly. It has excellent pace, whether that’s when ascending, descending or traversing. The general stance of the bike is one of stability. But that isn’t a euphemism for ‘boring’. The Bird Aeris 9 is excellently playful when you want, or need it to be. It’s one of those surprising bikes that appears to be ‘aggro’ or ‘overkill’, but actually turns out to be a really pleasant all-round mountain bike. The rear suspension, helped in no small part by the truly excellent Formula coil rear shock, is comprehensively sorted. Supple and hoovery, yet impressively supportive and accurate when it comes to responding to your intentions. The lonnnng geometry numbers may get some prejudiced people rolling their eyes, but the proof is in the trail pudding and the Aeris 9 can put the miles in just as well as it can get the smiles out.

Frame // Aluminium 6066, 160mm
Shock // Formula MOD Coil w/ Lightweight Spring, 230x65mm
Fork // RockShox Zeb Ultimate RC2, 170mm
Wheels // Bird Factory – Hope Pro4 hubs, DT Swiss 29 E532 rims
Front Tyre // Maxxis Minion DHF 29×2.5in 3C MaxxTerra EXO TR
Rear Tyre // Maxxis Minion DHR II 29×2.4in WT 3C MaxxTerra EXO TR
Chainset // SRAM GX Eagle DUB
Drivetrain // SRAM GX Eagle 12-speed, 10–52T
Brakes // Formula Cura 4, 203/180mm
Stem // Bird 35 Stem 40mm
Bars // Big Bird Baw Bar 35, 800mm, 20mm rise
Grips // Race Face Getta Grip Lock-on
Seatpost // Bird Down Dropper V2.1, 200mm
Saddle // Bird Stork
Size tested // M–L (Medium–Long)
Sizes available // Medium, Medium–Long, Large, Extra Large
Head angle // 63.1° / 63.6°
Effective seat angle // 77° / 77.5°
Seat tube length // 420mm
Head tube length // 110mm
Effective top tube // 625mm

Review Info

Brand: Bird
Product: Aeris 9
From: Bird Bikes
Price: £3,990
Tested: by Benji for Singletrack World Magazine Issue 148

Orange Switch 6er. Stif Squatcher. Schwalbe Magic Mary Purple Addix front. Maxxis DHR II 3C MaxxTerra rear. Coil fan. Ebikes are not evil. I have been a writer for nigh on 20 years, a photographer for 25 years and a mountain biker for 30 years. I have written countless magazine and website features and route guides for the UK mountain bike press, most notably for the esteemed and highly regarded Singletrackworld. Although I am a Lancastrian, I freely admit that West Yorkshire is my favourite place to ride. Rarely a week goes by without me riding and exploring the South Pennines.

More posts from Ben

Viewing 4 posts - 1 through 4 (of 4 total)
  • Bird Aeris 9 review
  • hopefiendboy
    Full Member

    What is the weight of the bike you tested? Ta 🙂

    Free Member

    No idea what any of them geometry numbers mean apart from the seatpost. Great to see manufacturers actually putting decent length droppers in new bikes so they actually fit people from the off.
    ( looking at you Trek with your ridiculous 150mm pos on the Slash)

    Free Member

    They have released the AM bike since this article which is a carbon version, with very similar specs.

    I have an aeris 9, I really like it. Built up with a coil, Zebs, ex511s and hope V4s. Light it isn’t, but when you point it down it’s mega

    It does pedal very well, but not what you’d call ‘spritely’. I had a jeffsy before, and getting up and ‘sprinting’ was enjoyable and rewarding, that isn’t the case with the aeris.

    But some of that is likely down to my choice of parts and build spec.

    Free Member

    Which shock are you using Jake?

    I agree about the pedaling manners. I’ve felt a bit overbiked for most of my UK riding, but it really came into its own in the Alps this month.

Viewing 4 posts - 1 through 4 (of 4 total)

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