Bird Aeris AM9 GX custom review£3,334.00

Bird’s first big wheeler isn’t afraid of big speeds

BikeRadar score4.5/5

While Bird might not be the biggest or boldest brand out there, its bikes certainly stand out. And that’s for good reason. It's been bold with its geometry numbers and its malleable direct buying model allows you to chop and change parts to your heart's (and wallet's) content. The Aeris is Bird's first foray into the world of long travel 29ers and it's done one hell of a job.

  • The Bird Aeris AM9 GX custom is one of our Bike of the Year bikes for 2018. To read reviews of the other contenders and the categories tested across road, mountain and women's bikes, visit our Bike of the Year hub.

Bird Aeris AM9 GX custom frame

I had to run the RockShox Super Deluxe RCT shock's rebound adjuster fully open to get the back end returning as quickly as I wanted
I had to run the RockShox Super Deluxe RCT shock's rebound adjuster fully open to get the back end returning as quickly as I wanted

The AM9 offers up 150mm / 5.9in of rear wheel travel, delivered using a four-bar linkage design all controlled via a RockShox Super Deluxe RCT, which comes without any volume spacers inside as standard.

When it comes to the geometry, Bird has definitely pushed things a little further than most. The AM9 comes in four different sizes, including the medium-long you see here.

The medium, the smallest frame on offer, sports a longer-than-normal 452mm reach, though this isn’t exactly crazy. If you normally ride a medium but want something a little lengthier, chances are you’ll fit nicely on the medium-long, just as I did at 5ft 8in.

This has a reach of 475mm, though the seat tube stands at just 440mm, so there’s even scope to fit a longer travel dropper post should you wish. For the really tall guys and gals out there, there’s also a size large and extra-large which boast reach measurements of 500mm and a whopping 522mm respectively.

Cables are routed externally which is a blessing when it comes to working on the AM9, even if it doesn't look quite as tidy as its internally routed counterparts
Cables are routed externally which is a blessing when it comes to working on the AM9, even if it doesn't look quite as tidy as its internally routed counterparts

A steep seat tube angle of 76 degrees helps to keep things more efficient when climbing, while the 65-degree head angle and lengthy 1,240mm wheelbase add stability when the pace picks up.

Cables are all routed externally to keep working on the bike that bit easier and the British brand has opted for a threaded rather than press-fit bottom bracket, which many will appreciate.

Chunky welds and gussets give the AM9 a reassuringly solid industrial look.

Bird Aeris AM9 GX custom kit

We're big fans of the RockShox Lyrik RCT3 fork. It's impressively sensitive though well-supported when it matters and tuning the end stroke is a doddle
We're big fans of the RockShox Lyrik RCT3 fork. It's impressively sensitive though well-supported when it matters and tuning the end stroke is a doddle

While Bird is a direct buy brand, you can still visit both its northern or southern HQs in the UK to talk to the team and check out the bikes in person. It also has a number of permanent demo fleets dotted about the UK. Still, its business model means that while you don’t get quite the same back-up support as you would when buying from your local bike shop, you do get a lot of bang for your buck.

Where Bird differs here slightly is that pretty much every part on its bikes can be swapped or altered to suit your needs and budget. My bike essentially started out as the GX build, but I customised it in areas I felt were important without going crazy with the cash. That’s why this bike sports quality dampers in the shape of the RockShox Lyrik RCT3 fork and Super Deluxe RCT rear shock, SRAM’s powerful Guide RE brakes and I switched the tyres around a little to suit the rather damp British conditions. This left me with a Maxxis Shorty up front and a High Roller II at the rear.

SRAM's 1x12 GX Eagle transmission delivers a massive gear range which is certainly a real plus on big days out in the hills
SRAM's 1x12 GX Eagle transmission delivers a massive gear range which is certainly a real plus on big days out in the hills

While it’s the geometry that helps the AM9 feel so easy going on the climbs, the wide range GX Eagle gearing from SRAM certainly helps when you start to flag on big days out.

While the Race Face Aeffect 150mm dropper post worked well-enough, it doesn’t feel quite as slick as Fox’s Transfer or RockShox’s Reverb posts.

The Guide RE brakes from SRAM offer loads of easy to control power and felt consistent throughout testing
The Guide RE brakes from SRAM offer loads of easy to control power and felt consistent throughout testing

Bird Aeris AM9 GX custom ride impressions

In terms of set up, the AM9 feels incredibly well balanced from the get-go. It’s very much a case of setting the sag and rebound damping then hitting the trail. That said, in order to get the back end of the AM9 feeling as I wanted, it did mean leaving the rebound adjuster fully open, so lighter riders might struggle getting the feel just right.

On the hill it doesn’t take long to notice how supple and well-controlled both the fork and shock are as you start tackling more engaging sections of trail. This means plenty of traction when you most need it, but no shortage of support when you want to work the bike through undulations or load it hard in turns, leaving you to fly out at speed.

I must admit that I was a little dubious as to how the long reach and lengthy wheelbase would translate on the trail. Thankfully, any worries that the AM9 might feel a little dull or less fun due to all of that inherent stability were quickly put to rest. That’s because the AM9 feels energetic and lively no matter what the gradient or speed might be.

MBUK's Ed Thomsett drifts one of San Remo's many loose, dusty turns on the AM9
MBUK's Ed Thomsett drifts one of San Remo's many loose, dusty turns on the AM9

Lofting the front wheel up and over obstacles is easy and the responsive handling makes chucking it around the trail and playing on jumps a smile-enducing fun fest. It’s seriously fast as well though, thanks in part to that well-centred riding position from which you can really attack the trail ahead. Speed comes easy too and momentum is preserved with very little effort.

It's no slouch in the turns either and although not as calm through the bar as the likes of Whyte’s S-150 on really high-speed, chattery turns, still carves a mean line at pace — I’d certainly be intrigued to try the AM9 with a fork with shorter offset just as Whyte spec.

In fact, I may have over indulged a little through the corners, loosening many of the spokes off in the rear wheel after a good few days in the hills and leaving it feeling a touch flexy when really pushing the bike hard.

I also developed a creak around the bottom bracket area after a few days pummelling the AM9 out in San Remo, Italy, though it was already in need of some TLC before we left the country so it was no huge surprise.

Climbing on the AM9 is surprisingly easy going too. The steep seat tube angle helps to position you over the bottom bracket for more efficient pedalling and combined with the the relatively long 440mm chainstays, which help to support your weight, there’s no front wheel lift when tackling steep pitches.

Overall, the AM9 offers a seriously well-rounded ride. It goes uphill without fuss and feels incredible on the downs, balancing stability and confidence on faster trails well with its nimble, responsive handling which keeps it fun on every trail I rode.

Rob Weaver

Technical Editor-in-Chief, UK
Rob started riding mountain bikes seriously in 1993 racing cross-country, though he quickly moved to downhill where he competed all over the world. He now spends most of his time riding trail bikes up and down hills. Occasionally he'll jump into an enduro race.
  • Age: 34
  • Height: 172cm / 5'8"
  • Weight: 68kg / 150lb
  • Discipline: Mountain
  • Preferred Terrain: Natural trails where the loam fills my shoes on each and every turn
  • Beer of Choice: Guinness

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