Muddymoles mountain biking in the Surrey Hills and Mole Valley

Bird Aether 9 review

Posted by Matt | February 6, 2024 | 4 comments so far

Bird Aether 9 with Hutchinson tan wall tyres
I’ve had my Bird Aether 9 since January 2021 and now have over 2,500 miles on the frame.

It’s more than time for a review but TL:DR? I’ve not regretted it for a moment.

First, it’s time for some background.

Why choose the Aether 9?

The short answer is because it’s a modern trail bike with progressive geometry, 130mm of rear travel backed by a manufacturer with a great reputation for customer service.

But there’s more to it than that.

Around the middle of 2020 I think, Bird announced the launch of an alloy Aether 9 29er version of their existing Aether 9C and a sister to the smaller wheeled Aether 7 trail bike. I was immediately interested because at that point I was reaching the end of my enjoyment of my 1st generation YT Jeffsy.

Like most drivers to upgrade, it had become clear I couldn’t keep up with my fellow Moles! And to be fair, the goalposts regarding what a trail bike should be had been shifting dramatically throughout the latter half of the 2010s.

Bird Aether 9 geometry chart

It’s all about the geometry

Longer, lower, slacker.

Who hasn’t heard those three words? Like an easily digested political slogan repeated again and again for the message to sink in, the bike industry had an easy to push message for mountain bikes. And my Jeffsy was the wrong side of it when all the dust had settled.

I already had a taste of the future. I had a Bird Zero AM which I absolutely loved and that fitted me like a glove. It’s only limitation being a lack of rear suspension.

To be clear, I would have at least considered another Jeffsy but even the new one had more conservative geometry to my Zero AM and the price was excessive. Similarly, I felt the Aether 9C was too expensive for me (and to my eyes is not a pretty bike. Plus, I really didn’t like the colour options!).

All this to say that when Bird announced the alloy Aether 9 I was very interested. My plan was to cannibalise the Jeffsy, sell that frame and move what parts I could to a brand new Aether 9 frameset.

The Aether 9 frameset

My time with the Zero AM was the first time – if I’m honest – that I really found a bike that fitted me. Running a M/L frame, it had a 1201mm wheelbase, a reach of 472mm and a 630mm effective top tube. With a 50mm stem it fitted my 5 foot 10 inch (and a bit!) dimensions perfectly.

So the first thing I did was look at the Aether 9 numbers. In size M/L, the Aether 9 has a 1235mm wheelbase, a reach of 484mm and an effective top tube of 630mm. Basically – allowing for the 29 inch wheels – the key dimensions were very, very close to my hardtail, but betterer!

At 65° the head angle was a fraction less slack but then it slackens off when you sit on a full susser. And it had 130mm of rear travel that my hardtail lacked.

Only three things bothered me.

  1. My Pike RCT3 fork had a 51mm offset (Bird ‘recommends’ 42mm)
  2. Was 130mm of travel going to be enough and
  3. I didn’t really like any of the colour options!

Well, that fork offset was a worry. At the time (up to late 2020), offset was a big buzz in bike geometry circles. The argument being that long, low and slack was going so far that you needed a shorter offset to sharpen the steering.

This theory is true. In theory. But after reading some back to back reviews in general and hearing from Dan and co. at Bird it was clear this was a much more nuanced thing. Basically, you can run an Aether 9 with a 51mm offset and you’ll get a slightly more stable and slightly less responsive bike. But most riders won’t really notice.

Well that was good enough for me. Because I didn’t have lots of money to spend a whole chunk on a new fork.

These days, no one really talks about fork offset anyway.

Next, was 130mm enough travel? This was harder for me to resolve. I didn’t really know and at the time I had been riding 140mm or more bikes for over a decade. I reasoned it was only a 10mm shortfall and I still had 140mm up front as well as 29 inch wheels, so it couldn’t be that bad.

And… Bird know what they’re doing. I think the latest downcountry bikes from multiple brands have confirmed they were definitely on to something too.


Finally, the colour! This was very, very nearly game over for me. My three options were:

  1. Raw lacquer (basically unpainted aluminium)
  2. Burgundy Red (Ron Burgundy!)
  3. Or… Tungsten Grey

The Nest (the Bird community) absolutely LOVE the raw finish. With massive respect to them, I do not. Like the Tungsten Grey, it is a tone, not a colour and I really like colour (my Zero AM was bright Atomic Blue).

But I don’t like all colours – for example, I hate red bikes! That basically ruled out all the available options. I tried but… I really don’t like red bikes!

I must have really wanted that Aether 9 frame though. In the end I decided to put up or shut up and went for Tungsten Grey, thinking after a couple of years of hard use I could have it resprayed Atomic Blue (which ironically, Bird now offer for the Aether 9 bike/frameset anyway – karma!).

To mitigate the awful greyness (to my mind) I decided to carefully accent with purple anno and judicious use of a couple of strips of bright lime green vinyl and have never had any regrets since.

Component choices

Having sold the Jeffsy I was left with a smattering of parts. But really, it was time for it all to go. 2×10?? Bin it! A different shock stroke to the Aether? No avoiding buying a new one then. An old Rock Shox Reverb? Nah! So I ended up buying:

I was all-in on purple.

First ride on the Aether 9

All that fiddling and fettling meant I didn’t get the bike out for its first shakedown ride until the last Saturday in March 2021.

Then, on my second ride, I comprehensively crash tested my new bike.

Matt on his backside, no bike to be seen

It was so fast it overtook me! Ha, not really. I hit a ‘hidden’ tree stump and found the Bird really did want to fly.

Reaching full travel on my forks with a BANG! I flipped straight over the bars at speed, ending up sitting on the downslope of a bank. The Bird flew away over my head and didn’t land for another 10 metres, passing a confused Tony in the process.

All I could see was my latest bike investment disappearing down the trail!

It has to be said, it takes quite a lot to go over the bars of a long wheelbase trail bike with a 65° headangle…

From such humble beginings

Miraculously, I was unharmed. Even better, the Aether 9 didn’t have a scratch on it either.

From the start the bike has been exactly what I was hoping. Having refined my appreciation of geometry numbers – mainly Reach and Effective Top Tube length with the Zero AM I was pleased to see my ‘calculations’ worked out pretty much perfectly.

I mentioned earlier the key dimensions versus the Bird Zero AM were close. Actually the combined ETT and stem length in size M/L are identical. In terms of Reach, the figures are 12mm longer for the Aether 9.

Combined with the longer wheelbase of a 29er, the Aether 9 is just slightly more stretched out than the Zero AM but for all intents and purposes it feels like a full sus Zero AM. I can only imagine the Zero 29er feels even better.

Bird Aether 9 at Abinger Roughs

On the trail this translates into two things.

First, the longer wheelbase, bigger wheels and longer Reach means the Aether 9 lopes along very nicely indeed. It has surprised me by being quite the mile muncher and last summer suited it very well running a ‘fast’ Hutchinson Kraken on the rear. On dry ground it belts along, which was an experience I never really got from the YT Jeffsy. You were always ‘on’ the Jeffsy whereas with the Aether 9 you are ‘in’ it.

Give it a big day out and it will quietly get on with covering ground; I have half-baked ideas of the South Downs Way in a Day again this year and the Aether 9 will be perfect. It winches uphill at a decent lick helped by the steepish seat angle.

Going down

There is a flipside to that, something that is an inevitable result of modern geometry.

When the trail points downhill, or when it gets twisty, you can’t sit back like you are riding a sofa. You will understeer straight off into the scenary. This is in no way a criticism of the Bird either; it does just exactly what you’d expect if you stop and think for a moment.

With modern bikes, the front wheel is some way ahead of you. Long, Low and Slack remember?

This makes modern bikes very stable but potentially slower to turn. Add in a longer fork offset like I have and the key to getting the best out of the Aether 9 downhill is to drop the saddle, shift your hips a smidge forward and put some load into the front of the bike.

Do that and it rips. With a suitable front tyre – I’ve used the classic Maxxis Minion DHF MaxxTerra 2.5 and recently (again in the dry summer) a Hutchinson Wyrm 2.4 – if you get the front end to stick then the rest will follow.

The Aether 9 can be made – without much effort but a certain technique – to change direction with alacrity. I’m sure you can also push those characteristics forward with a modern fork offset and and a shorter stem. I absolutely love how secure and predictable its handling is and it performs at levels far beyond what I’d expect a 130mm bike to do.

Just give it some ‘body English’.

I used to think the optimal bike round the Surrey Hills (assuming you weren’t going nuts) was my On-One Inbred which had just 100mm of fork travel. It was supple and flowy and you could get away with a lot.

The Bird Aether 9 is not like the Inbred of course. But shorter travel and a responsive bike has a lot going for it.

Stick the Aether 9 down Barry Knows Best, or rip down Petrol Pump (or Pink Sock, or, or – the list is long) and it is an absolute joy. You can transition from mile munching to trail shredding in short order.

Matt at Tadworth golf course

Any downsides?

I’ve stacked the Aether 9 hard more than once. Apart from my first ride shenanigans, I wiped out at speed on some berms at Bike Park Wales, enough to concuss myself for the first time. And last year, I barrel rolled the bike over a log jump on Sauvage. On both occasions I consider myself lucky not to have really hurt myself although both hurt plenty at the time.

It’s hard to ignore that these incidents happened on the Bird. Honestly that thing likes to fly!

Thinking more carefully I blame it on a couple of things. First, on both occasions I was running a ‘fast’ rear tyre – a Maxis Ardent at BPW and a Hutchinson Kraken on Sauvage. That thing I said about making the front stick and the rest will follow? Well you could say I was asking for it.

But I don’t think that’s quite true.

I think I have a spec issue on my Bird, one that is my own fault. Yes those tyres are fast. But the Bird uses a classic Horst linkage design that makes it incredibly supple out of the box. It also means it will always want to move through its travel at the slightest provocation. There’s not a lot of platform built in.

All this is perfectly fine except in my wisdom I chose to run the entry level Rock Shox Deluxe Select RT as a rear shock. Together with the Horst link suspension, if you want to run the shock to get a supple bike it doesn’t take a lot to blow through the travel or catch a pedal. Both my accidents were – at least in part – from the suspension bottoming out and on Sauvage my pedal dug in.

Most of the time the Rock Shox shock is good enough, but when you are putting demands on the bike I think you really need something better. I have my eye on a Cane Creek DB IL II but I know a LOT of the Nest like to run coil shocks at the slightest provocation! In either case, its possible to get a good supple feel (which suits the bike’s characteristics well) with more platform for those moments when you really need it.

Race Face Next 35 on Bird Aether 9

In summary

If the Bird Aether 9 is in your sights – based on capability or on price – I don’t think you will be disappointed. It will compliment your riding all day long but has enough core strengths to step up to the mark when you ask.

My view is not to skimp on the shock; go for the best you can afford. I don’t think it has to be a coil although that seems to be de rigeur. Just something with a broad spread of capabilities and the ability to tune the high speed compresison so you don’t blow through the travel too quickly.

As for robustness, well my frame has been through a lot and it is unmarked. I spent time home-styling an invisiframe style effort but it’s probably worth getting the real thing. It has paid off with a bike that’s still looking fresh after 2,500 miles. Next up, a full bearing replacement.

There are no doubt better bikes out there but they are significantly more expensive for not a great deal extra. The Bird is reliable, completely serviceable from home and comes with the support of Dan and co. at Bird HQ which differentiates the brand from others on the market. It’s long and slinky and I even like the purple and grey combo!

(But don’t forget it now comes in Atomic Blue…)

You’d never say a Mole and a Bird would get along but it turns out they do. I have no plans to swap anytime soon.

Filed under Bikes, Reviews in February 2024


About the author

Matt is one of the founding Molefathers of the Muddymoles, and is the designer and main administrator of the website.

Having ridden a 2007 Orange Five for many years then a 2016 YT Industries Jeffsy 29er, he now rocks a Bird Aether 9 and a Pace RC-627.

An early On-One Inbred still lurks in the back of the stable as a reminder of how things have moved on. You can even find him on road bikes - currently a 2019 Cannondale Topstone 105 SE, a much-used 2011 Specialized Secteur and very niche belt drive Trek District 1.

If you've ever wondered how we got into mountain biking and how the MuddyMoles started, well wonder no more.

There are 4 comments on ‘Bird Aether 9 review’

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  1. Elliot says:

    Those purple details really perked up the look of that bike

    I suspect there’s little mention of fork offset now because outside of Cannondale (using even longer 55mm for the Lefty) almost every mainstream brand has settled on speccing short offset.

    Shorter offset makes steering feel slower. Wants to go in a straight line and resist flopping from side to side. It’s not a big deal, but does feel like I’m making a lot less steering corrections. Just point the bike and shoot.

    Definitely get a new shock on there. Think I had the same Deluxe come on my Whyte S150 and it was diabolical. Pedalled like a sponge and was spiking / overheating just riding over rocks at Afan. Installing a Cane Creek completely transformed the ride. Actually had a DVO Topaz on there in the meantime because the Deluxe broke right before a trip, I panicked and ordered 2 shocks and took the one that came quickest. DVO was excellent too, with it’s own unique feel, but prefer the Cane Creek pedalling platform.

    • Matt says:

      Hmmm I definitely understood the longer offset made things more stable and generally slower.

      You are saying only up to a certain point when the steering flops but shorter makes it all more consistent.

      I’d be interested to try that, sooner or later I will upgrade and find out for myself!

      But after the bearing replacement, the shock definitely comes first.

      The Deluxe is exactly as you describe, pattery and overworked on trail chatter unless you run it soft or slow, then goes straight through it’s travel when pushed.

      Having tried Lloyd’s Santa Cruz with a Cane Creek, I took off on a jump on Rumble* and was in the air so long I thought you’d be picking me out of a tree! So I feel the DB Air II is probably a really good match for the Bird.

      It’s all relative – the Aether rides and handles really well. But sounds like there’s more to unlock from both ends of the bike. Which is a nice thought.

      *BTW, rode Rumble last night and there’s a new log jump near the top.

      I didn’t have time to stop so launched it on the Pace hardtail, it is fine but needs some momentum to help you over. I spent the rest of the run wondering what else was going to surprise me, not the nicest feeling.

      • Elliot says:

        51 was originally cooked up by Gary Fisher so they could get 29ers to steer quicker like 26 while slackening the head angle. Before that designers were trying to achieve similar using super steep angles like Dave’s 73 degree Intense Spider 😱. At the time a Gary Fisher Paragon with 69 degrees felt pretty slack by comparison. Added stability of 51 is less a function of how the offset works and more to do with a few mm extra front-centre/wheelbase and combining with a slacker angle.

        Less offset = more trail = improved steering stability. I always think the supermarket trolley example is a good one. The wheels used to shake on old trolleys because there wasn’t enough trail. Newer ones with increased trail the wheels follow where the trolley is pushed.

  2. Robert Scott says:

    I’ve got one in atomic blue

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