Muddymoles mountain biking in the Surrey Hills and Mole Valley

I might have bought a new bike… well a frame at least…

Posted by Matt | January 22, 2021 | 12 comments so far

Bird Bike Aether 9
I’ve been turning this over for a while in various permutations and have finally decided now is the time to sell the Jeffsy.

The YT Jeffsy is a lovely bike, and being a mail order bike from Germany – albeit with a new YT showroom now in Guildford – it has been quite a novelty to run something that not many people have. Despite that, I think it’s a good time to sell because I fancy a change. My experiences with the fit of the Bird Zero AM have also shown that the Jeffsy doesn’t quite fit the way I would like.

So what have I bought? A glance at the photo at the top of this post will tell you, I’ve bought a Bird Aether 9 frame in Tungsten Grey, size ML.


A glance at the numbers tells you why.

A 65° head angle with a 77° seat angle for start, and a reach that’s just 12mm longer than my Bird hardtail. With a 50mm stem I’ll have the same ‘ETT + stem’ dimension as the Zero and a slightly longer reach. In contrast, that same ‘ETT + stem’ dimension on the Jeffsy is 15mm shorter even with a 60mm stem, and the reach is 39mm shorter. Basically both Birds are roomier beasts.

Other comparisons, this time with Mark’s Aeris 145 are also interesting. The Aeris 145 has a wheelbase of 1230mm on 27.5″ wheels; the Aether has 1240mm on 29″ wheels with less rear travel helping to square the equation. The Aether 9 has a whole 62mm extra in the wheelbase over the Jeffsy!

Given the above and given my experience with the Zero I know the geometry just seems to suit me, so the bike should fit me well. I feel confident it will climb well and going back down should be a hoot. I suppose ultimately these differences come down to personal taste because the Jeffsy has always been a nice place to be. Maybe my taste has changed?


This whole exercise is not without cost though and I still have further expense to make.

The drivetrain on the Jeffsy is 2×10 and the chain and chainring are wearing out, which was another one of the prompts to change the whole bike.

The Aether won’t take a double and actually, I’ve got on really well – better – with the 1×11 (30T with a 10-42 range at the back) set-up on the Zero. So, this time round I think I shall try and get hold of a Shimano Deore 1×12 drivetrain. That’s likely to be what holds up getting the new frame to the trail and I still have to decide if I buy new Deore brakes and sell the SLX M785 brakes I have, or keep those.

I also have a small doubt over my Pike RCT3 fork. It has a 51mm offset, the frame was designed around a 42mm offset and given my over-analysis of the geometry above, this is a concern.

I don’t think I’ll notice really and if I understand it correctly the effect of the longer offset is to sharpen the steering(?). Or vice versa(!?). I suspect there’s a lot of marketing spin on it to sell more bikes, but it’s not beyond the bounds of reason that I’m wrong and all things being equal I would buy a new fork. Time will tell.

Other costs are aesthetic. I really don’t like black bikes (another reason for selling the Jeffsy, although it does have blue accents). I don’t expect Tungsten Grey to be much better so I will have to sprinkle the new frame with some judicious anodising. The jury is out until I have the frame in my hands and can see the actual shade of grey, I could go purple or maybe lime green.


In fact, Bird’s colour options for the Aether 9 very nearly put me off the bike entirely.

I am convinced that whoever currently chooses the Bird bike colours may well be colour blind, since the available colours – Raw aluminium with lacquer, Tungsten Grey or the humourously named Ron Burgundy – all end up being little more than tones to a person with red/green colour blindness. I could be doing them a dis-service; the Nest (Bird’s owner-community) absolutely love the Raw lacquer and it was the first to sell out (there are more coming).

To be fair to Bird, their muted colours seem to have coincided with increased sales from what I can see. Had the Aether 9 been Lime Green or the Atomic Blue of my hardtail I would have been buying it without hesitation. Or copper perhaps; maybe even pistacchio?! Hmmm (rubs chin).

At this point I reserve the right to get a respray in the future and Bird seem quite happy to provide the artwork for frame decals, so…

This all leaves me as a two-Bird owner. I’m happy with that for the time being but it opens up the option later in the year for a switch to some other 27.5″ frame for my hardtail. I really would like something in steel but given current availability and my now impoverished bank account, it will have to wait. I very nearly went for the Pace Cycles 627 recently but they sold out very quickly.

Worth mentioning though that Bird have an 853 hardtail arriving in March/April albeit in 29″ form to start with. You can also look forward to a stainless steel option using KVA MS3 stainless steel if you fancy something quite outre.

Filed under Mutterings in January 2021


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 12 comments on ‘I might have bought a new bike… well a frame at least…’

We love to get comments from our readers - if you've spent a few moments to comment, thank-you.

If you haven't had a chance yet, jump to our comments form if you have something to say.

  1. Lloyd says:

    Matt I fully support the comment that as the chain and chainring were worn out I decided the change the bike. Perfectly sensible and appropriate!

  2. Tony Gordon says:

    Top man maths there Matt. New drivetrain = new frame!

    The Bird looks good (do you now own a “flock” now). I’m sure it will ride really well given those geometry numbers. However I think that you have mentioned what may be your biggest upcoming issue – finding a 1×12 groupset!

    I love the idea of a stainless steel hardtail. I’ve always fancied a 953 steel road frame but not many frame builders like to build in stainless since it’s so hard to work/cut

  3. Matt says:

    It’s not that the drivetrain has completely given up but it is wearing out, and do I want to keep buying 2×10 bits which would then ‘commit’ me to using them until they wear out? At that rate I’d never buy a new bike and what sort of thinking is that?

    I could have put a 1×12 on the Jeffsy as most Jeffsy’s are 1x anyway but my base spec came with 2x to keep the cost down. Again, when would I ever buy a new frame??

    The decider was the geometry of the Bird hardtail I’ve got. I just love the fit and handling and figure a full sus version of that will be spot on.

    But yes, getting hold of Deore 1×12 at this point is going to hold me up I’m sure…

  4. Terry says:

    Ribble do a steel or Ti frame in 650/27.5. Pretty slack. ?

    • Matt says:

      I agree Terry, I’ve had the Ribble HT 725 on my radar too. Looks nice, and a sensible price. Size-wise, the 18″ would give similar numbers to the Bird with a 35mm stem, with a slightly slacker seat angle.

      The difficulty – same as the Pace and the Bird – is actually demo-ing these things, even in non-pando times. I want a bit of steel twang rather than a super stiff frame (as long as the front is strong so it steers OK I don’t mind the back end flexing) but the Ribble looks a little chunky round the BB.

      Hard to tell because there’s not many reviews. You’d think with so many hardtails on the market these days they would get plenty of coverage, because the demand must be there but a decent review is pretty rare.

  5. Jez says:

    Matt, love the grey frame!!
    Geometry looks very up to date, should be a good bike all round.

  6. Elliot says:

    Looks like a good bike!

    Wouldn’t bother changing a fork just for a reduced offset. Going between both it’s noticeable but if you’ve not ridden both you’re not missing much. Shorter offset wants to go in a straight line more, like a shopping trolley wheel follows where trolley is pointed. Less steering adjustments mid corner. Might give marginally more grip as well. Longer offset makes steering quicker or more twitchy. Having the wheel further out in front could be beneficial for really steep riding.

    • Matt says:

      Thanks for the explainer Elliot. I am sure the 51mm offset will be OK for the time being. Having a more manouvreable bike is no bad thing with a long wheelbase bike and I’m sure its a question of degree rather than fundamental differences.

      Bird actually say the AM9 can be used with 37 to 51mm offset, take your pick. So the Aether should be OK, largely being a short travel AM9.

      And I plan to run a 50mm stem rather than a 35mm which slows the steering a touch.

      Any thoughts on my SLX M675 brakes? Should be OK or would the Deore M6100s be better (2-pot version, not 4-pot)? I mean the M675s stop me on the Jeffsy as it is…

      • Elliot says:

        Think M675 was the last generation before leaking piston and moving bite point issues came along, which they still haven’t fixed. Main innovation with M6100 seems to be the extra lever brace for stiffness. It works, but only because the previous lever had narrow clamps that flexed. Your older SLX levers have a wider clamp that was fine. 4-pots are worth considering as the modulation is quite a lot better, not just power.

        Are those your brakes that vibrate? Could always treat them to new pads and rotors.

  7. Tony says:

    The Pace has Hope floating rotors and ice tech Shimano pads. Works really work.

    Green accents I think!

Leave a comment…

Have your say – we'd love to hear what you think.

If you have something to add, just complete this comment form (we will not publish your email address).

*Required information.

This site uses Akismet to reduce spam. Learn how your comment data is processed.