[Closed] Size Bird AM9 for a 5'11" 181 guy

Ask on the Bird Facebook page and / or the Aeris thread on pink bike if you don't get an answer. FWIW I'm pretty much same size as you and have an ML 120 which is 5mm shorter reach than the ML am9. I suspect you'd fit either size but if you haven't spoken to someone at Bird then give them a call or wait for @benpinnick to respond 🙂

Whereabouts are you that means you can't try one? Worth asking Bird if they know anyone on the owner's group near you who might have one you can sling a leg over?

FWIW I'm a hair under 6' with a positive ape index on a L Aeris 145 and it's great. That said, I could ride an ML fine, and even my other half's Small Zero AM doesn't feel that small! Sorry, that doesn't help, does it?

5ft 11in is bang on the line between sizes, so either will be fine - base your choice on the type of riding you'll do and/or choose to help strengthen your weaknesses.

The smaller bike will be more playful and manoeuvrable, easier to wheelie/manual, better on tight and twisty trails, and flat trails.

The longer bike will be better downhill, at speed, more stable, better on the steep and/or techy stuff.

I'm not so good on the steep techy gnar so will be going long on my next bike.

Also make sure you can fit a 150mm dropper, or maybe you want a 170mm dropper? seat tube length will also dictate what size.

I’ll be metric for ease - I’m 179cm tall, have a 188cm armspan and 85cm inseam. I have an older Zero AM medium, a Spitfire large and Levo large. All three are 455mm reach (the hardtail sagged, the other two static).

I prefer the steering feel from 50mm stems (I’ve tried 35mm and it was too quick/nervy) and fairly wide (750-770mm) bars (they’re limited by our tight local trails). I have 185mm droppers posts on all of them.

“The longer bike will be better downhill, at speed, more stable, better on the steep and/or techy stuff.”

This is not true. The longer bike will be better on fast open stuff due to the increased stability. Steep and/or tech stuff is not always easier on longer bikes because you end up running out of arm/torso length to keep your weight centred over the BB as the gradient gets steeper - that’s why WC DH bikes have not gone so massively long in reach (though they are long once you measure the reach with the bike angled for a steep descent).

Short bikes are worse on steep stuff because you have to move your weight so far back to keep the bike balanced - but we’re not comparing short and long, we’re comparing long and very long (for your height).

The longer your legs vs your height, the less reach you’ll need because your torso will be relatively shorter and your femurs longer - this will naturally place your hips and thus your centre of mass further back when in the attack position. If you size up to a large you’ll have to move forwards to weight the front wheel, rather than staying centred.

Most people don’t realise this - they think long arms will require a longer bike than someone of the same height with short arms, but long arms usually go with long legs (and thus shorter backs). Longer arms often benefit from wider bars - but don’t go too wide for the trees where you ride!

I have already written to Bird. They say I can choose either and just choose a 50 or 35 mm stem and that the L will be better for decent focused riding and M/L for general riding. I do both... People seem happy both sizing up and down, maybe because they made a more thought after choice than me in the first place? Coming from a size M Codeine everything new is just different, that bike was recommended up to 183 cm height and has a reach of 412 mm. It still feels OK, even though I've done a couple of OTBs.

I've also been thinking about why weekend warriors on Enduro bikes need such a long reach while WC down hill racers don't? The EWC racers, how do they size their bikes?

I ride flat pedals if that matters.

I'll be running a 170 mm OneUp dropper if that matters, so I'll be hiding 210 mm of post in the L frame and 180 mm in the M.

I use flat pedals if that matters.

I’m 5’9 on an ML Aeris 145 but I find it quite long and really have to work hard to weight the front wheel. I have a 32” leg and quite short arms though and quite a short torso.

I was hovering over the M and ML - no way I’d consider the large. I’m sure Ian PV on here is a couple of inches taller than me and rides an ML AM9.

“The EWC racers, how do they size their bikes?”

Sam Hill (5’10) is on a medium Nukeproof Mega (435mm reach). Richie Rude (5’11) is on medium Yeti SB150 (460mm reach).

In WC DH Aaron Gwin (5’10) rides an XL Intense for racing because it’s faster but says he prefers riding the Large. Large is 450mm reach, XL 480mm.

Also, flats generally require a slightly more rewards body position and thus a shorter reach bike.

I’m just under 180cm and ride an m/l. Fit is great for both fast and slower steep/tech trails. Climbing is fine too. I love the bike but I’m glad it is not my only one - I don’t like riding it on flat trails very much.

that’s why WC DH bikes have not gone so massively long in reach (though they are long once you measure the reach with the bike angled for a steep descent).

Are you talking the Pro bikes or regular DH bikes anyone can buy? Pro bikes, well those riders are not like any of us mere mortals so the normal rules don't apply 😀

Just checked the YT Tues and Santa Cruz v10 and in my size they have a 505mm and 492mm reach respectively, vs the Jeffsy trail bike at 510mm reach, and generally anything around 500mm is classed as 'long' for me.

Also I agree that 500mm reach at 5ft 11 is very long, it's long for me at 6ft 3!!

Flat trails, do you mean flat as in mostly seated cross country rides or flat as really rocky and technical mostly standing up going full throttle? Or both?

Seems no other bike brand recommended a reach of 500 mm for a 5'11 rider? I guess Bird has a reason for their recommendations. I usually just buy by the makers recommendations, maybe it's wrong in this case.

At 6'3 you should go for the XL by Birds size table, 522 mm reach, recommended from 6'2 and up

You can't look at reach really in isolation as a number to go by, because it's one of many numbers that make up the bike. 500mm on it's own is big, but if it's got a super steep SA, the ETT won't be that much different to a more contemporary bike, but you will be in a different position on top of it (more forward, with more weight on your hands).

Personally as a fun, do everything bike, I would be picking the M/L and i'm taller than you. I'm fortunate enough to have a shorter travel bike which takes up 90% of my riding, which is similar in numbers & it's great. I also have a massive thing which is more akin to the L size (but with a slacker HA & longer CS), it's a real monster truck but it needs the space & speed to work properly.

If I could only have one bike, it wouldn't be the bigger one.

Yes, the reach is more for standing up.
My old Codeine is a bit short seated. Felt horrible with 45 mm stem, that is definitely to short for me. My Canyon Dude fatbike size L is long-ish but OK seated. I tend to sit on the tip of the saddle on both, don't know why.

Codeine ETT 600 + Stem 60 = 660
Dude ETT 642 + Stem 45 = 687
Bird L ETT 655 + Stem 35 = 690
Bird M/L ETT 630 + Stem 50 = 680

"I have already written to Bird. They say I can choose either and just choose a 50 or 35 mm stem and that the L will be better for decent focused riding and M/L for general riding."

I don't think that's very clear info from them - what they should have said is that the L will be better for enduro racing and the ML better for general riding. No-one buying an AM9 is riding without a focus on the descents - it's a 150mm travel full-sus 29er!

Also, their size guide is confused because the metric heights don't match the imperial heights.

Now I've called Bird and had a chat with Ben. I don't buy bikes often so I don't have much comparison, but their service is excellent, really!

Anyway, since I'm going to replace the Codeine, using the bike for all types of riding (n-1 in the garage selling my Voltage) AND have a bit longer legs Bird suggested to go M/L. Apparently most people between sizes tend to go down on the AM9 (up on the 27.5 Birds). In my size L is for bombing down. I like bombing and carving but not only that. I want a bike to use for everything, especially when traveling. Fun is more important than fast, I'm not that fast anyway, but I sure like to have fun.

475 mm reach for 5'11 seems to be industry standard. Most brands seem to recommend that. The EWS post above is convincing.

Thank you all for your input! I'll definitely be sleeping better tonight than last night.

One can't look at reach in isolation.
Front center is a very important, usually overlooked dimension.
Many of those WC DH bikes will have comparable front centers to a longer reach trail bike. Add a slightly longer stem to match the fork offset and things get really similar

I'd get a test ride - the AM9 is a load of fun, but for me that fun comes from it being fast and incredibly secure feeling.

I'm not sold on it as an all purpose trail bike for me, it takes too much effort to get it going for that - I've got a medium T129 (a great bike but not a bike that is considered particularly agile) and it is lot more lively than the AM9, gets down anything, and is definitely the bike I'd keep if I could only have one bike and wasn't doing DH tracks and uplifts every weekend.

If I was doing uplifts and DH tracks all the time and had to pedal up, the AM9 would be spot on - it bike that climbs ok and descends brilliantly.

Of course, YMMV etc. but I wouldn't want a 150mm 29er as my main trail bike, as a lot of my local trails are flat and reward a bike that pedals better and picks up speed without gravity.

I'm 6ft and wear 33 inch leg trousers, I have a large AM9, it's a big change from my last bike (2010 Gary fisher Roscoe).

I'm very happy with it, I wish I gone for a slightly bigger dropper post, the 125 is not quite enough.

You'll be happy, what colour did you get?

I have a 145, I had 6 test rides to choose between the ML and the L - ended up getting the L. I could have easily ridden either, but I figured if I were going to get a long bike, I might as well make sure it's long! Overall very happy with the bike, but get the piggy back shock, made the back end much better.

The AM9 is slightly shorter than the 145, so I'd go large if I were you. I am 182.5cm tall with a 33.5 inch inside leg. I have the shorter stem option and the longest drop on the bike yoke (180mm?) - the bike yoke is a must have.

I'm 6'1 and demo'd a size L AM9. I ride mostly DH and it felt borderline too big for that, but the length felt amazing for climbing (which I care about less).

Ended up with an XL Capra 29 (485mm reach) and a 35mm stem. Spot on.

Go with the ML

I was in a similar position when ordering a Zero 29. I asked myself what would Geex do?
#bemoregeex

My mate is about 5-10/5-11 and rides a M/L with 35 mm stem and he rates it highly
I’m on a medium 140 Aeris and had a shot on his and it felt really good
Not that much bigger in reach to my bike but was way quicker

Is there a reason why you can't demo? They are pretty good for that.
fwiw I'm 6 foot on a large 145, as someone else mentioned, downhill and being silly they are fab, pedalling flat stuff is hard work. (road work is really awful, not really what it is for but it happens)
I assume the AM9 is similar , I'd demo ride them all, 145, am9 etc

I'm 6ft with 32" leg and have had my newly built up Large AM9 complete for a month. It feels absolutely dialled and I'm glad I went for the L (35mm stem). The numbers (500mm reach) sound big but it doesn't feel big. In fact I'm concluding that I have been riding bikes slightly too small for me for the last 27 years... I can't say I have found mine a beast to pedal on the flat and it goes uphill better than my Liteville 301 - although that does have offset bushes and a -1.5 deg slackset. As everyone else says, demo if you can - I'm near Exeter if that's any help.