Bird Aeris owners thread

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Posted: Jan 21, 2020 at 11:13 Quote
R-M-R wrote:
The colours of the letters correspond to the dials on your shock. ML sequence should be red, then blue, meaning Medium rebound and Low compression. This should be fine for the AM9, if you can get the rebound fast enough.

You could probably reduce your spring rate. I'm heavier than you and I run a 350 lb/in spring, though I do have an additional position-sensitive damper. The AM9 works well with considerable sag.

Ahh cool, there's no coloured sticker like on the air shocks, just the multi digit product code, and ML etched up near the eyelet

I checked with Dan and he recommended a 375 spring

How heavy are you?

Posted: Jan 21, 2020 at 11:16 Quote
rideeverything wrote:
I checked with Dan and he recommended a 375 spring

How heavy are you?

About 78 kg. Add a bit for riding gear and water. I travel light, so maybe 1 - 2 kg less gear than others.

Keep in mind I'm using an EXT Arma with a fair bit of hydraulic bottom-out and more than typical sag.

Posted: Jan 21, 2020 at 12:29 Quote
R-M-R wrote:

About 78 kg. Add a bit for riding gear and water. I travel light, so maybe 1 - 2 kg less gear than others.

Keep in mind I'm using an EXT Arma with a fair bit of hydraulic bottom-out and more than typical sag.
I'm probably 71-72 kg ready to ride and at about ~27% sag at the shock
I'm tempted to pick up a 300 spring since they're only £20. I just don't want to be smashing into the bump stop

Posted: Jan 21, 2020 at 12:47 Quote
27% is really low for a highly progressive motion ratio. Might as well try the 300 lb/in spring at that price; either it'll be the best £20 you could spend on your bike or, if it's too soft, at least you'll know the ideal rate is 325 lb/in.

Posted: Jan 21, 2020 at 13:40 Quote
R-M-R wrote:
27% is really low for a highly progressive motion ratio. Might as well try the 300 lb/in spring at that price; either it'll be the best £20 you could spend on your bike or, if it's too soft, at least you'll know the ideal rate is 325 lb/in.
For sure cheaper than a service and revalve!

Posted: Jan 21, 2020 at 13:48 Quote
rideeverything wrote:
R-M-R wrote:
27% is really low for a highly progressive motion ratio. Might as well try the 300 lb/in spring at that price; either it'll be the best £20 you could spend on your bike or, if it's too soft, at least you'll know the ideal rate is 325 lb/in.
For sure cheaper than a service and revalve!

Exactly. You can even sell the spring, maybe without taking a penny of loss.

The lower spring rate will require less rebound damping. This may become a bigger issue than anything to do with the compression damping. Even if you can really open up the low-speed rebound, via the adjuster wheel, the bike may feel like it doesn't recover sufficiently quickly from big impacts due to the inability to adjust the high-speed rebound.

Posted: Jan 21, 2020 at 14:12 Quote
R-M-R wrote:

Exactly. You can even sell the spring, maybe without taking a penny of loss.

The lower spring rate will require less rebound damping. This may become a bigger issue than anything to do with the compression damping. Even if you can really open up the low-speed rebound, via the adjuster wheel, the bike may feel like it doesn't recover sufficiently quickly from big impacts due to the inability to adjust the high-speed rebound.

Currently I'm running the LSC completely open, and I think 5 or 6 clicks in from full open on LSR

Going to a softer spring I'll be able to wind on a bit of compression if need be, and have clicks to spare on rebound too

Posted: Jan 21, 2020 at 14:38 Quote
Sounds like you ought to be good to go, then.

Posted: Jan 22, 2020 at 1:57 Quote
Hello! Ive been looki g at the new propain tyee 29. Looks really nice, i wish Bird did a 160/170mm travel buke, although i do also have a thing for carbon. The Tyee has anti figures of 130% i have read, and is widely reported as being an incredible climber, but with a trade off in suppleness on descents. I know the am9 has quite high anti squat, but dont know exact figure. Anyone willing to guess how the Tyee would feel downhill compared to the am9, which i have ridden before, and thought was an amazing bike.
Cheers.

Posted: Jan 22, 2020 at 2:52 Quote
I'd like to start off by clearing up some things about pedaling anti-squat.

The Tyee has 120% anti-squat. It also has 380%. Anti-squat is not an absolute number: it depends on the sprocket combination, the amount of sag, whether the bike is compressing in heave or pitch (or some custom blend), and the assumed location of the centre of mass. Unless all these things are standardized, it is impossible to compare numbers and there's not really such a thing as "the exact figure".

Conveniently, I have standardized models for about 600 bikes, so off we go ...

• The Tyee and AM9 both have above-average levels of pedaling anti-squat. Their curves have different shapes, but it's reasonable to call them similar.
• The axle path of the AM9 is a touch more rearward. Again, they're similar. Slight advantage to the AM9.
• Motion ratio curves are both progressive, moreso for the AM9. Thus, the AM9 will be a bit more "glued to the ground" and the Tyee will be a bit more "poppy", all else being equal. Not hugely different, though. If you use the soon-to-be-released, less progressive link for the AM9, they should be quite similar.
• Geometry is pretty similar if you compare based on actual size, not nominal size - ex. compare a size "ML" AM9 to a Large Tyee.
• Stiffness is impossible to compare from my numbers. That said, the AM9 isn't especially stiff and I'm hearing the Tyee is similar.

Overall, they're pretty similar.

Posted: Jan 22, 2020 at 3:25 Quote
R-M-R wrote:
I'd like to start off by clearing up some things about pedaling anti-squat.

The Tyee has 120% anti-squat. It also has 380%. Anti-squat is not an absolute number: it depends on the sprocket combination, the amount of sag, whether the bike is compressing in heave or pitch (or some custom blend), and the assumed location of the centre of mass. Unless all these things are standardized, it is impossible to compare numbers and there's not really such a thing as "the exact figure".

Conveniently, I have standardized models for about 600 bikes, so off we go ...

• The Tyee and AM9 both have above-average levels of pedaling anti-squat. Their curves have different shapes, but it's reasonable to call them similar.
• The axle path of the AM9 is a touch more rearward. Again, they're similar. Slight advantage to the AM9.
• Motion ratio curves are both progressive, moreso for the AM9. Thus, the AM9 will be a bit more "glued to the ground" and the Tyee will be a bit more "poppy", all else being equal. Not hugely different, though. If you use the soon-to-be-released, less progressive link for the AM9, they should be quite similar.
• Geometry is pretty similar if you compare based on actual size, not nominal size - ex. compare a size "ML" AM9 to a Large Tyee.
• Stiffness is impossible to compare from my numbers. That said, the AM9 isn't especially stiff and I'm hearing the Tyee is similar.

Overall, they're pretty similar.
Well thats great, thanks very much, really appreciate the reply. Do you think with the extra travel the tyee will be maybe a bit more supple downhill? And im presuming the tyee will take grester force to bottom out, due to increased travel?
Cheers.

Posted: Jan 22, 2020 at 3:42 Quote
radiorog wrote:
Well thats great, thanks very much, really appreciate the reply. Do you think with the extra travel the tyee will be maybe a bit more supple downhill? And im presuming the tyee will take grester force to bottom out, due to increased travel?
Cheers.

Not necessarily - and it's only 10 mm, which isn't much.

If you set them up with the same relative (percent) sag, the AM9 will take more force to bottom out. It's very progressive! If you set them up for similar bottom-out properties, the Tyee is probably a bit more compliant, based solely on kinematics. The make and model of shock and the tune on it will be more significant factors.

The AM9 can work well with a Low or Medium compression tune and the Tyee should suit a Medium or High. If we compare both bikes with a Medium tune, the Tyee will be a lot more supple, but it will also need a lot of volume reducers in the positive spring chamber to make up for the lack of damping, assuming both bikes are set up with comparable sag. If we compare a Low tune on the AM9 to a Medium tune on the Tyee, the difference will be much smaller.

Keep in mind that "suppleness" is often the opposite of "control" because you'll need more spring support to compensate for the lack of damper support. A "supple" bike often hits a wall of support when that progressive spring curve kicks in, creating an uneven force profile, and the damper may struggle to handle all the potential energy stored in the spring.

Posted: Jan 23, 2020 at 9:05 Quote
R-M-R wrote:
radiorog wrote:
Well thats great, thanks very much, really appreciate the reply. Do you think with the extra travel the tyee will be maybe a bit more supple downhill? And im presuming the tyee will take grester force to bottom out, due to increased travel?
Cheers.

Not necessarily - and it's only 10 mm, which isn't much.

If you set them up with the same relative (percent) sag, the AM9 will take more force to bottom out. It's very progressive! If you set them up for similar bottom-out properties, the Tyee is probably a bit more compliant, based solely on kinematics. The make and model of shock and the tune on it will be more significant factors.

The AM9 can work well with a Low or Medium compression tune and the Tyee should suit a Medium or High. If we compare both bikes with a Medium tune, the Tyee will be a lot more supple, but it will also need a lot of volume reducers in the positive spring chamber to make up for the lack of damping, assuming both bikes are set up with comparable sag. If we compare a Low tune on the AM9 to a Medium tune on the Tyee, the difference will be much smaller.

Keep in mind that "suppleness" is often the opposite of "control" because you'll need more spring support to compensate for the lack of damper support. A "supple" bike often hits a wall of support when that progressive spring curve kicks in, creating an uneven force profile, and the damper may struggle to handle all the potential energy stored in the spring.
Ok, great informative naswer, thank you. Id imagine id either be running a fox x2 or dhx2 coil.

Posted: Jan 23, 2020 at 16:08 Quote
radiorog wrote:
Ok, great informative naswer, thank you. Id imagine id either be running a fox x2 or dhx2 coil.

Happy to help.

The AM9 with the original link is well suited to a coil; the new link can work well with either. I'm quite happy with the original link.

Posted: Jan 24, 2020 at 4:53 Quote
Hey, just wondering if anyone is selling a coil shock to fit an am9 (230*65)
Cheers!


 
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