Bird Aeris owners thread

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Posted: Apr 5, 2021 at 3:30 Quote
colourofsound wrote:
So these damping curves are independent of the bikes linkage; what you’re describing here is only the damping curve of the shock?

"Damping", and yes, damping curves pertain only to the damper, though the motion ratio curve of the linkage has an effect by altering the ratio of real wheel velocity to shaft velocity.


colourofsound wrote:
If I’ve understood correctly then, linkage curves and dampening curves work in concert to create the feel of the bike.

Yes, and the shock spring curve.


colourofsound wrote:
And, if most shocks are digressive, then a lot of linkage curves must be very progressive to create progressive or linear feeling?

No. Damping is a function of velocity and the motion ratio is a function of position. "Progressive", "linear", etc. have different meanings when they refer to the three systems (motion ratio curve, damper curve, spring curve). If a frame or shock is "progressive", then it's progressive with respect to position; if a damper is "progressive", it is progressive with respect to velocity.

All three curves combine to create the "wheel rate", which is a function of both position and velocity. A wheel rate curve over the whole range of travel would be valid for only one velocity curve. This gets complicated, since we're not dealing with a constant velocity, but a velocity curve. An impact start at zero velocity, reaches a maximum, and goes back to zero at whatever point in the travel the wheel begins to rebound. Automotive racing - especially oval track racing - can predict the velocity curve fairly well, since the speed and the track "terrain" are fairly consistent. Mountain biking is just too messy for this to work well, so it's impractical for suspension designers to try to model and predict ideal behavior from behind a desk. The most practical approach is to test a variety of set-ups in real-world conditions and observe the speed, chassis stability, and rider feedback.


colourofsound wrote:
I’m assuming then that the MegNeg/Coil shocks have linear dampening curves (comparative to most stock air shocks) which gives them the supple small bump and more mid-stoke support generally attributed to these shock types?

Again, you're confusing velocity and position. Spring curves are a function of position, much like a frame's motion ratio curve. The three systems:

• Motion ratio (frame): Function of position
• Spring curve (shock or fork): Function of position
• Damping curve (shock or fork): Function of velocity

The two that interact most closely are the motion ratio and the spring, as these are both functions of position. If the motion ratio is highly progressive, the spring doesn't have to be as progressive, which is why, for example, an extremely progressive Bird AM9 v1 linkage produces an excessively progressive wheel rate when combined with a progressive shock air spring. The moderately progressive AM9 RRR linkage works better with a progressive shock air spring.

Posted: Apr 5, 2021 at 4:23 Quote
Right, I think I see.

This is why I’m not an engineer Smile

As ever, your advice is both detailed and plentiful; thank you.

Posted: Apr 5, 2021 at 7:05 Quote
Sigh.

Turns out I’d misread the manual; and didn’t even realise there was a rebound dial. I thought the 3 position switch was the rebound.

So, I’ve now set the rebound to one click off the quickest, sag is around 32% and the LSC position is set to the minus as per Birds recommendation for their platform.

Re: Forks - I’ve dropped these to about 25% sag and upped the LSC to about 5 clicks.

Lesson: read the manuals - properly.

Posted: Apr 11, 2021 at 3:50 Quote
colourofsound wrote:
Sigh.

Turns out I’d misread the manual; and didn’t even realise there was a rebound dial. I thought the 3 position switch was the rebound.

So, I’ve now set the rebound to one click off the quickest, sag is around 32% and the LSC position is set to the minus as per Birds recommendation for their platform.

Re: Forks - I’ve dropped these to about 25% sag and upped the LSC to about 5 clicks.

Lesson: read the manuals - properly.

I dunno learning lessons is overrated, I think I prefer continually making the same mistakes Wink

Posted: Apr 17, 2021 at 1:43 Quote
I have ordered an AM9. I ride with oval chainring and am wondering what the max chainring size is the AM9 V3 will take. Read that the V1 was max 32t round (30t oval). Is this still the same on the V3? Anyone know?

Posted: Apr 17, 2021 at 2:12 Quote
The V3 chainstay yoke is not smaller than the previous yoke. It's either the same, with a plate welded over the open underside to make a fully boxed profile, or it's slightly larger. Either way, I can't imagine the clearance being any more than before.

Posted: Apr 17, 2021 at 2:52 Quote
MTBRemco wrote:
I have ordered an AM9. I ride with oval chainring and am wondering what the max chainring size is the AM9 V3 will take. Read that the V1 was max 32t round (30t oval). Is this still the same on the V3? Anyone know?

I'm running a 32T round ring on my V3, not a lot of room left for a bigger chainring. As far as I remember, I believe I had the same clearance on the V1

Posted: Apr 17, 2021 at 9:51 Quote
Thanks guys. 30t oval it is.

Posted: Apr 29, 2021 at 2:39 Quote
I've just found that I've snapped my bottom bracket pivot axle, the threaded part has sheared off. I have unscrewed the small broken threaded part out of the chainstay and removed the bolt that expands the collet. Now I'm just left with the rest of the axle still in the frame, it can spin in its current position both ways but a few good taps with a mallet and drift hasn't moved it. I'm assuming the axle was only threaded into the chainstay and that the remaining part is just stuck through friction or corrosion. Just thought I'd ask before getting a big hammer out!



Posted: Apr 29, 2021 at 2:49 Quote
DC1988,

Bummer. Yes, threaded only on the one end. Is it possible a few threads are still engaged?

If your axle was the aluminum version, those simply aren't up to the job. Bird has been using steel axles for some time.

Posted: Apr 29, 2021 at 2:52 Quote
The material modification was done somewhere between the V1 and V2 AM9s right?

Posted: Apr 29, 2021 at 2:55 Quote
Not sure. I thought my v1 AM9 came with steel hardware, while my v1 Aeris 145 had aluminum. Maybe the v1 AM9 had steel ... ? Don't recall.

Posted: Apr 29, 2021 at 3:03 Quote
By the way, a slight tangent, but still related to Bird's pivots. One thing I noticed is that once the hardware is more "weathered" the 6Nm specified for the cone screw that expands the collet might not be enough for it to have a tight fit in the frame. What I do is apply threadlocker in the threads but grease in the cone head. This way the 6Nm provide a perfect fit.
Might sound obvious, but I guess it wouldn't hurt to leave it here

Posted: Apr 29, 2021 at 3:10 Quote
R-M-R wrote:
DC1988,

Bummer. Yes, threaded only on the one end. Is it possible a few threads are still engaged?

If your axle was the aluminum version, those simply aren't up to the job. Bird has been using steel axles for some time.
There are no threads in the chainstay as I can move it away from the main triangle, I think perhaps where it has sheared it might have flared a bit hence not easily sliding back through. As there are no threads in the rest then I will hit it harder. I assume it's a V1 Aeris 145, I got it 2nd hand about 6 months ago and the previous owner said it was in his shed for a few years. It's definitely an alloy pivot, it's good to hear they are now steel.


 
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