cybrsrce AM831 build

[Maffly]

The spacers just have to serve as bushings to provide some support and reduce friction.  Hopefully hold up fairly well too. I think finding the best material for that may be trial and error. My friend thought his 3D print material would be too brittle. Getting contact with the bearings and getting enough pressure on the carbon would be ideal but maybe tricky.  Do you feel you have found that balance?

[Maffly]

I also think that there may be contact with th bearings without the inner spacers. The bolts were hard stopping on the bearings with no pressure on the carbon in stock form. With outer spacers I think they may be compressing into the bearings and filling up the gap. We are all kind of guessing though.

[cybrsrce]

The spacers just have to serve as bushings to provide some support and reduce friction.  Hopefully hold up fairly well too. I think finding the best material for that may be trial and error. My friend thought his 3D print material would be too brittle. Getting contact with the bearings and getting enough pressure on the carbon would be ideal but maybe tricky.  Do you feel you have found that balance?

I think it is pretty close.  I've had to remove those bolts at least 5 times to make changes to the shock and they are compressed a bit but intact.  Destroyed my rear wheel, from the videos, this weekend just in time for my new wheels to arrive - I would video the flex again but I have a gigantic ugly rear fender on right now.     

[cybrsrce]

I also think that there may be contact with th bearings without the inner spacers. The bolts were hard stopping on the bearings with no pressure on the carbon in stock form. With outer spacers I think they may be compressing into the bearings and filling up the gap. We are all kind of guessing though.

So I initially had the bottom out in the linkage and it was only just making contact with all the bits of the triangle.  Then I added a spacer to just the underside of the bolt head and there was clicking because the bearing had play.  Second washer that contact the bearing got it to where it is now.  It still seems like it flexes more than it should but I don't feel anything wrong on the trail.

I think we may have different stages of the same issue.

[scourge]

You guys are doing good work. I really hope we can figure out a solution  to this issue. If it weren't for the flexy rear end, this frame is about perfect for me.

[JJJ]

You guys are doing good work. I really hope we can figure out a solution  to this issue. If it weren't for the flexy rear end, this frame is about perfect for me.

Someone really needs to show some quantitative flex tests. I see no "qualitative" difference with my Altitude just by pressing with the knee in the middle of the frame. The wheel and tire flex much more than the frame, but again, let's try to come up with something quantitative. I was thinking of holding the front triangle flat on its side and applying a downward force on the rear axle with a scale and measuring the triangle skew at 0 and some significant value, say 20 kg, and then comparing with a similar bike. I still need to find a sturdy setup for doing this at home...

[Maffly]

To me the flex in stock form is obvious an unrideable. It also makes perfect sense when you break down the design of the frame. Without bushings or bearings on the outside of the carbon, you have a major problem. If you do ride like that for a while, it’s very likely the pressed in bearings will come loose and mess up the carbon too. If your bolts fit differently and do make contact with the carbon then a different problem will happen that is just as bad.

Yes cybrsrce I do see the dilemma. Probably depends on the tolerances in there and how thick/compressible the nylon washer is. The right washer would take up the space, compress in and allow contact with the bearings as well. Might be some luck involved. Gonna try with just the outer washers first. Feels very solid and pretty smooth right now so we will see.

[cybrsrce]

Someone really needs to show some quantitative flex tests. I see no "qualitative" difference with my Altitude just by pressing with the knee in the middle of the frame. The wheel and tire flex much more than the frame, but again, let's try to come up with something quantitative. I was thinking of holding the front triangle flat on its side and applying a downward force on the rear axle with a scale and measuring the triangle skew at 0 and some significant value, say 20 kg, and then comparing with a similar bike. I still need to find a sturdy setup for doing this at home...

If your seat stays don't look like they're rolling when you move the wheel then just go enjoy riding the bike, you don't have this problem.  Stop looking for it, stop blaming wheels, move on.

[scourge]

I have a video of mine flexing, but can't figure out how to attach it here.

[scourge]

Here is mine flexing:

[Maffly]

That does not look good to me. Maybe not quite as wobbly as mine but close.

[cybrsrce]

Here is mine flexing:

Washers should clean up that slack.  I didn't see a lot of lateral/torsional flex but you moved your wheel gentler than I did.

[scourge]

Yeah, I am not happy with the flexing. I am hoping to find a solution  for it. Thanks again for the work you guys are doing on this.

[JJJ]

The spacers are going to have to serve as bushings because of a design flaw with this frame. If there is not pressure on the carbon pushing the bearings on to the upper link, you are relying on the strength of the bearings bond with the upper link to provide stability (not good). Because you need pressure on the carbon of the upper link and this link needs to pivot, it is essential in order to prevent wear and to not bind the suspension that the material used can be low friction.  I think if the bearings were pressed from the outside, this frame would work very well.

Posted some drawings showing the issue here: http://chinertown.com/index.php/topic,3172.msg32493.html#msg32493

[Maffly]

Nice work JJJ. only thing I would say is that the bearings from the outside would work. Yeti does this for example. That said, none of our re-engineering ideas matter much if the company is not stepping up to make this right.  There would need to be a new mold for the rear triangle and new ones sent out to us all.  We could all press for refunds.