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Re: The Shiny New AM831 Group Buy (A) Thread!
12.2 kg sounds pretty light for a bike of that much travel, do you have a parts list? Essentially: Fork: RS Pike 150mm Shock: Fox DPS EVOL (no piggy-back = almost 200 g lighter), enough for me Cranks: E13 TRS Race Carbon (the XCX Race Mountain are even lighter, but said to be flexy) Wheelset: homemade from Chinese carbon rims (30mm inner width) and DT 240EXP clones, Sapim D-Light spokes = 1385 g Cassette: E13 Helix-R Rear derailleur: XTR Pedals: composite Saddle: Chinese carbon (so damn light and cheap, and perform well) October 10, 2021, 04:04:11 PM |
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Re: The Shiny New AM831 Group Buy (A) Thread!
Rode mine the first time last Saturday, a short ride compatible with my wrist recovery. Ascent with steep technical portions, then a downhill singletrack, flowy at the beginning with small jumps, ending with tight turns in a steep off-camber section. Dry conditions, which make the off-camber bit slippery with loose soil and dust. The climb was way easier, both technically and physically, than with my Rocky Mountain Altitude (same type of bike, but 27.5 wheels and "old" geometry). The descent felt significantly better than with the Altitude. The bike is responsive and grippy, and handles great in the small turns, which I initially doubted with the big wheels. Haven't tried tight switchbacks yet. Shimano drive train switches flawlessly (all Shimano but an e13 cassette). No cables rattling in the frame that I could hear above the rolling noise. The rear triangle is stiff, at least as stiff as my Altitude. October 25, 2021, 04:04:11 AM |
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Re: The Shiny New AM831 Group Buy (A) Thread!
That is with the shims I made from a gallon water bottle, probably .5mm - maybe less. I believe the issue is like FlaMtnBkr said, the bolts are just a few mm too long and bottom out in the back of the linkage. The "proper" fix is probably shorter bolts, whether that is a redesign or a cut and chamfer, but I noticed with the bolts out it is pretty far from the linkage. Pinching it in may actually contribute to the stiffness and I may make it worse by adding larger shims, we'll see From what I gather, there are only two in the group that have the problem. I have no issue and the vast majority of the group probably doesn't either, because we don't post when there is no issue! Mine definitely doesn't flex like that! The shim solution doesn't sound great - is it so hard to mill some mm off the bolt? How does the incriminated bolt compare with the one on the other side? October 26, 2021, 09:33:13 AM |
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Re: The Shiny New AM831 Group Buy (A) Thread!
Seams like an expensive lottery especially if your not able to join a group buy. @Krillle, I didn't correctly prune my quote when I posted my comment. The above is what I reacted to. The point I was trying to make is that the issues are probably scarce and related only to the linkage bolt issue, so you have a good chance at winning the lottery. So how many out there have the bolt issue? I've counted two or three. What about the warranty in that case? We haven't quantified either what an acceptable flex is, so we shouldn't be all worried to note some flex - for now I can only compare it to my other bike and evaluate the riding feel, which is pretty good so far. And sure, it would be nice if spare bolts and other linkage components were available. Speaking of spare parts, the derailleur hanger is available here (choose the FS831 option): https://www.aliexpress.com/item/1005001935571629.html October 28, 2021, 04:44:16 PM |
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Re: The Shiny New AM831 Group Buy (A) Thread!
There was some talk a few pages back regarding what a mud guard for the shock. I had designed and printed myself one a few weeks back that seems to work well. It's held on via a zip and i've attached it for anyone that has a 3d printer. Here is another solution to keep the rear shock somewhat clean. Holds with only two zip ties on the seat stays - not perfectly stable, but has held so far in pretty rough terrain and rough riding. https://www.aliexpress.com/item/1005003325658168.html @geekbox32, I tried to print that fender, but it comes out too thin and crumbles apart. Maybe not the correct plastic. I'll try to add some thickness. November 02, 2021, 05:12:15 AM |
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Re: AM831 competitors? Help knudge me over!
Any frames that you're aware of that can handle a 230x27.5mm shock? if not, I'd have to look into selling it and buying one that fits. That is a very specific shock, rather long with a comparatively tiny stroke! Not sure you'll find AM or enduro frames that will take it. November 08, 2021, 03:27:24 AM |
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Re: AM831 competitors? Help knudge me over!
I pulled the trigger on the AM831 already so it's done. I was interested in the other two as well but for $200 less shipped and colored, I'll go the AM831 route instead. Thx Congrats. So where did you buy it? I got mine from Winow on Aliexpress, missed the group buy deal from Haideli, but a few problems have been reported on the Haideli version, none of which I had with the Winow version... Am I lucky, or is there a quality difference between the various AM831 manufacturers? November 09, 2021, 04:46:21 AM |
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Re: The Shiny New AM831 Group Buy (A) Thread!
It is worth showing the link assembly issues with pictures rather than just words to get the message better across, so I've drawn some (not to scale, dimensions exaggerated, showing the principles). This is the 831 assembly of the upper link to one of the rear triangle eyelets, as far as I could make it out. Grey is the aluminum link, black the carbon triangle, blue the ball bearing and pink the screw. The screw presses the inner race of the bearing against the link, so the screw and inner race are one piece with the link. There is some clearance between the screw head and the triangle so that the parts can rotate with respect to each other. This assembly would be alright if the two eyelets of the triangle (only one shown) were perfectly rigid relative to each other, but that is not the case. So, what prevents the outer bearing from sliding out of the triangle eyelet (to the left) is in practice only the press force of the outer bearing race in the eyelet, as Maffly stated. Inevitably, when the triangle is submitted to lateral forces, the bearing will end up sliding to this position, where the eyelet contacts the screw head, and rubs against it as the triangle and link rotate relative to each other. After a while, clearance may build up between the outer race and the eyelet, whereby the bearing will move freely in and out... The rubbing with the screw head will cause wear and potentially loosen the screw... The situation wouldn't be improved if the bearing were pressed from the outside. The bearings should be in the link, not the triangle, as per the SC assembly shown below. Yellow is a tube for taking up some of the axial force exerted on the bearings by the screw. Here, the bearings are mounted in the link and rely on the rigidity of the link between the two eyelets. The bearings cannot slide out. Dammit, the 831 link and triangle need to be redesigned!! A not too drastic redesign would be to provide something for keeping the bearing in the eyelet, such as a retainer ring. What about the assembly of the lower link to the triangle? I haven't looked close at that yet. November 29, 2021, 04:10:44 AM |
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Re: cybrsrce AM831 build
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 November 29, 2021, 04:29:27 AM |
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Re: The Shiny New AM831 Group Buy (A) Thread!
On my frame, if I pulled on the seat stay there was very obvious movement so I made a washer to fill the gap under the bolt head and the carbon of the frame. This reduced the play but I didn't stop to look at the design and what was actually happening. Since the bolt is holding the bearing tight to the linkage, when the frame moved over the bearing was sliding in and out of the frame. The washer just limits the movement but between the bearing moving in the frame and the bolt rubbing on the frame or washer if installed, things are going to start falling apart pretty quickly. Yes, I guess you're unlucky there. My bearings don't move in and out of the eyelet... yet. But I do have some traces of rubbing from the screw head. I've attached a potential fix, using a second ball bearing on the outside. It does need crafting a custom screw, though. November 29, 2021, 10:38:33 AM |
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