Considering a homemade build

[Burner]

Hectic man. I moved provinces and it was a lot to handle

[nolipoli]

Initial assembly done!

I definitely have some work to do on the cable routing, and the seat post needs to be able to go in deeper (the seat tube got warped in welding). I am going to get a 27.2 dropper with a shim which should work.

 

Other than that, my first pedal around feels really good. I am looking forward to testing it properly

 

[nolipoli]

So after a few rides the news is not good...

 

Too much flex in the rear end, caused mainly by play in the seat stay pivots (rose joints), and the shock mount have me questioning the long term reliability of this setup.

 

I will now set about making a new seatstay arrangement for better stability.

 

Oh well, I guess that's how we learn.

[Captain Fastbastard Mayhem]

Bad news, but good news. Onwards!

[jimmy hardtail]

Rose joints have movement in all directions i think. That and the distance between the rose joint and the shock mount is probably your problem. Some sort of dog link onto the seat tube would help, as well as swapping out the rose joint for a plain bearing or even a bushing

[JXV]

I would like to offer an alternative opinion to the seatstay theory. Your seatstay/shock setup has little resistance against lateral flex even if you fit stiffer joints . The top of the shock is mounted via a plastic bushing to the 2 little triangles that form the mount. The shock/seatstay is effectively a long beam to the rear axle pivots. The plastic bushing at it's head cannot offer much resistance to lateral or torsional forces applied at the other end so the bike must rely on a very stiff chainstay setup for this type of seatstay setup.

 

The chainstays and their pivot point on the seat tube must resist all the lateral and torsional forces induced by the rear wheel in cornering because the seatstay setup is not going to help much in this regard. I suspect the flex problem is originating in the chainstays and I doubt that working on the seatstay design will make much improvement, unless you add a flexible joint at the foot of the shock and a 'dog link' to control lateral seatstay movement at the seat tube as suggested......and this changes the whole dynamic response of your design.

 

 

 

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Edited November 5, 2016 by JXV

[nolipoli]

JXV, I was thinking the same thing about the Chainstays.

What I will start with is to box in the whole area around the tire, hopefully getting a lot more stiffness there.

 

Then I will re-assess before changing more.

Interestingly, I noted a while back that Cotic use an aluminium swingarm on their steel Rocket, and now realize that this might be to increase stiffness.

[Burner]

So after a few rides the news is not good...

 

Too much flex in the rear end, caused mainly by play in the seat stay pivots (rose joints), and the shock mount have me questioning the long term reliability of this setup.

 

I will now set about making a new seatstay arrangement for better stability.

 

Oh well, I guess that's how we learn.

Great Progress Nolipoli!!!! I know it can seem disappointing but believe you me, you are progressing well and learnt even more than you realize right now. 

 

My suggestions are as the following images display, either a doglink as referred to before or reinforce the rear triangle as you've effectively created a single pivot and will need larger rear pivot bearings:

http://ep1.pinkbike.org/p4pb11484589/p4pb11484589.jpghttp://www.carbonalbike.com/media/catalog/product/cache/1/thumbnail/700x/17f82f742ffe127f42dca9de82fb58b1/t/i/titanx_27.5_sl-650b_mtb_full_suspension_frame_carbonal_carbonality_1_.jpghttp://blistergearreview.com/wp-content/uploads/2013/07/High-Single-Pivot.jpg

Edited November 7, 2016 by Burner