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Old 11-18-2011, 12:05 PM   #16
Beemerguru OP
Beemerguru...G/S guy
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Joined: Nov 2006
Location: Foster City, CA
Oddometer: 1,027
Took most of your advice...see post above. Went for more strength and repositioned the muffler mounts so the stress goes into the frame and not as a shear force. The shock now sits about a mm about the frame which should minimize the ovaling potential a bit. No more bend either. The bike will be for world traveling not the PD race so I made the decision that this suspension setup should hold up well within those kind of parameters...or course time will tell

The muffler is actually pretty quiet at speed...less than the Staintunes I usually mount. That is until you romp on it and THEN you get this authoritative bark that means business.

Originally Posted by Airhead Wrangler View Post
The way those shocks are mounted on the subframe still has me pretty worried. The lower frame tabs just weren't designed for that. While all the BMW road models of the 70's got by just fine like that, all the PD race bikes mounted the shocks to the main frame. While monolevers got by with a single m10 bolt for the shocks, it was in a clevis arrangement basically doubling its effective shear strength. Those lower M8 subframe bolts are in simple shear and can easily distort the tabs they bolt into. If this thing sees serious off roading and something breaks, I'm betting on those lower subframe bolts and/or the tabs on the main frame. It could start slowly with the holes getting ovalled and then knocking. Also, the lower leg of the subframe on the right side has a big bend in it to go around the stock shock on an r100gs. This side is not nearly as stiff in tension as it's corresponding member on the left and is prone to lengthening if the supension bottoms out and knocks hard. That will distort the subframe as well as the swingarm. Not trying to shit all over your work, and it is nice work, but as an engineer who spends all day fixing failed structural designs, I'm just expressing sincere concern - especially if you're building this for someone other than yourself.

That muffler idea is pretty cool. Good way of saving luggage width without having to go low with it. Nice.
Greg Hutchinson
BMW Club of Northern California, Ambassador, BMW MOA, Vice President Vintage BMW Club
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