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Author Topic: BMW R90/6 Cafe  (Read 8199 times)

Offline ncologerojr

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    • Catskill Mtn. Customs
Re: BMW R90/6 Cafe
« Reply #30 on: Jun 21, 2018, 05:51:42 »
Are you going to stiffen up the cradle so it's not a rubber cow anymore?  Curious if that will get even worse (or better) now that it's a mono shock. Considering where your top mount is, I don't have as high of hopes.

Iíll do what I can. With the original bolt-on subframe, the rear section of the frame was not tied together well and able to twist independently with the swingarm. My rear subframe ties that area together. I donít see why my shock mount would concern you. With the rear tubes converging in that area itís pretty supported...

Online farmer92

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Re: BMW R90/6 Cafe
« Reply #31 on: Jun 21, 2018, 06:28:11 »
It would concern me as well.
With the original mounts there was zero load on the SA pivots (next to zero anyway)
The shock loads were countered by the lower subframe mounts and they look to have a load of about 1.25x the shock load.

Wit your new mono-shock mount you have greatly increased the leverage on the shock, and obviously also the forces, but this greatly increases the load on the SA pivot.
To my point


The slight downward angle helps out a bit in reducing the forces but you are probably now putting double the wheel load into the SA pivots.
You are also forcing the top end of the cradle forwards with double the wheel load but that is less of a concern here.

Online farmer92

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Re: BMW R90/6 Cafe
« Reply #32 on: Jun 21, 2018, 06:33:33 »
Also, it looks like you have a regressive rate geometry on the rear suspension.
If the shock angle changes and slowly becomes more vertical as it compresses then that is indeed the case. Itís hard to tell from the photos though.

Offline irk miller

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Re: BMW R90/6 Cafe
« Reply #33 on: Jun 21, 2018, 08:19:16 »
Have you ever ridden an airhead?  They didn't earn their rubber cow moniker for nothing. LOL . Between the orientation of the motor/crank rotation and the featherbed-like design of the frame, they are extremely sloppy in turns.  It's a very soft, noticeably rubbery effect.

Offline ncologerojr

  • Posts: 789
    • Catskill Mtn. Customs
Re: BMW R90/6 Cafe
« Reply #34 on: Jun 21, 2018, 09:12:05 »
It would concern me as well.
With the original mounts there was zero load on the SA pivots (next to zero anyway)
The shock loads were countered by the lower subframe mounts and they look to have a load of about 1.25x the shock load.

Have you ever ridden an airhead?  They didn't earn their rubber cow moniker for nothing. LOL . Between the orientation of the motor/crank rotation and the featherbed-like design of the frame, they are extremely sloppy in turns.  It's a very soft, noticeably rubbery effect.

Gotcha, I see what you guys are getting at now. The way I read Irkís first post I thought he was talking about the top shock mount specifically failing or something, now that I re-read I see what you were saying.

Yeah, these frames are known for flex. The first thing I did was start looking at road race bikes to see how those guys deal with it. Actually, first thing I did was consider build a new frame, but itís not in the budget. I plan to make braces like guys run on their race bikes (pic below), but I need to get everything else in place first to avoid clearance issues. Iíve been thinking over supports in the rear coming from the SA mounts and running to the top shock mount, and a cross brace at the SA mounts to triangulate the area. Similar to whatís in the picture. If you look close, you might or be able to tell in the pictures, the top shock mount isnít completed because I am considering using it as a landing pad for the rear braces.




Offline BenHolmes21

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Re: BMW R90/6 Cafe
« Reply #35 on: Jun 21, 2018, 09:37:25 »
Incredible work on this! Canít wait to see the end result!!


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Offline ncologerojr

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Re: BMW R90/6 Cafe
« Reply #36 on: Jun 21, 2018, 09:54:32 »
Incredible work on this! Canít wait to see the end result!!


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Thanks man!

Online farmer92

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Re: BMW R90/6 Cafe
« Reply #37 on: Jun 21, 2018, 10:12:10 »
That bracing will be just the ticket!
Awesome work

Offline Hurco550

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Re: BMW R90/6 Cafe
« Reply #38 on: Jun 21, 2018, 10:19:18 »
 Beautiful work as always on the body work! Thanks for sharing it here. And yeah, can't argue that my R90/6 doesn't feel a bit "wet noodly" when pushing it into a turn lol

This one has an entirely custom frame (I think) but its another idea for bracing none the less.

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"If you just picked up a drug habbit instead of a kawasaki triple at least you could get high while you waste money"
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1988 tw200, the swamp donkey: http://www.dotheton.com/forum/index.php?topic=75455.0
2006 Suzuki DR650 Adventure monowheel trailer build: http://www.dotheton.com/forum/index.php?topic=75033.0
1976 BMW R90/6 farkilitious: http://www.dotheton.com/forum/index.php?topic=74349.msg882477#msg882477
1975 RD350 Road Racer: http://www.dotheton.com/forum/index.php?topic=70652.msg833688#msg833688
1976 GT250 Rebuild: http://www.dotheton.com/forum/index.php?topic=64973.new#new
Full Custom Pit Bike: http://www.dotheton.com/forum/index.php?topic=66954.new#new
1971 Yamaha 90cc twin HS1: http://www.dotheton.com/forum/index.php?topic=70498.0
"much ingenuity with a little money is more profitable and amusing than much money without ingenuity" - Arnold Bennet

Offline canyoncarver

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Re: BMW R90/6 Cafe
« Reply #39 on: Jun 21, 2018, 14:21:44 »
Sweet stuff.  Love the tank!
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YZF750/1000R The Fly
KZ 750 Twin
ZRX 1100
KZ400 The Rabbit
KLR650, 73 Norton Commando, my never finished shovelhead chopper, an 86' FXR, and an F9 Bighorn
more YZF750R's, more KZ's, a Zephyr750...and the ever unfinished 75' CB550 cafe.
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