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Old 01-16-2015, 07:46 AM   #1
akolleth OP
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parallel struts? need help from sidecar builders-

I am working on the germ of an idea to build my own subframe for a Goldwing 1000. Working out the details and ran across a question I could use some help on. If I go the route of building my own subframe I would also build new attachment points on the sidecar frame. That way I can make the struts any angle I so desire and not be dictated by the strut locations that exist already on the sidecar.

On all the mounts I have seen here the upper and lower struts form a triangle. Is there a reason not to make the struts parallel? I could set the upper and lower struts to be parallel (when viewed from the front) and the front and rear ones parallel to each other (when viewed from the top). So in essence making the four struts resemble a box in shape. Or I could also make the upper and lower struts into a more traditional triangle shapes, coupled with the front and rear being parallel

Any reason to go with one over the other? Parallel, triangle? Am I over thinking this

akolleth screwed with this post 01-16-2015 at 07:51 AM
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Old 01-16-2015, 08:13 AM   #2
jaydmc
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With the struts at the same angle you have formed a parallelogram which can collapse, With the struts at different angles you have formed a trapezoid which will not collapse. Not that it really make much difference as long as every thing is stout. We try for trapezoid, Ural builds their rigs as parallelogram's and have made a few million this way.

When making your sub frame try and keep the lower mounts equal distance from the ground or the front slightly higher then the rear. This can be tricky on the GL as the frame of the bike does not lend its self to doing this. With the lower rear mount higher then the lower front mount which is often the case on 4cyl GL's when you adjust your lean out your toe moves the wrong way. So if you are leaning it out to fix a pull to the right, you end up with more toe and more pull to the right until you go back and reset your toe.

Our sub frames put the lower rear mount under the muffler and aft of the main frame section.

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Old 01-16-2015, 11:57 AM   #3
DRONE
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Try to imagine building a picture frame with 1" x 1" wood with 45° mitered cuts at each corner. Nail it together using one nail at each corner. Lean it up against a wall, then give it a little push along one edge. The nails pull out and whole thing collapses on the floor, right? Now imagine building the same picture frame, but this time make the top of the frame shorter than the bottom and change the 45° cuts to match the new dimensions. This time, when you lean it up and give it a push it just slides along the floor and keeps it's shape.

This is what Jay is talking about above ^^^^ about trapezoids.
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Old 01-17-2015, 06:33 AM   #4
akolleth OP
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So when you are talking about parrallelagram versus trapeziod, are you talking about looking at them from the top down view?
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Old 01-17-2015, 07:21 AM   #5
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Quote:
Originally Posted by akolleth View Post
So when you are talking about parrallelagram versus trapeziod, are you talking about looking at them from the top down view?


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Old 01-17-2015, 09:29 AM   #6
DRONE
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Originally Posted by akolleth View Post
So when you are talking about parallelogram versus trapezoid, are you talking about looking at them from the top down view?
Well, yes, but think about it. A trapezoidal strut configuration as viewed from above looking down at the ground gives the outfit fore-'n-aft rigidity for braking and accelerating. But you also want a trapezoidal configuration as viewed from the front to give you up and down rigidity.

As Jay stated above, if the construction is stout enough then parallel struts can be made to work. Jay mentioned the Ural configuration. On my GS rig built by DMC the two lower struts are parallel both from above and from the front (though they both have an A-arm brace built into the design for rigidity). My two upper struts are trapezoidal, both in relation to each other and in relation to the lower struts.

You've read this thread I assume? -- Sidecar Design Formula - IMPORTANT!
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Old 01-17-2015, 02:11 PM   #7
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The more opposing angles the better.
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Old 01-17-2015, 07:47 PM   #8
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Okay pretty sure I got it. its a truncated pyramid shape we want. I slapped together this incredibly well drawn picture to make sure I am understanding the geometry

This would be looking at it from the side standing where the sidecar would be. The struts are the red lines. The black lines in teh back would be a subframe on the bike, the black lines in front would be a subframe on the sidecar. The green dots are where the struts would connect to the sidecar, and the lilac dots are where the struts would connect to the Bike itself.

I am thinking this design would create trapeziods both front to back and side to side

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Old 01-17-2015, 07:59 PM   #9
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Quote:
Originally Posted by akolleth View Post
Okay pretty sure I got it. its a truncated pyramid shape we want. I slapped together this incredibly well drawn picture to make sure I am understanding the geometry

This would be looking at it from the side standing where the sidecar would be. The struts are the red lines. The black lines in teh back would be a subframe on the bike, the black lines in front would be a subframe on the sidecar. The green dots are where the struts would connect to the sidecar, and the lilac dots are where the struts would connect to the Bike itself.

I am thinking this design would create trapeziods both front to back and side to side



Back to the drawing board, for you.

Without dimensions, the drawing means squat.




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Old 01-18-2015, 01:35 AM   #10
claude
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Lower mounts can be parallel when viewed from top. What Jay said about the lower mounts is important. Just to add to it you also should have them (the hinge point at the subframe) the same distance from the center of the bike. If you think about it when the bike is leaned out these mounting points are rotating in an arc with the center of it being the centerline of th ebike tires at ground level. So if they could move on the same arc that would be good but having the front one a little higher or closer to the sidecar adds insurance that the sidecar wheel does not go into a toe out situation when lean is adjusted. On any sidecar outfit it is good to check how lean out may affect toe in before messing with the setup. If one has a decent mounting system this is easily done by disconnecting the upper struts and having a helper just lean the bike in and out while you watch the sidecar wheel to see which way it 'steers'. Good thing to know.
Toe out will usually cause a pull to the right. Toe in usually will not be felt. Too much of either will create more tire wear usually on the rear tire of the bike but sometimes on the sidecar tire especially if it is a narrow one. Adding toe in IS NOT the answer to negate a pull to the right (sidecar mounted on right). Lean out or tilt is the answer. Lean the bike in the direction you want to go.
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