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Old 06-19-2010, 03:46 PM   #1
Raven Wilde
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Default Girders and "Wobble"

Hey
I have been searching the net about girder front ends and came across several that mention that a girder wobbles at LOW SPEEDS.
I have been trying to wrap my head around this for about 2 weeks now and all I can think of is WTF!?
I have experienced "wobble" with my stock front end at 100mph and over but I understand that.
Anyone know about this low speed wobble and giders?
Thanx
RaVen
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Old 06-20-2010, 10:57 AM   #2
Kenneth_Moore
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Girder front ends have enormous potential for wobble, as they throw good suspension design out the window for the sake of appearance. Back in the '70's they were haught sheit, but a lot of guys wound up on the asphalt because of them.

If you really want that look, go for a HD Springer front end, at least they're functional.
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Old 06-20-2010, 12:52 PM   #3
Raven Wilde
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Default wobble wobble wobble

Thanks for the re: Kenneth!

So, a girder will wobble not just at low speed but at any speed? Any idea what causes this wobble? Is it the front ends construction in general, the spring tension, tire shape/size, incorrect rake/trail?
All of the above? LOL!

I was searching for an old twisted springer, not the new one with the little shock on them. Not easy to find.
What info I found was, that new or old style, they were the equivalent of a pogo stick with a wheel on it.

As for "Good Suspension Design", that went out the window LOOONG ago. Some good intentioned but not too intelligent soul, chopped the frame and welded on the wishbone, crooked. So she handles like lopsided BRICK

I love the "Vintage Choppers" of the 70's. I already had an old girder from the 60's-70's laying around, so I would like to use it to keep it truely "authentic" to the era.
I am in the design phase for a custom frame for my '71 XLCH, and was curious if there was something in the design of the frame that could help in reducing the wobble factor.
I would not ride her at break neck speed anyway. How can anyone admire a piece of Art if it goes flying by at 100, wipes out, then bursts into a fireball
Although she is more than capeable of high speed insanity, and I am at handling it, I'm looking to build an "Artful Putter".
Any suggestions for wobble reduction in the frames construction?
Thanx Again
RaVen
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Old 06-20-2010, 03:46 PM   #4
seruzawa
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Quote:
Originally Posted by Raven Wilde View Post
Thanks for the re: Kenneth!

So, a girder will wobble not just at low speed but at any speed? Any idea what causes this wobble? Is it the front ends construction in general, the spring tension, tire shape/size, incorrect rake/trail?
All of the above? LOL!

I was searching for an old twisted springer, not the new one with the little shock on them. Not easy to find.
What info I found was, that new or old style, they were the equivalent of a pogo stick with a wheel on it.

As for "Good Suspension Design", that went out the window LOOONG ago. Some good intentioned but not too intelligent soul, chopped the frame and welded on the wishbone, crooked. So she handles like lopsided BRICK

I love the "Vintage Choppers" of the 70's. I already had an old girder from the 60's-70's laying around, so I would like to use it to keep it truely "authentic" to the era.
I am in the design phase for a custom frame for my '71 XLCH, and was curious if there was something in the design of the frame that could help in reducing the wobble factor.
I would not ride her at break neck speed anyway. How can anyone admire a piece of Art if it goes flying by at 100, wipes out, then bursts into a fireball
Although she is more than capeable of high speed insanity, and I am at handling it, I'm looking to build an "Artful Putter".
Any suggestions for wobble reduction in the frames construction?
Thanx Again
RaVen
The girder has several bearing points and a complex linkage. There is a lot of potential for too much tolerance at these points which causes the entire unit to twist and move side to side minutely. These movements are multiplied by the length of the girder to the wheel. I supposed if one spent thousands on a precision built girder it might not wobble. They aren't being built that way. These are built by some guy in a garage.
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Old 06-20-2010, 04:24 PM   #5
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it's just sticks for suspension, really. Ken's right about the springer. Wanna go off the springer norm? Contact Revolution Revolution Speed ask about the inverted springer front end. It's truly the coolest on the market.
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Old 06-20-2010, 05:17 PM   #6
sarnali2
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Well first off you'll need a GOOD bike shop specializing in HD. Then cut the wishbone out, cut it off even on both down tubes and engine cradle, add a solid steel bar (slug) in each side that fits inside the tubes, have it welded in then cut some pipe the same OD as the frame and slip it over the slugs. Stick the ends in the down tubes and frame behind the engine cradle and weld it up straight this time.

Or, spend some bucks at Paughco and get a new frame. You can spec out a Sporty rigid frame for your engine for under a grand. I would recommend stock rake and backbone with 2 inches of stretch in the downtubes, then run about a 6 to 8 over springer. That'll give you a nice looking set on the bike with the engine and frame a little off level, that's the way we used to do them back then. If you just add a longer front end the engine sits up to high and f*cks up the center of gravity, long and low handles pretty good for a chopper.

I personally wouldn't screw around with a bent or misaligned frame, that's a pretty good way to wind up dead or crippled. Just spend the money on a new frame, it's not much, it comes with papers and Paughco has been around since the old days, they know their business.
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Old 06-22-2010, 04:15 AM   #7
Raven Wilde
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Wink

Thanks for all the input and great advice. Keep it commin please, even the slightest notion might be the idea that will figure out something that had me stuck

The frame she sets on now is going into the scrap pile. It served its time, it deserves to be laid to rest after 40 years of abuse. I myself rode it like it was a dirt bike...LOL!

Luckily I have a good friend who doesn't specalize in HD but in CHOPPERS. He has built several truely amazing choppers, all perfectly balanced, safe (as choppers go) and functional.

Today I was sitting in friends garage and saw one of those racing dirt bikes setting in the corner. I thought, well they take HELL of a beating and decded to check out the construction of the neck, backbone and down tubes on it. I think I have come up with something that might work for the abuse it will endure. Then I looked at his mud bogger and saw that EVERYTHING on it was carefully and precisely built for a specific purpose.

As for the girder itself I have a few ideas to sturdy it up a bit to reduce the wobble factor, without ruining the original vintage look.

Thanx!
RaVen

It's kind strange. I am an artist by trade and can make anything into a motorcycle in a drawing. I never considered the extent of engineering that went into creating one that to be functional. I have a TOTALLY new appreciation for them now.
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