Bagger wobble exposed!
Banned
Joined: Apr 2014
Posts: 678
Likes: 1
From: LA
What makes the FXR frame stiffer? Has the actual metal got anything to do with it?
I agree that the matter has been discussed all over the place but no one has taken the question to its require conclusions of,
a) speaking to the engineers who built it and getting a good answer from them, or
b) sticking a frame in a jig and measuring how and where it flexes. Presumably H-D did this at some point?
I think I know of one person might have tried sticking a jack between the frame and measuring how much they would flex. I don't know of anyone who has tried twisting one ... which is strange as presumably a few have ended up in frame shops to be repaired ... but really the problem is discussion dries up at the point where it all becomes guesswork and theory.
Can someone ask Tony Foale, Fritz Egli etc?
Everyone it seems, including those selling solutions, is guessworking it seems and applying bandaids to influence things.
No takers for bracing the frame at any point? This new device appears in essence to use the swing arm pivot to do so.
I agree that the matter has been discussed all over the place but no one has taken the question to its require conclusions of,
a) speaking to the engineers who built it and getting a good answer from them, or
b) sticking a frame in a jig and measuring how and where it flexes. Presumably H-D did this at some point?
I think I know of one person might have tried sticking a jack between the frame and measuring how much they would flex. I don't know of anyone who has tried twisting one ... which is strange as presumably a few have ended up in frame shops to be repaired ... but really the problem is discussion dries up at the point where it all becomes guesswork and theory.
Can someone ask Tony Foale, Fritz Egli etc?
Everyone it seems, including those selling solutions, is guessworking it seems and applying bandaids to influence things.
No takers for bracing the frame at any point? This new device appears in essence to use the swing arm pivot to do so.
Thread Starter
|
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,897
From: Bedford UK
DR,
A friend of mine was a development engineer at BSA, way back. They did torsion tests on 650cc BSA, Triumph and Norton featherbed frames in the late 60s/early 70s. The test machine they used couldn't do so with engines installed. The BSA frame was stiffest, Triumph next, then the Norton. However in reverse order they used more mounting points at which the engine/trans was bolted in, suggesting that on the road the Norton and Triumph would be closer to the BSA.
For a rubber mount engine, like a Commando or H-D, the frame stiffness is more critical, however all forms of vehicle depend upon a level of forgiveness in their chassis/frame, otherwise passenger comfort and vehicle longevity are totally dependent on the suspension. I don't believe we have reached a point when suspension can cope with an infinitely stiff chassis/frame!
The FXR and FLT frames bear a close resemblance to Colin Seeley's frames of the 70s, so they have good heritage. As for adding extra bracing to a frame, the risk is that localised additional bracing may create stress points and undo the basic integrity of the existing frame. Despite the routine and stereotyped unkind comments made about the MoCo, they have been using sophisticated techniques in their design and development since the AMF days - who invested heavily in design and development facilities.
That doesn't answer you, but I have never seen anyone comment on HDF who has a declared (or even apparent) direct knowledge of things H-D! Hence my attempt to clarify the rubber-mount thang here.....
A friend of mine was a development engineer at BSA, way back. They did torsion tests on 650cc BSA, Triumph and Norton featherbed frames in the late 60s/early 70s. The test machine they used couldn't do so with engines installed. The BSA frame was stiffest, Triumph next, then the Norton. However in reverse order they used more mounting points at which the engine/trans was bolted in, suggesting that on the road the Norton and Triumph would be closer to the BSA.
For a rubber mount engine, like a Commando or H-D, the frame stiffness is more critical, however all forms of vehicle depend upon a level of forgiveness in their chassis/frame, otherwise passenger comfort and vehicle longevity are totally dependent on the suspension. I don't believe we have reached a point when suspension can cope with an infinitely stiff chassis/frame!
The FXR and FLT frames bear a close resemblance to Colin Seeley's frames of the 70s, so they have good heritage. As for adding extra bracing to a frame, the risk is that localised additional bracing may create stress points and undo the basic integrity of the existing frame. Despite the routine and stereotyped unkind comments made about the MoCo, they have been using sophisticated techniques in their design and development since the AMF days - who invested heavily in design and development facilities.
That doesn't answer you, but I have never seen anyone comment on HDF who has a declared (or even apparent) direct knowledge of things H-D! Hence my attempt to clarify the rubber-mount thang here.....
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
Nope..
The FXR frame is pretty much identical to the the bagger frame except that the changed the geometry in the front and added a bunch of weight.. Those 2 changes amplify any flexure at the rear mount and create the wobble.. Pulling the fairing off the forks helps as does reducing fork weight.. One thing that is different in the fork geometry is that the pulled all the mass closer to the central pivot point to help make all the mass feel lighter.. This probably add to the instability..
Those thinking that Yamaha successfully isolated the motor from the swingarm need to look closer.. They used a drive shaft which is very tolerant of miss alignment. Chain not so much. Belts almost no tolerance..
Road Captain
Joined: Aug 2012
Posts: 622
Likes: 2
From: Connecticut
So on a Harley we have a shaft that passes thru the isolator, swing arm and transmission and then the same on the other side. The isolator is resilient and can allow the entire mass to move.
If the frame swing arm and transmission engine are all mounted on the same shaft but the isolation is in the middle on the transmission why would the transmission get out of alignment any worse than the entire drivetrain if rubber mounted in the frame? Proper belt tension and the same third link would prevent any misalignment, maybe?
If the frame swing arm and transmission engine are all mounted on the same shaft but the isolation is in the middle on the transmission why would the transmission get out of alignment any worse than the entire drivetrain if rubber mounted in the frame? Proper belt tension and the same third link would prevent any misalignment, maybe?
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
So on a Harley we have a shaft that passes thru the isolator, swing arm and transmission and then the same on the other side. The isolator is resilient and can allow the entire mass to move.
If the frame swing arm and transmission engine are all mounted on the same shaft but the isolation is in the middle on the transmission why would the transmission get out of alignment any worse than the entire drivetrain if rubber mounted in the frame? Proper belt tension and the same third link would prevent any misalignment, maybe?
If the frame swing arm and transmission engine are all mounted on the same shaft but the isolation is in the middle on the transmission why would the transmission get out of alignment any worse than the entire drivetrain if rubber mounted in the frame? Proper belt tension and the same third link would prevent any misalignment, maybe?
Thread Starter
|
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,897
From: Bedford UK
If the frame swing arm and transmission engine are all mounted on the same shaft but the isolation is in the middle on the transmission why would the transmission get out of alignment any worse than the entire drivetrain if rubber mounted in the frame? Proper belt tension and the same third link would prevent any misalignment, maybe?
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From: Oxford, Nc
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