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Author Topic: Tank slapper  (Read 1493 times)

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johnmowcop

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Tank slapper
« on: May 18, 2020, 05:26:29 PM »

Not just CVO’s.
Is it endemic of all Harley’s to degenerate into a tank slapper if both hands are removed from the handlebars at any speed.
JohnT
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Twolanerider

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Re: Tank slapper
« Reply #1 on: May 18, 2020, 05:39:02 PM »

Not just CVO’s.
Is it endemic of all Harley’s to degenerate into a tank slapper if both hands are removed from the handlebars at any speed.
JohnT

Any bike might and it can be the result of many different factors; bike, road or otherwise.  And they can do it whether your hands are on the bars or not.
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fastfreddy

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Re: Tank slapper
« Reply #2 on: May 18, 2020, 06:46:03 PM »

back in the olden days.... i had a KZ900 and it would go in to a death wobble at or around 140 mph, turned out i had some worn bushings on the swing arm , replaced bushings and sold that stupid thing   :nixweiss:
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J.D.

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Re: Tank slapper
« Reply #3 on: May 18, 2020, 07:00:39 PM »

Contrary to what seems to be popular belief, you don't need worn parts and/or heavy loading to experience this, although those things may increase the likelihood and/or severity.  I believe the Harley touring front end geometry (rake, trail) is part of it, but I'm not a suspension engineer.  Whatever causes it, it's often unpredictable, scary as hell, and can cause a rider to lose control.
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grc

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Re: Tank slapper
« Reply #4 on: May 18, 2020, 08:14:14 PM »

Contrary to what seems to be popular belief, you don't need worn parts and/or heavy loading to experience this, although those things may increase the likelihood and/or severity.  I believe the Harley touring front end geometry (rake, trail) is part of it, but I'm not a suspension engineer.  Whatever causes it, it's often unpredictable, scary as hell, and can cause a rider to lose control.

The front end geometry of the touring models from the 80's up to 2013 was in fact a contributor to the problem.  In 2014 the front end design was changed to a more conventional design.  I don't remember seeing any front end wobble/tank slapper complaints since then; anyone have any firsthand experience with a Rushed More tank slapper or high speed wobble?

Jerry
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Re: Tank slapper
« Reply #5 on: May 18, 2020, 11:05:47 PM »

OK, I know I shouldn't but regularly hang my arms down for minutes at a time on long stretches on the freeway with Cruise set. Bike solid as a rock
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Alan

J.D.

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Re: Tank slapper
« Reply #6 on: May 18, 2020, 11:22:36 PM »

When I experienced this on a touring bike I was riding 1-up on the interstate at typical interstate speed (cruise control engaged). Low mileage bike, well maintained, newer and properly inflated tires.  Pretty good curve and hit a "dip" in the road during the aforementioned curve.  The front wheel went from tracking solid to fluttering like the front wheel of a bad shopping cart instantly.  Holy f'n hell!  What do you do (after chitting yourself)?  Brake?  Tighten up your arms?  I can't tell you what I did as I can't honestly remember.  Didn't crash it, somehow.
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FLSTFI Dave

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Re: Tank slapper
« Reply #7 on: May 19, 2020, 05:55:32 AM »

OK, I know I shouldn't but regularly hang my arms down for minutes at a time on long stretches on the freeway with Cruise set. Bike solid as a rock

Bored on the interstate going across flat straight Kansas I rode 23 miles with my hands off the bars at 80mph.  It was just to see how far I could go. 

Road glides are very sensitive to neck bearing adjustment, if its off, while deceleration from 55 mph down with hands off bars about 47 the bars will start to go back and forth, and as it slows more it gets more pronounced.  If neck is adjust right it will  not do this.

So when I leave the dealer after service, first thing I do is run up to 55mph, take hands off bars and let bike slow, any shake its back to dealer for them to correct.  Only once did a service writer tell me the issue was not the neck bearing adjustment but that you never take hands off bars.  Service Manager over heard and came out and told him, I was correct, neck was adjusted wrong, most likely to regular touring bike spec.
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