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Old 06-15-2013, 07:12 PM   #16
bigdog99
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The bike walks across the flat tire carcass back and forth. Because the rear contact patch is not "fixed" any longer, the corrective countersteer is a delayed reaction which quickly becomes an overreaction, which feels like a mild "tankslapper". Riders who grew up with the early tube-tired heavyweight bikes in the '70s got to know that initial sink then weave and to quickly react. Most of us had the toes beveled off of our Red Wing work boots from dragging them as outriggers until we could get the whole mess stopped.
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Old 06-15-2013, 10:39 PM   #17
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Larry's reply to the OP is backward. If the back of the bike is lower, less tankslapper, more straight line stability.
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Old 06-16-2013, 10:08 AM   #18
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Originally Posted by corndog67 View Post
Larry's reply to the OP is backward. If the back of the bike is lower, less tankslapper, more straight line stability.
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Old 06-17-2013, 10:18 AM   #19
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Quote:
Originally Posted by corndog67 View Post
Larry's reply to the OP is backward. If the back of the bike is lower, less tankslapper, more straight line stability.
To a point. Eventually, (especially with heavy luggage hanging out in a top box), the geometry gets so relaxed, that normal gyroscopic procession doesn't function right anymore and the bike goes into a weave -- it literally can't hold itself up anymore. That's why I was saying it's not really a "tank slapper" per se...

BTW, tank slappers often happen when a n00b rider hammers the throttle WFO, and hangs on to the bars tightly, while all the weight goes to the rear wheel. The front tire can't do it's think right anymore, and goes all over the place.
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Old 06-17-2013, 12:35 PM   #20
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And the front-end shimmy/wobble may be the bike telling you to check the head bearings, wheel bearings and swingarm bearings. Above and beyond the rear flat and the uber-loaded topbox.

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Old 06-17-2013, 03:19 PM   #21
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Originally Posted by stefer View Post
I can see this, but would changing the angle by an
inch or two make that much of a difference in handling?.
Think of it this way when you adjust the height of the front forks it is measured in MM's.

A flat tire will cause a sudden change measured in inches.
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Old 06-18-2013, 08:24 AM   #22
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Experiments with rake and trail variations:

http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

Why high aft weights are bad for steering:

http://www.tonyfoale.com/book/Geom2.PDF

lnewqban screwed with this post 06-18-2013 at 08:41 AM
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Old 06-18-2013, 04:06 PM   #23
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Thanks everyone for your contributions. I think I'll pick up David Houge's book and try to clear up some misconceptions in my head. That book lnewgban posted looks amazing, but there isn't enough time in the day for me to do that book justice. Any of you engineering types interested in motorcycle dynamics give that book a look -- it looks phenomenal.

Got the new tire on and shes up and running again. Took the wheel over to the dealer as my tire irons are missing and my flat head screwdrivers wern't getting it done -- so I'm not sure what caused the flat.

As for bearings Bill Harris, the bike has 8k miles on it, mostly street...but I guess it only takes a little bit of contamination to cause rapid wear. I haven't noticed any symptoms but I'll look into getting sealed bearings because I know I can get em pretty cheap and have wanted to do that for quite some time anyways.

Thanks again everyone.
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Old 06-18-2013, 04:09 PM   #24
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Quote:
Originally Posted by larryboy View Post
Rear flat tire drops the back of the back of the bike which increases the rake and trail of the front end...hold on, it's tank slapper time.
yup, you might get lucky and lean over the bars to help it out, IF you react in time
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Old 06-18-2013, 09:11 PM   #25
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If you go fast enough , the tire stands up on it's own from the centrifugal force.
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