Tank slapper - Wrist Twisters
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post #1 of 18 Old 10-25-2017, 05:32 PM Thread Starter
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Tank slapper

My bars start to shimmy into what would eventually be a tank slapper when I remove my hands and decelerate at about 30 mph. It doesn't do this at speeds over 50. Im pretty sure it didn't do this before. The front tire down to the wear bars on the sides now that I've returned from deals gap. I just put on a 47 liter givi top case. My tire pressures were on the low side to build temp for the tail.

My plan is to reset the sag, increase tire pressure and eventually change the tires again, that's all I can really do. Has anyone else had this problem? I feel like something has to be really wrong to make the 919 so this. The bike definitely feels a little more rear biased on the weight, it wheelies pretty easy now...which I don't mind too much.


What's going on here?

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post #2 of 18 Old 10-25-2017, 07:18 PM
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Cupping on the front tyre.

I chased mine all over the place. The topcase made it worse for, so I was looking thru suspension and wheel bearing related stuff, but a new front tyre banished it completely and instantly. YMMV. but I'd do that first, and see if you have to do anything else afterwards...

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post #3 of 18 Old 10-25-2017, 07:19 PM Thread Starter
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My front tire does fit that description. I normally replace the front with the rear. I will replace it

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post #4 of 18 Old 10-26-2017, 05:48 AM
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I think it likely your front tire is primary cause and the rear top carrier is an aggravator.
Assuming a new front removes the primary cause, then the rear top carrier can't aggravate.

A heavy high rearward carrier is the absolute worst aggravator if something is going on re a chassis instability.

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post #5 of 18 Old 10-26-2017, 06:48 AM
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Ditto everything the other guys are saying... cupping is causing the problem, the topcase makes it worse... new tire and you'll be right as rain.

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post #6 of 18 Old 10-26-2017, 08:39 AM
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Same thing happened to me. I bought my 919 with 3600 miles on it. Still had the factory front tire and it was severely cupped. If i let go of the bars for just a second she would dance all over the place. New tire fixed the issue and I enjoyed riding her again.
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post #7 of 18 Old 10-26-2017, 08:00 PM
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What tires are you running? I had a Continental Road Attack front that would do that on my 919.

I swapped the front to a Michelin Pilot Power, and left the Continental RA on the rear. That was my favorite combination for the 919. I even did a track day with that combo.

I realize they're functional and all, but I can't imagine a high, rear mounted top case does anything but bad for the handling.

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post #8 of 18 Old 10-26-2017, 08:48 PM Thread Starter
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Quote:
Originally Posted by Sniper-x View Post
What tires are you running? I had a Continental Road Attack front that would do that on my 919.

I swapped the front to a Michelin Pilot Power, and left the Continental RA on the rear. That was my favorite combination for the 919. I even did a track day with that combo.

I realize they're functional and all, but I can't imagine a high, rear mounted top case does anything but bad for the handling.
Yep. Adds some heft to the bike for sure. But, I can always just remove the case if I want to do some spirited riding. I like having all the space though. Also makes wheelies really easy

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post #9 of 18 Old 10-27-2017, 03:45 AM
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post #10 of 18 Old 10-27-2017, 11:33 AM
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Bridgestone front tire by any chance?

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post #11 of 18 Old 10-27-2017, 12:15 PM Thread Starter
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Nope. Dunlop q3.

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post #12 of 18 Old 10-29-2017, 06:28 PM
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Just take a brick to it.

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post #13 of 18 Old 10-29-2017, 06:49 PM
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Quote:
Originally Posted by g00gl3it View Post
Just take a brick to it.
No that's for the rear tire. It's better to use sand on the front tire.

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post #14 of 18 Old 10-29-2017, 07:12 PM
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Quote:
Originally Posted by Pvster View Post
No that's for the rear tire. It's better to use sand on the front tire.
Hey, don't ruin it. I wanted a GoPro video of how to do this!!!

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post #15 of 18 Old 10-29-2017, 07:13 PM
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Quote:
Originally Posted by nathanktm View Post
My bars start to shimmy into what would eventually be a tank slapper when I remove my hands and decelerate at about 30 mph. It doesn't do this at speeds over 50. Im pretty sure it didn't do this before. The front tire down to the wear bars on the sides now that I've returned from deals gap. I just put on a 47 liter givi top case. My tire pressures were on the low side to build temp for the tail.

My plan is to reset the sag, increase tire pressure and eventually change the tires again, that's all I can really do. Has anyone else had this problem? I feel like something has to be really wrong to make the 919 so this. The bike definitely feels a little more rear biased on the weight, it wheelies pretty easy now...which I don't mind too much.


What's going on here?

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Nathan - just had the EXACT same thing happen after putting on my Givi top case and touring with it loaded up. Never had front end wobble before, but it started as soon as I put the top case on. Case goes off, wobble stops. I think it's an unavoidable side effect of a additional weight high and rearward - as well as additional drag which further shifts weight to the rear (and thus off the front wheel). Light front wheel = no resistance to its natural resonant wobbling frequency.

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post #16 of 18 Old 10-29-2017, 07:19 PM
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Quote:
Originally Posted by ST-DocLizard1 View Post
Time to watch Murray Walker: The discussion starts about 4:15.

https://www.youtube.com/watch?v=fvsDIq3WwVA
Didn't know a "lay down" was a solution. Interesting that just putting your head down makes that much difference.

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post #17 of 18 Old 10-29-2017, 07:24 PM
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Quote:
Originally Posted by LDH View Post
Bridgestone front tire by any chance?
Is there a problem with Bridgestone? I'm pretty sure some have recommended them.

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post #18 of 18 Old 10-30-2017, 08:52 AM
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Quote:
Originally Posted by KarlJay View Post
Is there a problem with Bridgestone? I'm pretty sure some have recommended them.

I wouldn't exactly call it a problem just more of a trait. Bridgestone front street tires have a really bad propensity for cupping problems. They also have a strange wandering feeling where they give the impression the front tire is following microgrooves on the road even though it's not actually moving around. I believe it has to do with the belting construction. I first started noticing it about 20 years ago with the BT56SS tires and I've experienced it still in more recent years with their modern tires.

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