Sudden tank-slappers! - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 28 Old 09-21-2009, 05:01 PM Thread Starter
ZAR
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Sudden tank-slappers!

Saturday I almost had a big fall. It was the third time this happened to me but this was the closest to biting the dirt yet!

I was riding at about 80km/h on a corrugated dirt road when suddenly and without warning the handles started to dance. Like full tank-slappers. I still donít know what I did not to fall but I almost shat myself.

Every time it happened was on a corrugated dirt road. Anyone here know why it happens and what to do to avoid it?

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post #2 of 28 Old 09-21-2009, 05:13 PM
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Slow down a bit?
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post #3 of 28 Old 09-21-2009, 05:18 PM
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Slower will help. So will a Scotts steering stabilizer.

Pat- 2007 DL650A was ridden to all 48 contiguous states. I didn't quite make it to 17,000 miles on the 2012 DL650A.
Nicknames I use to lessen typing, Vee = 2002-2012 DL1000s. Vee2=2014-2016 DL1000s. Wee = 2004-2011 DL650s. Glee = 2012-2016 DL650s
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post #4 of 28 Old 09-21-2009, 05:31 PM
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I have nothing meaningfull to contribute as to why this happened, but I'm curious about low-speed waggles. I've only heard of ones that are when the hands are off the bars, usually when the tires are fairly worn, and accentuated when there is a heavier than normal load on the back of the bike.

Did the action end imediately when you firmed up your grip on the bars or did you have to really struggle to stop the front end motion?

Was the front lightly loaded at the time (as would happen when going up a steep hill) or the back heavily loaded?

Were you off the throttle, on it, or fairly neutral on the throttle?

..Tom

2006 DL650: 202,000 km 125,500 miles, Sold
2012 DL650 139,500+ km, 86,700+ miles. Sold
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post #5 of 28 Old 09-21-2009, 05:44 PM
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On my bike, I did 108 mph the other day on an open road and while slowing down it began to wobble to almost tank slap. Scary to say the least.

While accelerating it was as steady as a rock. I know that does not help but is my experience.

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post #6 of 28 Old 09-21-2009, 05:47 PM
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dont hold onto the bars so tight , i have hit 160klmph hour on dirt roads with out any tank slap . relax your hold on the bars . i find 140 klm a good speed on logging roads . 120 klm if the road is bad

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post #7 of 28 Old 09-21-2009, 06:18 PM
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You need more weight in the front. Raise your spring preload in the rear and/or raise your forks in a bit in your triple clamps.

Thats the cheap free way.

A steering dampner is great also.. but spendy.

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post #8 of 28 Old 09-21-2009, 06:47 PM
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Weight on the front

[QUOTE=Gravehunter;466827]You need more weight in the front.

My Wee has been very stable. I do pay extra attention passing double semis, car carriers and fast running long nose trucks on interstates during hard side winds. This is out west running 80-90 mph (actual) fully loaded. A brand new rear tire makes it a little worse and it mostly goes away when center tread gets flattened.

When I'm approaching one of the above, I lean forward over the tank, getting more weight on the front, and accelerate through the truck turbulence. Works pretty well.


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post #9 of 28 Old 09-21-2009, 08:18 PM
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Floppy

The forks and frame are a little floppy, relative to modern frame design. As such it is easy to get the whole system oscillating. If you've never ridden dirt bikes, it is easy to over-correct the steering when things start moving around. Relax and let the bike move around a little, and you won't have the problem. A fork brace may help.
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post #10 of 28 Old 09-21-2009, 08:35 PM
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Quote:
Originally Posted by ZAR View Post
I was riding at about 80km/h (50 mph) on a corrugated dirt road when suddenly and without warning the handles started to dance. Like full tank-slappers.

Every time it happened was on a corrugated dirt road. Anyone here know why it happens and what to do to avoid it?
Does this link relate to what you experienced?
http://www.msgroup.org/Tip.aspx?Num=164&Set=
"Trail is the distance between the middle of your contact patch and that point on the ground pointed to by an imaginary line running through your steering stem. It is created as a result of rake angle, offset and tire radius. Because of trail your tire develops a restoring force that attempts to keep your front-end pointing straight ahead. The longer the trail is, the stronger this force is. The heavier your front-end is, the stronger this force is (when braking, for example.)

"... a front tire is about to run over an object on the ground simulating a raised RR track or an unusually harsh speed bump. What is important to note is that at the moment of contact between your tire and that bump your contact patch will be lifted off the ground (to be replaced by the tire riding on the bump) and at that time your tire will have created a NEGATIVE trail. In other words, at that time your steering axis will be behind your contact patch. (ALL bumps shorten your trail or turn it negative.)

"if your front wheel was pointing off at any meaningful angle when you hit it (you are in a turn) a totally unexpected thing happens - the negative trail, instead of trying to correct an off-center rolling direction, will try to accentuate that off-center direction. In other words, in the blink of an eye you will find that your front tire tries to make the turn TIGHTER! The subsequent reversal of trail to positive again is so strong a change that unless your steering head damper is working properly you can end up in a wild side-to-side tank slapper fight with your handlebars and possibly end up on the ground.

"One more thing, if you hit a second bump, as you will in the case of a RR track, and if that happens in almost the same interval of time that it has taken you to recover from the first bump, unless your steering damper is properly adjusted, you will experience a PROFOUND increase in loss of control!!!! This, because you will be causing an 'in phase' reinforcement - that is, you will have happened to 'tune in' to the dynamics of your front-end. {This is the real reason for a steering damper - to disrupt any rhythms ('de-tune') that could cause a pendulum effect on your front-end.}

"Clearly the message here is to always attempt to have your front-end pointing dead ahead when you are about to hit an obstacle, and always be sure that your front-end damping system is properly maintained. Further, if possible, stay off your brakes in this situation."

So...hit the corrugations straight on and install a steering damper. And hang on, but with a loose, flexible grip and body.
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