Tankslapper Speed Wobble, Weave - Kawasaki KLR 650 Forum
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post #1 of 30 Old 07-19-2012, 01:28 PM Thread Starter
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Tankslapper Speed Wobble, Weave

SPEED WOBBLE. I need to figure out why this happened so I can make sure it doesn't happen again.
SITUATION: Riding out on camping trip, heavily loaded, fairly wide rear soft panniers clinched tight against a hard pannier rack, front tank side panniers probably 12 pounds each, tank bag 10-12 pounds, Duffel bag strapped to back top plate medium weight, brand new tires and heavy duty tubes inflated to 35psi(Kendra k270's), full 5 gal gas tank, I weigh 265 pounds, this is on a 1994 KLR 650 stock. Had a fender bag on front with tools in it.

On a long flat straightaway I accelerate fairly rapidly up to 80 MPH(thought something on Carb stuck thought I'd try this to clear it out). All of a sudden the bike starts violently shaking from side to side both front and back and was getting worse quickly. I let of the throttle gently and was able to ride it out, but at the time I was sure I was going down. I don't recall exactly but I may have let off the throttle out of the acceleration right before the wobble started.

Can you give me your experience with this and help me figure out why this happened?

Thanks,
T33
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post #2 of 30 Old 07-19-2012, 03:12 PM
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How "aggressive" of a front tire?

~Things work out best for those that make the best of the way things work out~
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post #3 of 30 Old 07-19-2012, 03:25 PM
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Quote:
Originally Posted by troutbum33 View Post
SPEED WOBBLE. I need to figure out why this happened so I can make sure it doesn't happen again.
SITUATION: Riding out on camping trip, heavily loaded, fairly wide rear soft panniers clinched tight against a hard pannier rack, front tank side panniers probably 12 pounds each, tank bag 10-12 pounds, Duffel bag strapped to back top plate medium weight, brand new tires and heavy duty tubes inflated to 35psi(Kendra k270's), full 5 gal gas tank, I weigh 265 pounds, this is on a 1994 KLR 650 stock. Had a fender bag on front with tools in it.

On a long flat straightaway I accelerate fairly rapidly up to 80 MPH(thought something on Carb stuck thought I'd try this to clear it out). All of a sudden the bike starts violently shaking from side to side both front and back and was getting worse quickly. I let of the throttle gently and was able to ride it out, but at the time I was sure I was going down. I don't recall exactly but I may have let off the throttle out of the acceleration right before the wobble started.

Can you give me your experience with this and help me figure out why this happened?

Thanks,
T33
Load imbalance that you happened to cause constructive oscillation at that speed.

Steering bearing is starting to fail.

Those are two guesses with the limited information
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post #4 of 30 Old 07-19-2012, 03:40 PM
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Congrats on surviving.

A, get rid of at least half the load on the tank. It's too much weight, too far forward causing the overly soft front end to ride even lower, steepening the head angle.
B, don't chop throttle, as the front will squat, steepening the head angle and further exaggerating the problem. If you can, slide back in the seat to unload the front and slacken the head angle.
C, clamp the knees on the tank HARD, and loosen up on the handlebars, the bike WANTS to go straight. In the aviation world, it's called PIO (Pilot Induced Oscillation). You are consciously or unconsciously trying to correct, and using too much input, which sets it off the other way.
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post #5 of 30 Old 07-19-2012, 04:22 PM
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Originally Posted by thetable View Post
Congrats on surviving.

A, get rid of at least half the load on the tank. It's too much weight, too far forward causing the overly soft front end to ride even lower, steepening the head angle.
B, don't chop throttle, as the front will squat, steepening the head angle and further exaggerating the problem. If you can, slide back in the seat to unload the front and slacken the head angle.
C, clamp the knees on the tank HARD, and loosen up on the handlebars, the bike WANTS to go straight. In the aviation world, it's called PIO (Pilot Induced Oscillation). You are consciously or unconsciously trying to correct, and using too much input, which sets it off the other way.
Thanks - good post. I experienced a mild episode of this in my first week of owning a KLR and wondered about this.
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post #6 of 30 Old 07-19-2012, 04:41 PM
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Similarly loaded it happened to me also, not bad but enough to scare the s**t out of me. Something about the geometry / suspension I can't define. I simply slow down loaded like that.
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post #7 of 30 Old 07-19-2012, 05:51 PM
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Stock syspension loaded down too much in the rear.

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post #8 of 30 Old 07-19-2012, 05:56 PM Thread Starter
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tire

Quote:
Originally Posted by masterlink View Post
How "aggressive" of a front tire?
Brand new Kenda k270 50/50 tire pretty knobby, same with rear, both at 35 psi.
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post #9 of 30 Old 07-19-2012, 06:09 PM Thread Starter
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weight forward

Quote:
Originally Posted by thetable View Post
Congrats on surviving.

A, get rid of at least half the load on the tank. It's too much weight, too far forward causing the overly soft front end to ride even lower, steepening the head angle.
B, don't chop throttle, as the front will squat, steepening the head angle and further exaggerating the problem. If you can, slide back in the seat to unload the front and slacken the head angle.
C, clamp the knees on the tank HARD, and loosen up on the handlebars, the bike WANTS to go straight. In the aviation world, it's called PIO (Pilot Induced Oscillation). You are consciously or unconsciously trying to correct, and using too much input, which sets it off the other way.
That's exactly opposite a lot of the advice I am getting. I was told tank bags were good to put weight forward so the bike isn't "butt heavy". And as far as moving back, the overwhelming majority says shift body forward and lower while loosening grip and slowly easing of the throttle.
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post #10 of 30 Old 07-19-2012, 07:26 PM Thread Starter
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Originally Posted by flash View Post
Similarly loaded it happened to me also, not bad but enough to scare the s**t out of me. Something about the geometry / suspension I can't define. I simply slow down loaded like that.
Yeah, I slowed down to 60 and under on the curvy mountain roads and had no problems the rest of the 425 miles that weekend.
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