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High-speed extreme wobble

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Any time I go over 85 (indicated) on my SM, the bike starts to wobble madly. It's not a tank-slapper, the whole bike is going back and forth, and letting off the throttle and slowing down makes it go away.

It doesn't build to the wobble, either, the bike seems to go straight from rock-steady to "yer fooked, d00d!" in seconds. 👍 I can replicate it, and it always kicks in as I pass 85.

The Zed didn't do this last year. I haven't changed anything on the bike, except fiddling the jetting.

Last summer, I had stiffer springs put in the front forks by a shop, and replaced the rear spring myself with a stiffer one. I rode two track days and had no problems with the suspension.

But, when I had the suspension done, I was 285 lbs. After some rather frightening results from blood work last fall, I'm down to 260 lbs.

Could the weight difference be causing the high-speed, yer-gonna-die wobble? Getting way out over the bars seems to help damp it, but I have no idea what my speed is like that, so I may just be sail-braking.

I haven't checked the sag, but presumably the rear pre-load needs to be lightened. Is that going to help this problem? Make it worse? Do nothing?

Any input appreciated. I might be doing a track day this weekend, and I'd hate to throw the bike down the straight-away.🤣

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maybe you can try rising the forks in the clamps (effectively lowering the front). This would transfer more weight to the forks and may cure the wobble. Make sure to pump the forks a few times when you replace the wheel to align the axle before torquing the pinch bolts

My 2c

👍

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Start by checking tires for wear and pressure. Also, make sure wheel weights are all there so its balanced.

25 pounds should not make too much of a difference.

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The fact that it hits at a specific speed to me indicates the tire is out of balance. I had an issue with an oscilation that would I could feel go side to side and front to back that turned out to be a tire just slightly out of balance in the rear that would only appear when I hit 75+mph. Fixing that and swapping out the front fender has me rock solid up to 90mph. Does sitting further forward or back on the bike make a difference? Do your head bearings have any play?

Or of course it could be that you have found the resonant frequency of the bike and your new fatter self.👍

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Or of course it could be that you have found the resonant frequency of the bike and your new fatter self.

Read my post again. 👍, indeed.

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These can be tough.....but I would say right off that the 25lbs prob isn't coming into play (it'll help with your power-to-weight ratio for sure tho!).

So now you have to run thru the troubleshooting process of elimination...

Wheels properly inflated?

Wheels properly balanced?

Spokes properly tightened?

Head bearings tight and without play?

Is the rear set up? Rear tire all checked out? Rear shock as well?

Just gotta run down a check list item by item till you nail it. Congrats on the weight loss, and good luck with the bike!

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Double ditto on proper wheel balance, especially so if you are running single rim-locks.

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Double ditto on proper wheel balance, especially so if you are running single rim-locks.

SM wheels do not have rim locks.

And folks, please don't say that IT IS the "stock" front fender again.👍

My guess would be your weight difference, and the stiffer springs. Definitely set the sag properly 1st. And ditto on the wheel balance.

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I had wobble when i was riding over 100 km/h ( with rm 250 fender and no handguards)

When i changed to Polisport Exura fender og put on a pair of cycra hand guards the wobble was gone ;O

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My bike does not have any wobble...but I can induce some by sqeezing the bars with a death grip. Also seems like I can affect it by changing my position on the seat just a bit.

Relax your grip and try some different positions forward and back on the seat.

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I am going with tires on this one. does the road surface you rode have rain grooves?

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And folks, please don't say that IT IS the "stock" front fender again.

Moot point--I've got an Acerbis on the bike. I'm reading everyone else's comments, too. Thanks for the input.

I ended up getting hacked at the carb so I ripped it off the bike and decided to re-check the valve clearances while I had 'er in pieces anyway.

I'll report back what I figure out once I get back on the road. 👍

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