Low Speed Death Wobble

[Fat Jeff]

My '19 GT had done the odd low speed wobble at approx 20 km/hr a few times last month.  I upped the front tire pressure from 33 to 36 psi a few weeks back and today it happened about half a dozen times on one stretch of road while slowly accelerating...it was so bad the bike almost went out of control, I hit the clutch and let the bike slow down and when it is barely moving the wobble goes away.  The road was a bit rough, but all Alberta roads are rough so nothing different there.

I was a bit concerned once I hit the hwy to get home but it was fine, only seemed to do it at low speeds...checked the tires again this evening, still at 36 front and rear, no play in the steering or wheel bearings and I didn't have the bike loaded.  Nothing has changed on the bike either, so this has me puzzled...it has 3000km and the stock tires...and even though my nickname is Fat Jeff, I'm a fit 165lbs.

I haven't touched the suspension since I adjusted it a year ago, it's all stock, tires have no sign of abnormal wear, and chain slack is within spec.

Any thoughts?

[betoney]

15 minutes ago, Fat Jeff said:

My '19 GT had done the odd low speed wobble at approx 20 km/hr a few times last month.  I upped the front tire pressure from 33 to 36 psi a few weeks back and today it happened about half a dozen times on one stretch of road while slowly accelerating...it was so bad the bike almost went out of control,

That's only 12mph, I cant imagine anything causing it to wobble so bad that you almost lose control riding that slow... Usually when people report a speed wobble it happens at 10x that speed.

So no changes or maintenance performed?, the bike was 100% fine and then it started shaking out of the blue?

[Fat Jeff]

Yep, it did it a coupe of times last month but only when I hit a rough patch of road so I wasn't too concerned but did up the front tire pressure by 3psi.

Nothing has changed...seems to be lots of people complaining about it when searching the great google, but no real cause or cure.

[Dodgy Knees]

Strange...have a good look at tyre fitting, bulges etc or maybe brake binding on one side.??  Never heard of this before. 

[Buggy Nate]

Just making sure you aren’t doing anything silly like taking your hands off the handle bars are you?

We used to get so many customers come in and say my bike wobbles when I take my hands off the bars.

Id say ‘don’t do that then’.

[TTR Ignition]

Try dropping the front pressure back down to 33psi.

[1moreroad]

Put it up on the center stand with weight on the back end.  Make sure the handlebars turn cleanly and smoothly from side to side.  Spin the front wheel by hand and look for hops and brake drag.  If it's happening at 12 mph, you should be able to spin the wheel up to that speed for at least a few seconds.  Spin the back wheel, too, in case there's something back there that's causing a hop.

[koth442]

Sounds like a wheel is misaligned or something in the drive train is loose. Could be front OR rear. How's your rear tire pressure? 

[Shizzle]

Steering stem nut could be a possibility

[betoney]

8 hours ago, Fat Jeff said:

seems to be lots of people complaining about it when searching the great google, but no real cause or cure.

But those search results are for HIGH SPEED wobble, which is more understandable. 

Other than the severe shaking, does the bike feel and sound normal?  If you were to ride down the road and make big swerves side to side is everything smooth?  If you accelerate and brake in stoplight to stoplight type riding is there any abnormal noise and does it track in a straight line?

[Fat Jeff]

Thanks for the replies, and nope, never take my hands off the bars!  If you google low speed wobble or tank slapper, there is plenty on the web. I did check both front and rear in case something was misaligned, checked all fasteners and all is good.  Front and rear tires are both at 36psi.  Other than that wobble, everything was fine, I was a bit nervous coming home when crossing the Railway tracks at hwy speed as it’s a fair bump but the bike had no issues. 

One thing I recalled this morning was the first mod I added were anti vibration bar risers so I double checked the risers and was able to tighten the anti vibration bolts A full turn...not sure if that will help until I hit the city for a test ride down that same road. 

[Stew]

Front wheel missing any balance weights? Front tyre squared off? Front wheel bearing shot? Steering head too tight or loose?

The only time I ever had anything even vaguely like that was with dried out and seized head bearings on an old GS550 that I bought 2nd hand.

[betoney]

4 minutes ago, Fat Jeff said:

One thing I recalled this morning was the first mod I added were anti vibration bar risers so I double checked the risers and was able to tighten the anti vibration bolts A full turn...not sure if that will help until I hit the city for a test ride down that same road. 

Hopefully tightening the bolts is the solution.

When you say "test ride down that same road", was this only happening on a certain section of road? 

[Fat Jeff]

It was fine all over town yesterday, then on the way home on the last stretch of road it kept doing it over and over, prob half a dozen times. The pavement was a bit rough, but no more so than the other roads. 
Bike only has 3000km, no play in steering bearing and it moves freely so not too tight. Wheel weight is there plus it was smooth on the hwy. 

I may hit town tomorrow and see if tightening the riser bolts helped. 

[Manxkiwi]

Sounds like a tough one to diagnose. I would check the wheel alignment next. With string or straight edges, don't trust the swingarm marks and don't think it's necessarily bang on from the factory. Having checked all you have already, that's all I can think of. It will be interesting to see if the problem goes away as soon as you put new tyres on?!