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Hey, all. Just joined the group as a new (used '09) Wee owner, but been riding 45+ years on a variety of moto-scoots. My last bike was a '95 Kaw GPZ1100. Sold it and bought the WeeStrom recently. On both bikes, I would occasionally have the oft-mentioned bar wobble with hands-off deceleration. Now, I'm not gonna argue that there prolly isn't a great reason to take my/your hands off the bar in this situation. However, there are also a significant number of posts on many different MC forums about this phenomenon with not much agreement as to whether it's a tire issue, wheel balance issue, loose/worn steering stem bearings, worn swing arm bushings, etc.

I have an observation (n=2) and a question for the forum. When I have experienced this--and it has happened at different times during my bike ownership including immediately AFTER changing tires and/or chain adjustment--I have been very successful at eliminating the problem by rechecking the rear wheel alignment and recentering the wheel. I did this by using a straight edge and aligning the tire very exactly to a centerline reference point on the bike frame, rather than using the hash marks on the swingarm. Bike(s) ran straight and true without wobble after the alignment.

Hands-off riding--all of us have to remember doing the same thing on our ancient American Flyers as kids, right? I came to this diagnosis because, when I would take my hands off the bars and try to balance the bike in a straight line, I would have to hold an uneven body position (weighted to one side) in the saddle to make the bike track straight. I know for a fact that neither bike was wrecked or had frame damage, so it has to be a rear tire alignment, IMHO.

If you have this issue on one of your bikes, see if your can track a straight line with hands off the bar and sitting straight in the saddle. If not, check/adjust your rear tire alignment and see if it doesn't fix the problem. PLEASE NOTE: Don't ride no-hands if you don't have the skill set to do so without wrecking--I'm not advocating reckless riding!

So, my question is: Does this make sense to anyone? Has anyone else noticed this issue and attempted to cure it? What are the physics involved that would cause a bar wobble due to rear tire misalignment?

GreyWolf, R U listening?
 

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I experienced this recently, under very similar circumstances (new-to-me '09) after lowering the bike. I adjusted the chain afterwards and lined up the marks carefull. Have not noticed it since.

FYI I had an old '79 GoldWing that I bought used some years ago. I noticed that it would fall into turns in one direction, but resisted in the other, and did not want to go straight at very low speeds.

I diagnosed it by taking one of those cheap carpentry lasers (that project a straight line) and positioned it so that it was projected down the bead of the rear tire (touching uniformly along the tire casing on one side). I then marked where the laser fell on the ground beside the front tire. I did this on both sides, and was able to determine that the steering head had been tweaked to one side.

If you do this on a relatively flat surface (level concrete garage floor) looking at both sides of the rear tire, then you can (by difference) figure out where it is pointing relative to the front tire and correct it. It doesn't matter that the front tire is a different width. By marking on either side of the front tire on the floor, you can get a sence of whether the front tire is centered between the marks.

P.S. I also loosened the front axle pinch bolt and compressed the forks a few times, to make sure that I had recentered the front wheel after lowering the front end.
 

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However, there are also a significant number of posts on many different MC forums about this phenomenon with not much agreement as to whether it's a tire issue, wheel balance issue, loose/worn steering stem bearings, worn swing arm bushings, etc.
There is no agreement because any of those can be an issue. Each individual bike needs to have the cause(es) checked. The top causes are tires and loose steering head bearings. What is your front tire brand and model? How many miles does it have on it? If you prop the front tire off the ground, can any movement be detected when putting force on the upper fork tubes other than axial around the steering head? Does pushing a handlebar grip toward the back of the bike with the front wheel propped off the ground in line with the bike's center line using the nail on a pinky finger start the handlebar moving without flexing the first joint of the finger?
 

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What Kinda Bike Is That?
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Has anyone else noticed this issue and attempted to cure it?
Recently, this topic has come up several times; mentioned by different riders.

There is a "Google Search Dialog Box" at the top of this page. Type into that box, "Decel Wobble", or just plain "Wobble", and you will see several threads and posts on the topic.

I cured the wobble on my bike by installing tapered roller, stem head bearings.


B.L.
 

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I believe the OP already is aware of the many threads on this topic. Rather than asking what causes it, he is asking if others have experience with one specific possible cause -- rear wheel misalignment.

I don't have anything to add about that particular issue, but I'll definitely be checking it soon as my chain is about due for an adjustment, and I'm seeing the decel wobble (though it might be due to front tire wear).
 

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FORUM GODFATHER.....R.I.P. PAT
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A rear wheel misalignment will normally cause a bike to veer to one side when the bars are released rather than wobble.
 

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What Kinda Bike Is That?
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Hands-off riding--all of us have to remember doing the same thing on our ancient American Flyers as kids, right? I came to this diagnosis because, when I would take my hands off the bars and try to balance the bike in a straight line, I would have to hold an uneven body position (weighted to one side) in the saddle to make the bike track straight. I know for a fact that neither bike was wrecked or had frame damage, so it has to be a rear tire alignment, IMHO.
As far as I know of, every road has a crown engineered into it so that water drains off of its surface. Secondary roads often have, or are perceived to have larger crowns, (at least here in New England they do!).

The crown in a road can cause you to incur a "weighted to one side" body position. It will also wear your tires unevenly.

B.L.
 

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What Kinda Bike Is That?
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I believe the OP already is aware of the many threads on this topic. Rather than asking what causes it, he is asking if others have experience with one specific possible cause -- rear wheel misalignment.

I don't have anything to add about that particular issue, but I'll definitely be checking it soon as my chain is about due for an adjustment, and I'm seeing the decel wobble (though it might be due to front tire wear).
So noted. Thanks.
 

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The crown in a road can cause you to incur a "weighted to one side" body position. It will also wear your tires unevenly.
BL, I'm not actually trying to contradict you at every turn. But it's my understanding that road crowns are not extreme enough to cause the uneven tire wear many see on motorcycles. Rather it's the fact that due to the way intersections are laid out, bikes actually travel farther (at least twice as far per intersection, depending on the size of the road) turning left than they do turning right. Over time this produces more wear on the left side of the tires. Obviously riders in countries that drive on the left side of the road see more wear on the right side of the tires.

If we need to discuss further, let's start a new thread to avoid hijacking this one.
 

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What Kinda Bike Is That?
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BL, I'm not actually trying to contradict you at every turn. But it's my understanding that road crowns are not extreme enough to cause the uneven tire wear many see on motorcycles. Rather it's the fact that due to the way intersections are laid out, bikes actually travel farther (at least twice as far per intersection, depending on the size of the road) turning left than they do turning right. Over time this produces more wear on the left side of the tires. Obviously riders in countries that drive on the left side of the road see more wear on the right side of the tires.

If we need to discuss further, let's start a new thread to avoid hijacking this one.
Please visit me in Maine. The "Crown" jewel of New England!
 

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Discussion Starter #11 (Edited)
There is no agreement because any of those can be an issue. Each individual bike needs to have the cause(es) checked. The top causes are tires and loose steering head bearings. What is your front tire brand and model? How many miles does it have on it? If you prop the front tire off the ground, can any movement be detected when putting force on the upper fork tubes other than axial around the steering head? Does pushing a handlebar grip toward the back of the bike with the front wheel propped off the ground in line with the bike's center line using the nail on a pinky finger start the handlebar moving without flexing the first joint of the finger?
GW: I'm well aware of the link to loose/worn steering stem bearings. I've done many rounds of tightening, replacement, and in particular, the upgrade from balls to tapered rollers. That's not the case with the Wee, nor was it the case for the GPZ. I suspect that there are some bikes whose design/frame geometry/weight distribution makes them more susceptible to instability than other bikes.

You can easily observe the alignment problems this causes in cars with the rear axle out of alignment (thrust alignment), usually due to broken rear locater pins on the axle as a result of collision. Seems like the same physics would apply to MCs.

In my case, the front tire has over 10K on it and is indeed due for replacement. What I noticed, though, was that I could reduce or eliminate the wobble by a more exact rear wheel alignment. I agree that all potential causes should be examined and checked. I was merely asking if any other riders had played with rear tire alignment and found it to make a difference.

Now that I've asked the question, I may be forced to be scientifically rigorous and do the definitive experiment: purposely mis-align my rear tire to varying degrees and see what effect it has on stability and riding feel. If I get a few days of free time, I'll do this and report back....assuming I survive the experiment!
 

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Steering oscillation (aka wobble) has a few potential root causes. All of them are related to the rotating mass of the front (or more rarely rear) wheel. Those would be a misbalanced wheel, a non-true wheel, or a tire that has worn (or was manufactured) unevenly.

A bike's front end geometry, its trail and rake (aka caster) will make a bike more or less stable, or conversely less or more sensitive to the (normally small) oscillatory inputs that are always present on a bike. When those inputs become larger than the inherent steering stability can dampen, you get the wobbles.

Having a misaligned rear wheel should not really be a cause of front end oscillation, unless somehow by having the tire canted on an angle to the direction of travel the tread blocks then impart some added stimulation into the frame.

Also, FWIW, oscillation can not be caused by the steering head bearings. But it can definitely be masked or "cured" by increasing the head bearing's resistance to turn, either by increasing the bearing pre-load or by switching to the tapered roller type of bearings. Either of those will have the mechanical effect of a steering stabilizer on damping the oscillations.
 

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Discussion Starter #13 (Edited)
Aha! An engineer weighs in on the question....

I think I understand the issue and what you have stated and I agree...in theory. However, one additional question (hopefully, this doesn't sound idiotic and relegate me to the staus of "Stupid Question Guy"):

When I think about the problem of a bar wobble, I agree with you that front wheel/tire imbalance can cause the problem, and that all the other factors mentioned are merely adding to the severity of the symptoms. However, the factor of wind pressure has never been discussed, and it seems to me that it could easily be causitive as well.

I think of the examples of a stream and how it flows in a winding path, or a flag waving as a result of flow dynamics. Could the same flow phenomenon cause the rythmic precession of the bars as function of the bike/rider position and the rear tire alignment?

OK, I know I'm getting a little too anally retentive with this whole issue, and I should just go ride! I'll bow out now and say thanks for the discussion before I get flamed for asking MORE dumb questions....
 

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...So, my question is: Does this make sense to anyone? Has anyone else noticed this issue and attempted to cure it? What are the physics involved that would cause a bar wobble due to rear tire misalignment?
..
My suspicion is that this is the root of the issue and everything else just contributes in a positive or negative way. I have said so in the past and have found that little changes in rear wheel alignment can make the issue a bit better or worse.

Here are my thoughts about it:

A minor misalignment causes a slight sideways pull on the front tire.

The Caster and trail in the front causes the wheel to naturally correct by turning the front wheel a bit and follow the direction of travel.

The front wheel has mass and inertia causes it to move slightly past the point at which the forces would balance.

Now the wheel needs to move back a bit to compensate for the over-reaction of the front wheel. The wheel starts moving back, crosses the balance point and the cycle repeats.

So why do tires matter?

-Tires with profiles that are more rounded cause more side forces so tend to increase the sideways pull of the tire that starts the oscillation. Notice that when tires wear they get flatter and the effect increases as there is more rubber contacting on the side.

-Tires that are more "V" shaped tend to put rubber towards the center of the track so there is less sideways pulling.

-Tire pressure also has an effect on the effective shape of the tire and can make a difference as well.

Why does steering head bearing tightness matter?

-tighter steering head bearings can provide more "damping" that slows down the ability of the wheel to pass the balance point when encountering uneven forces. This helps stop the initial oscillation.

Why does loading the back of the bike more make this worse?

-less weight on the front wheel can reduce the ability of the trail in the tire to keep it pointing straight but doesn't lessen the side forces as much (?) or less weight on the front helps the steering bearing to move more freely (?)

Why does this happen only at certain speeds?

-oscillations tend to react at certain frequencies. Likely to combination of the trail, the weight of the bike, etc. cause some positive feedback the reinforces the little oscillation that starts it all

How is this different than a "Speed Wobble"

-Speed wobbles are related but tend to be higher speed phenomena and generally overpower the ability of the rider to stop the bars from shaking, leading to the "Tank Slapper"

-The low speed wobble (or Waggle or weeble or whatever) dampens quite easily by simply holding the handlebars.

Why does this happen more when slowing down?

-A bit of weight shift to the front can load the front tires and cause the tire to flatten a bit.

..Tom
 

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Aha! An engineer weighs in on the question....

I think I understand the issue and what you have stated and I agree...in theory. However, one additional question (hopefully, this doesn't sound idiotic and relegate me to the staus of "Stupid Question Guy"):

When I think about the problem of a bar wobble, I agree with you that front wheel/tire imbalance can cause the problem, and that all the other factors mentioned are merely adding to the severity of the symptoms. However, the factor of wind pressure has never been discussed, and it seems to me that it could easily be causitive as well.
Sorry, yes, you are quite right. Air turbulence is another place the chassis can receive oscillatory stimulus from. In fact, this is very common complaint, usually occurring primarily at higher road (and therefore air) speeds and with added accessories like rear travel trunks, etc.

But it isn't typically related to having your hands on the bars. The weaving and wobbling due to aerodynamics will often happen with both hands on the bars, but at speeds over 90 mph.
 

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Hope this doesn't constitute a thread highjack, but I'm compelled to ask this with the current audience participating.

Motorcycle wheel balancing ...... When a professional , (a dealer for example), does it ... does their machine tell them on which SIDE of the rim to add a weight? Or do they clip the weight to the rib running down the center of the rim?

I ask because car wheel rim widths are measured and put into the calculation to determine needed weight. The worker's directed to put X amount of weight on a spot AND specifically on which side of the rim.

I think you all know what I''m getting at here. I mean is a m/c wheel wide enough to BENEFIT from a balance job specifying a weight be added a a spot AND a certasin distance from the rims centerline?

I mount my tires and do a static balance job. This method however never will be able to correct for an imbalance off centerline. This can only be tracked, (and corrections made for), by a balancer measuring the forces a wobbling wheel is putting on the machines spindle (or what evr it's called).

dave
 

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I had this problem at first on my wee. Checked the tire pressure. I was about 5 pounds low. So I adjusted the pressures to the proper levels and it went away. YMMV
 

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Steering oscillation (aka wobble) has a few potential root causes. All of them are related to the rotating mass of the front (or more rarely rear) wheel. Those would be a misbalanced wheel, a non-true wheel, or a tire that has worn (or was manufactured) unevenly.

A bike's front end geometry, its trail and rake (aka caster) will make a bike more or less stable, or conversely less or more sensitive to the (normally small) oscillatory inputs that are always present on a bike. When those inputs become larger than the inherent steering stability can dampen, you get the wobbles.

Having a misaligned rear wheel should not really be a cause of front end oscillation, unless somehow by having the tire canted on an angle to the direction of travel the tread blocks then impart some added stimulation into the frame.

Also, FWIW, oscillation can not be caused by the steering head bearings. But it can definitely be masked or "cured" by increasing the head bearing's resistance to turn, either by increasing the bearing pre-load or by switching to the tapered roller type of bearings. Either of those will have the mechanical effect of a steering stabilizer on damping the oscillations.
Thanks for explaining things in a way I seem incapable of.
The steering head bearing guru's should be along shortly to set you straight.
 

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FORUM GODFATHER.....R.I.P. PAT
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A too loose steering head bearing will cause a wobble and too tight will cause a weave. Ask anybody who has found both sides of the action when adjusting a steering head. The rake and trail self centering action will over react quickly if loose and too slowly if tight. Only a proper setup will allow tracking close enough the the selected line to be problem free.
 

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Hope this doesn't constitute a thread highjack, but I'm compelled to ask this with the current audience participating.

Motorcycle wheel balancing ...... When a professional , (a dealer for example), does it ... does their machine tell them on which SIDE of the rim to add a weight? Or do they clip the weight to the rib running down the center of the rim?
A bike wheel (specifically the tire) is not really wide enough for the side to side tolerances in weight to be significant, the way that it can be on auto wheels. We also mount our wheels "on center", where most car wheels have an offset.

That said, if you did have an abnormally large, lateral imbalance on a MC wheel it would be pretty hard to compensate for, since the inner rim surface is not very wide. It's one thing that does come to mind when using car tires on the back of motos. You'd want to use tires of the best possible original balance.
 
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