A head-shake question or two

[Scab]

We've all read the gazillion head-shake threads where the problem is most often improper head torque or a tire balance issue. But I experienced something of late that has me wondering about some things that I do not have the answer for.

First, the basis:

2005 FJR

current mileage 24600

tires Strada's (since 22610 miles)

Here's the deal: Since installation of tires, bike has front fork oscillation. Not real bad, but noticeable. Previous tires handled VERY poorly and also displayed this condition.

I then ordered front wheel bearings and roller bearings for the steering head. They have yet to be installed.

This past weekend, I fabricated a spanner wrench for the head bearings. (in prep to install new bearings)

To test, I rechecked the bearing torque. Bearing torque was TOO TIGHT! (my mistake, from previous guesstimate)

I re-torqued with my fabricated tool and my new torque-o-matic.

Now, it gets interesting. The oscilation still exists, but now is very minute and at a much faster frequency.

So, here are some questions:

Can over-tightening of the steering bearings actually exagerate the oscilation? If this is possible, how? Does the additional pressure just add resistence that now makes the oscilation go to a more extreme position before it is countered by the caster force?

In determining causes for this condition, has the aerodynamic impact of V-strom handguard installation been considered?

In other words, could the addition of handguards cause/contribute to the oscilating effect? I do have handguards.

Or, do I just need to shut up and install the new bearings?

 

[Wingman]

To test, I rechecked the bearing torque. Bearing torque was TOO TIGHT! (my mistake, from previous guesstimate)I re-torqued with my fabricated tool and my new torque-o-matic.

Now, it gets interesting. The oscilation still exists, but now is very minute and at a much faster frequency.

So, here are some questions:

Can over-tightening of the steering bearings actually exagerate the oscilation? If this is possible, how? Does the additional pressure just add resistence that now makes the oscilation go to a more extreme position before it is countered by the caster force?

Your guess is as good as mine, but this theory seems plausible to me.

In determining causes for this condition, has the aerodynamic impact of V-strom handguard installation been considered?In other words, could the addition of handguards cause/contribute to the oscilating effect? I do have handguards.

The extra mass on the handlebars would probably tend to dampen the oscillations, but the extra wind resistance and possible turbulance could affect things negatively. You could remove them and go for a test ride. I doubt you will be able to tell any difference, but you never know.

I've always blamed uneven tire wear for the oscillations/headshake, but everything is connected and could be affecting the situation.

Or, do I just need to shut up and install the new bearings?

You're just asking for it with that question, but I'll be nice. :bleh: Install them, of course. . . and let us know how you like the new bearings.

David

 

[twowheelnut]

Scabby, just for ***** and giggles, raise your fork tubes in the triple tree by 1/8" - 1/4", so as to load the front end more. Test it and let me know if that helped.

 

[radman]

Can't say that I know enough about scooter chassis dynamics to answer the question involving the headstock bearings. I do know, however, that Frank has worn his handguards for thousands of miles with not a hint of headshake, including when the Azzaros were on. I do have a large windshield on (CB +4+4) which may alleviate the effect, the shieldwas on before the handguards. I have installed the roller headstock bearings, not due to any perceived problems with the originals, but to further solidify the front and provide maximum contact between the forks and the frame, which has been a good plan in the past. I would imagine the shake and the tire are connected (duh) and start by replacing it. The bearings certainly can't hurt. Other notables would be even mounting of the tubes in the trees, certainty that compression/rebound settings are equal side to side, and that weight over the tail be considered in the equation.

 

[Scab]

Scabby, just for ***** and giggles, raise your fork tubes in the triple tree by 1/8" - 1/4", so as to load the front end more. Test it and let me know if that helped.

Will do.

Can't say that I know enough about scooter chassis dynamics to answer the question involving the headstock bearings. I do know, however, that Frank has worn his handguards for thousands of miles with not a hint of headshake, including when the Azzaros were on. I do have a large windshield on (CB +4+4) which may alleviate the effect, the shieldwas on before the handguards. I have installed the roller headstock bearings, not due to any perceived problems with the originals, but to further solidify the front and provide maximum contact between the forks and the frame, which has been a good plan in the past. I would imagine the shake and the tire are connected (duh) and start by replacing it. The bearings certainly can't hurt. Other notables would be even mounting of the tubes in the trees, certainty that compression/rebound settings are equal side to side, and that weight over the tail be considered in the equation.

I will eliminate the 'removal of the handguards' experiment.

Front settings are equal. I usually have 'something' floating around in the bags, but nothing of any substantial weight. I have recently added a tailbag, but there was no difference noticed in 'before/after.' Rear stock shock is set to 'hard.' I can set to 'soft' and check also.

I am not knowledgeable enough about suspension settings to wander far in the adjustment woods. The preload is about all I have ever messed with and that was a year ago.

What really sent my mind down this rabbit hole is the difference after loosening the head bearings. Perhaps I have damaged the bearings with the "too much" previous torque.

 

[trimmantom]

Scab,This may not help at all but check the torgue settings on the lower pinch bolts also,if you haven't lowered the front end yet.

You're not still running 70 psi in those tires are you.LOL.

 

[rhody]

I had a similar experience with car tires not too long ago myself, slight front end oscillation at speeds in excess of 60 mph.

The answer was so simple I even missed it myself. As luck would have it I picked up a nail in a front tire, went in for a patch.

While the tech was rebalancing them he called me over, and said, "your two front POS tires are both not perfectly ROUND !!!

The solution while not practical for a motorcycle, but fine for a car, put the two new POS tires on the rear and swap the old rears for the front, (I said screw it, and put two quality tires on this time, no more POS's) which is what I did. As you stated in your post, they may only be slightly out of round, but I can guarantee that you will feel it when riding.

My were so far out of round it was obvious, maybe yours are just off enough to cause the oscillation. If you have the front taken off and carefully spun balanced, and pay careful attention to the tire for "bad juju" while on the spin balance machine.

Just a thought. :blink: If it turns out to be just the tire, you will save you a few bucks too.

 

[chornbe]

Scab, very timely.

I just took my V-Strom hand guards off and my weave-n-wobble front end settled down a LOT.

And yes, the bearings being too tight could have a damping effect and slow down the oscillation without removing it, thus causing a slower (leading to more pronounced) wobble. Actually makes perfect sense.

 

[v65]

for those that are smarter than I am

Pretty damn politically incorrect to rule out the lesser folks if you ask me

 

[Shane]

On other bikes, I have experienced front end anomalies related to bearings, both tension and detent related.

Too tight and the front will slowly weave (if you're lucky) and if it's really too tight, resist the self-correcting weave altogether in favor of the strange trip to the ditch while defying all known laws of countersteering.

Remember those tension knobs on top of the forks on vintage bikes, yeah, bad idea to make it so easy to just "crank 'er down" for "stability".

Also, bearings (usually ball-type) that have worn a detent pattern in the race will set up a strange weave-correct-weave-correct kind of thing that has to be felt to really appreciate.

The natural state of a motionless motorcycle is on it's side, so the front end will forever be in a state of course-correcting to remain upright while moving, each platform and setup potentially unique in feel.

Good luck,

Shane

 

[Scab]

Oh, you guys are good...

 

[charismaticmegafauna]

+1 on what TWN offered.

IME, it's the overall motorcycle attitude that contributes to this phenomenon -- that is, tail-draggin', weak rear suspension/overloaded rear. Biasing your bike more 'sportbike-like' tends to offset the condition. Both wheel and steering head bearings are long-lived m/c parts and usually only need replacing once in a long life of use (if at all?). Also, because it's the front wheel that manifests the ocillation, it's common to look there for the solution -- when, in fact, it can be caused from a problem at the rear of the bike: bad rear tire/insufficent pressure; poor/weak/improperly adjusted rear suspension; worn/loose swing arm bearings; overloaded rear/bike.

It may be part and parcel to the sport-touring conundrum....? :huh: