'06 Front Wheel Oscillation

[Bustanut joker]

I concur.. It's the water in the carburetor..

 

[Fred W]

I lived with this head shake for the better part to 39 years, off and on. Recently I did the Penske and fork spring thing with fresh rubber and it reappeared. Started to think front end alignment.

Read on this forum where someone suggested that you tighten the front Axel pinch bolts with the fork tubes completely relaxed. That's where its at. This implies that the front end be jacked up. For 39 years I would compress the forks with the brake on and then with weight on the front tighten the pinch bolts. Hell I'd do this with single caliper front brakes. WRONG Now I compress the forks without the brake and then jack-up and go through the tightening sequence. The Gen2 shop manual goes through an elaborate description of how to tighten those pinch bolts.

Got $100 that says I can take that shake out of your front end in 10 minutes - don't care how loose your steering neck bearing are or how out of balance your tire is.

If I sound over excited, Remember it took me 39 years to get here.

Being a thinking man, I can't quite understand how what you say above can be true.

The root cause of head shake (especially at a specific road speed) has to be due to some rotating mass on the front end (wheel, tire, brake rotor). It can be mitigated (dampened out) by friction in the steering pivot, either a more restrictive steering head bearing like tapered rollers or by increasing the bearing preload or by adding dampening like with a steering stabilizer. It can also be lessened by relaxing the steering angles (rake and trail).

The solution that you propose to tighten the front axle pinch bolts with the suspension in a particular state will not effect any of the rotating mass, the steering pivot resistance or change the steering angles. I am not saying that what you have experienced does not have some validity, just curious how it could work. Can you explain how your proposal would do what you say it does?

 

[maddad]

Tires do not wear completely evenly because tires are not 100% completely even. They have a tread and along that tread or hib of the tread you'll get a little more wear. The older the tire gets, the more wear. Towards end of life you can feel it with your hand just by rubbing along the tire. We all call that scalloping. Low pressure will cause it to happen sooner. Most recommend running your tire at maximum rated pressure, unless you want it lower for a specific performance reason.

Biggest difference between PR2s and other tires is that PR2s have a symentrical tread pattern. They scallop as well but because the treads are matched on each site, the scalloping will match on each side. So with these ties, you don't tend to get the wabble, but rather later in the tire life, you get a little bit of vibration as the scalloping starts to have some impact.

 

[ionbeam]

...Started to think front end alignment...someone suggested that you tighten the front Axel pinch bolts with the fork tubes completely relaxed...Now I compress the forks without the brake and then jack-up and go through the tightening sequence...

...The root cause of head shake (especially at a specific road speed) has to be due to some rotating mass on the front end (wheel, tire, brake rotor). It can be mitigated (dampened out) by friction... It can also be lessened by relaxing the steering angles (rake and trail).

The solution that you propose to tighten the front axle pinch bolts with the suspension in a particular state will not effect any of the rotating mass, the steering pivot resistance or change the steering angles...

Note gumba stated alignment. Some motorcycles, especially in the past needed to have a procedure similar to what gumba states performed when reinstalling the front wheel. The procedure would typically request that the mechanic get the wheel installed but leave all the hardware finger tight; compress the front suspension,fully release the forks and tighten the front axle then the pinch bolts (if any). In theory this would align the fork lowers and wheels into a true vertical position and be square & centered with the frame. I have seen front wheels that were obviously not square and true corrected by this procedure.

What I don't know is how relevant this procedure is to the FJR's specific design and fork hardware. This procedure is typically used to correct pulling or handlebars that aren't squarely centered when the bike is going straight forward. Certainly the predominate root cause of the FJR's wobble is the front wheel initiating a resonance in the front end geometry. Some tread patterns or carcass designs may have harmonics that contribute to resonance right from new, other tires may get to this point when worn or tire pressure is wrong. As the winter grinds on I may be back to expand on this to include the things Mr W speaks about and how they may interact to cause steering resonance.

Wobble isn't necessarily a bad thing. If the steering was setup to prevent wobble in all cases, the steering would be too stiff and hard to turn. The lighter and more flickable the handling the more prone and sensitive it will be to wobble. The trick is to balance the instability so that it remains easily controllable, yet quick and responsive. Race bikes are setup to be inherently unstable for responsiveness, and then made controllable with a steering damper. Heck, the Air Force's most maneuverable planes are so unstable that they can't be flown by a human, they need a computer to keep the plane stable in the air.

Our FJR seems to be at the right place in terms of being on the verge of wobble yet it remains quite stable with any input from the rider. Many classes of motorcycles have the same handling and wobble characteristics as the FJR, especially the big heavy bikes that try to retain some semblance of sporty handling.

 

[gumba]

I lived with this head shake for the better part to 39 years, off and on. Recently I did the Penske and fork spring thing with fresh rubber and it reappeared. Started to think front end alignment.

Read on this forum where someone suggested that you tighten the front Axel pinch bolts with the fork tubes completely relaxed. That's where its at. This implies that the front end be jacked up. For 39 years I would compress the forks with the brake on and then with weight on the front tighten the pinch bolts. Hell I'd do this with single caliper front brakes. WRONG Now I compress the forks without the brake and then jack-up and go through the tightening sequence. The Gen2 shop manual goes through an elaborate description of how to tighten those pinch bolts.

Got $100 that says I can take that shake out of your front end in 10 minutes - don't care how loose your steering neck bearing are or how out of balance your tire is.

If I sound over excited, Remember it took me 39 years to get here.

Being a thinking man, I can't quite understand how what you say above can be true.

The root cause of head shake (especially at a specific road speed) has to be due to some rotating mass on the front end (wheel, tire, brake rotor). It can be mitigated (dampened out) by friction in the steering pivot, either a more restrictive steering head bearing like tapered rollers or by increasing the bearing preload or by adding dampening like with a steering stabilizer. It can also be lessened by relaxing the steering angles (rake and trail).

The solution that you propose to tighten the front axle pinch bolts with the suspension in a particular state will not effect any of the rotating mass, the steering pivot resistance or change the steering angles. I am not saying that what you have experienced does not have some validity, just curious how it could work. Can you explain how your proposal would do what you say it does?

 

[gumba]

I lived with this head shake for the better part to 39 years, off and on. Recently I did the Penske and fork spring thing with fresh rubber and it reappeared. Started to think front end alignment.

Read on this forum where someone suggested that you tighten the front Axel pinch bolts with the fork tubes completely relaxed. That's where its at. This implies that the front end be jacked up. For 39 years I would compress the forks with the brake on and then with weight on the front tighten the pinch bolts. Hell I'd do this with single caliper front brakes. WRONG Now I compress the forks without the brake and then jack-up and go through the tightening sequence. The Gen2 shop manual goes through an elaborate description of how to tighten those pinch bolts.

Got $100 that says I can take that shake out of your front end in 10 minutes - don't care how loose your steering neck bearing are or how out of balance your tire is.

If I sound over excited, Remember it took me 39 years to get here.

Being a thinking man, I can't quite understand how what you say above can be true.

The root cause of head shake (especially at a specific road speed) has to be due to some rotating mass on the front end (wheel, tire, brake rotor). It can be mitigated (dampened out) by friction in the steering pivot, either a more restrictive steering head bearing like tapered rollers or by increasing the bearing preload or by adding dampening like with a steering stabilizer. It can also be lessened by relaxing the steering angles (rake and trail).

The solution that you propose to tighten the front axle pinch bolts with the suspension in a particular state will not effect any of the rotating mass, the steering pivot resistance or change the steering angles. I am not saying that what you have experienced does not have some validity, just curious how it could work. Can you explain how your proposal would do what you say it does?

 

[gumba]

I lived with this head shake for the better part to 39 years, off and on. Recently I did the Penske and fork spring thing with fresh rubber and it reappeared. Started to think front end alignment.

Read on this forum where someone suggested that you tighten the front Axel pinch bolts with the fork tubes completely relaxed. That's where its at. This implies that the front end be jacked up. For 39 years I would compress the forks with the brake on and then with weight on the front tighten the pinch bolts. Hell I'd do this with single caliper front brakes. WRONG Now I compress the forks without the brake and then jack-up and go through the tightening sequence. The Gen2 shop manual goes through an elaborate description of how to tighten those pinch bolts.

Got $100 that says I can take that shake out of your front end in 10 minutes - don't care how loose your steering neck bearing are or how out of balance your tire is.

If I sound over excited, Remember it took me 39 years to get here.

Being a thinking man, I can't quite understand how what you say above can be true.

The root cause of head shake (especially at a specific road speed) has to be due to some rotating mass on the front end (wheel, tire, brake rotor). It can be mitigated (dampened out) by friction in the steering pivot, either a more restrictive steering head bearing like tapered rollers or by increasing the bearing preload or by adding dampening like with a steering stabilizer. It can also be lessened by relaxing the steering angles (rake and trail).

The solution that you propose to tighten the front axle pinch bolts with the suspension in a particular state will not effect any of the rotating mass, the steering pivot resistance or change the steering angles. I am not saying that what you have experienced does not have some validity, just curious how it could work. Can you explain how your proposal would do what you say it does?

 

[RadioHowie]

Gumba, I didn't get that....

Would you mind repeating it, please?

(ps: It IS the tire)

 

[ionbeam]

Gumba seems to stutter when we get him excited Either that or he has found that using the Back button while trying to write a reply is a bad idea.

[Public Service]

Go to your first reply and click Edit, type Ctrl A (select all); Ctrl X (delete all). Type Oops! Now type your reply. Move to your next duplicate reply and type Ctrl A (select all); Ctrl X (delete all). Type Oops! Repeat as necessary.

[/Public Service]

 

[gumba]

I lived with this head shake for the better part to 39 years, off and on. Recently I did the Penske and fork spring thing with fresh rubber and it reappeared. Started to think front end alignment.

Read on this forum where someone suggested that you tighten the front Axel pinch bolts with the fork tubes completely relaxed. That's where its at. This implies that the front end be jacked up. For 39 years I would compress the forks with the brake on and then with weight on the front tighten the pinch bolts. Hell I'd do this with single caliper front brakes. WRONG Now I compress the forks without the brake and then jack-up and go through the tightening sequence. The Gen2 shop manual goes through an elaborate description of how to tighten those pinch bolts.

Got $100 that says I can take that shake out of your front end in 10 minutes - don't care how loose your steering neck bearing are or how out of balance your tire is.

If I sound over excited, Remember it took me 39 years to get here.

Being a thinking man, I can't quite understand how what you say above can be true.

The root cause of head shake (especially at a specific road speed) has to be due to some rotating mass on the front end (wheel, tire, brake rotor). It can be mitigated (dampened out) by friction in the steering pivot, either a more restrictive steering head bearing like tapered rollers or by increasing the bearing preload or by adding dampening like with a steering stabilizer. It can also be lessened by relaxing the steering angles (rake and trail).

The solution that you propose to tighten the front axle pinch bolts with the suspension in a particular state will not effect any of the rotating mass, the steering pivot resistance or change the steering angles. I am not saying that what you have experienced does not have some validity, just curious how it could work. Can you explain how your proposal would do what you say it does?

 

[RadioHowie]

Ahem!

 

[SLK50]

It took him 39 years to figure out to install his front wheel. I think we can give

him a few hours to figure out how to post a reply. K?

 

[Woketman]

Oh that is sweet!!!!

 

[Fred W]

Tires do not wear completely evenly because tires are not 100% completely even. They have a tread and along that tread or hib of the tread you'll get a little more wear. The older the tire gets, the more wear. Towards end of life you can feel it with your hand just by rubbing along the tire. We all call that scalloping. Low pressure will cause it to happen sooner. Most recommend running your tire at maximum rated pressure, unless you want it lower for a specific performance reason.

Biggest difference between PR2s and other tires is that PR2s have a symentrical tread pattern. They scallop as well but because the treads are matched on each site, the scalloping will match on each side. So with these ties, you don't tend to get the wabble, but rather later in the tire life, you get a little bit of vibration as the scalloping starts to have some impact.

While it is true that the tread pattern is symmetrical, every other front tire tread pattern to date is symmetrical too, AFAIK. Although it may make some great sense to make them asymmetrical I don't think that any tire manufacturers have gone down that road (yet?). The reason for asymmetrical wear is that we can not ride down the middle of the road. In the right side driving world you will spend more time rounding corners going left due to the larger radius of those corners. With the crown of the road being to the rider's left you'll also apply great lean angles for a given corner radius and speed when taking lefts than rights.

The PR2's do scallop as they wear. You can feel it as a fairly high frequency vibration at certain road speeds. It actually puts some people off them as they believe it (may) negatively effect the tire's grip. I believe the big difference between PR2 fronts and any other tires is the size and shape of the dual compound center section. Very few of the dual compound technology tires carry that feature to the front tire.

As you say, all tire tread will wear into a scalloped pattern to some extent. It is due to lateral forces being applied to the tread blocks. These forces make the blocks want to twist or roll, putting more pressure on the edge opposite the force. For example, inspect your rear tire closely. You'll note that the lower (trailing) edge of each tread block (viewed from the rear) is more worn that the upper, leading edges. This is beaucse the primary lateral forces are applied to that tire from the right hand twisty thing. Same situation applies to the lateral steering (and braking) forces being applied to the front wheel, but in different directions. Running at higher pressure allows the blocks to roll less, so less scalloping.

Note gumba stated alignment. Some motorcycles, especially in the past needed to have a procedure similar to what gumba states performed when reinstalling the front wheel. The procedure would typically request that the mechanic get the wheel installed but leave all the hardware finger tight; compress the front suspension,fully release the forks and tighten the front axle then the pinch bolts (if any). In theory this would align the fork lowers and wheels into a true vertical position and be square & centered with the frame. I have seen front wheels that were obviously not square and true corrected by this procedure.

Oh I definitely get the idea of the front end tightening sequence having an effect on front end wheel and fork alignment. What I do not understand is how that would result in a front wheel oscillation (wobble). In my mind any misalignment would result in a constant pull to one side or the other, no?

OTOH, I guess I could see how, if the forks were out of alignment there would be some increased fork slider stiction, which might cause the front ride height to change and thereby alter the steering geometry a tad, possibly making the steering slightly less stable.

This thread is a good start on the PMS parade. (note change of avatar).

 

[SwollenRaccoon]

Many astute, accurate, thoughtful observations here, any of which may be part of the problem, either on their own, or in any countless number of combinations.

That said, as you all know, it's the tire.

The race doesn't always go to the swift, nor the battle to the strongest, but that's the way to bet.

 

[Woketman]

Well, many good points raised here. I shall order a set of PR2s today and get them mounted and balanced some time in the coming weeks. I shall report back if it cured the wobble.

You guys are a great asset to the nominal FJR owner. Happiest of Happy New Years!!!

 

[maddad]

While it is true that the tread pattern is symmetrical, every other front tire tread pattern to date is symmetrical too, AFAIK. Although it may make some great sense to make them asymmetrical I don't think that any tire manufacturers have gone down that road (yet?). The reason for asymmetrical wear is that we can not ride down the middle of the road. In the right side driving world you will spend more time rounding corners going left due to the larger radius of those corners. With the crown of the road being to the rider's left you'll also apply great lean angles for a given corner radius and speed when taking lefts than rights.

Symetrical as the PR2 front tire is

/ \

/ \

/ \

Not symetrical as many other tires are

/ .

. \

/ .

. \

Being an engineer, should have drawn a picture I guess, rather than try to use English. Yes symetrical may not be the right word, but you get my point why the PR2's don't wobble as much when they scallop and other tires do.

 

[Woketman]

Bought the PR2s from Derbycycles.net today. Something like $235 delivered. Best price I could find with a 50 minute search. I also ordered some Ride-On leak plugger/balanceing stuff via recommendation by Patriot. Was going to try Dynabeads, but changed my small mind.

Local shop wants $47.50 per wheel for mounting and balancing. I said "say what MF???" (the other one wanted $67!!!!!) I shall now attempt my own installation. Sounds like fun!

I shall report back my results.

 

[Woketman]

PS. I meant to add the following: Thanks you FJR folks for the help.... This forum is quite invaluable!

 

[Fred W]

Symetrical as the PR2 front tire is

/ \

/ \

/ \

Not symetrical as many other tires are

/ .

. \

/ .

. \

Being an engineer, should have drawn a picture I guess, rather than try to use English. Yes symetrical may not be the right word, but you get my point why the PR2's don't wobble as much when they scallop and other tires do.

Ah yes! So it is.

Your ascii art is worth several thousand words. :thumbsup:

The PR2 tread pattern may indeed help reduce the oscillation at certain speeds.