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Discussion Starter #1
ok, I have an o4 roadster and I have less than 20k miles.
at 120 mph, start to feel it coming on. Fork springs and oil are stock. Tire is new.
Just me tossing out ideas and wondering where you would start to find the cure....progressive springs? different weight oil? just add 1-2" pvc spacer to stock springs? tighten the head bearing set up a smidgen? Is it an inherant problem/ issue with 28* neck angle? Install dampener?

(you finish the sentence please)

To cure headshake I should........
 

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yeah, thats prolly the wisest path to the cure:rofl:

I agree...besides..dont the sporty spedometers only go to 120?? Let me go look at mine...Yep she only goes to 120...maybe thats an indication your bike is about to flatline?!?!?:D
 

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I agree...besides..dont the sporty spedometers only go to 120?? Let me go look at mine...Yep she only goes to 120...maybe thats an indication your bike is about to flatline?!?!?:D
Oh, Cupcake.. you are the wise one! :ride
 

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On a serious note, describe the shake you are experiencing. Does it start at a particular RPM? Is it repeatable and predictable? Does it get worse as you go faster? A high speed wobble can occur under heavy accelleration and it can get worse with relatively harsh accelleration/decelleration. It has something to do with weight shifting from front to back under accelleration and back to front on decelleration.


A couple thoughts off the top of my head are to check the fork legs and make sure they are even in the triple trees. Check the wheel balance. Check the OIL level in the forks.
 

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Discussion Starter #7
On a serious note, describe the shake you are experiencing. Does it start at a particular RPM? Is it repeatable and predictable? Does it get worse as you go faster? A high speed wobble can occur under heavy accelleration and it can get worse with relatively harsh accelleration/decelleration. It has something to do with weight shifting from front to back under accelleration and back to front on decelleration.


A couple thoughts off the top of my head are to check the fork legs and make sure they are even in the triple trees. Check the wheel balance. Check the OIL level in the forks.
The shake is very predictable, I can cruise at 120 mph and have plenty of throttle left, so this isnt a weight shift issue I dont think, twist and take it to 123-125 and the shake gets steadily worse. I can back down and it smooths out.
 

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The shake is very predictable, I can cruise at 120 mph and have plenty of throttle left, so this isnt a weight shift issue I dont think, twist and take it to 123-125 and the shake gets steadily worse. I can back down and it smooths out.

Is it really not because you are about to take the bike very far above the speed its meant to go?? I'm ignorant on this, so you'll have to speak to me like you speak to a small child, but I would think that the fact that you are taking a bike that stops at 120 on the Spedo..above that limit, would justify that its getting to its limit..and might shake...I know this isnt that case, but it would make sense to me.

And by me posting this, you can tell I've never taken my bike up that high :)
 

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The shake is very predictable, I can cruise at 120 mph and have plenty of throttle left, so this isnt a weight shift issue I dont think, twist and take it to 123-125 and the shake gets steadily worse. I can back down and it smooths out.
What you are describing is a speed related wobble. Do you run a windshield? It can cause the wobble effect. That's why high speed bikes use a fairing mounted to the frame and not the fork.

An out of balance wheel can do it too. Make sure you balance it with the rotor still attached and with the valvestem cap on. At those speeds, it all matters. Make sure your tire pressure is up to snuff too. At that speed, you don't want to take any chances.

abryson said:
Is it really not because you are about to take the bike very far above the speed its meant to go?? I'm ignorant on this, so you'll have to speak to me like you speak to a small child, but I would think that the fact that you are taking a bike that stops at 120 on the Spedo..above that limit, would justify that its getting to its limit..and might shake...I know this isnt that case, but it would make sense to me.

And by me posting this, you can tell I've never taken my bike up that high
Cupcake, I don't condone speeding, and I rarely do it. But if we limited our aspirations to a number on a guage, no one would ever achive anything.........
 

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Cupcake, I don't condone speeding, and I rarely do it. But if we limited our aspirations to a number on a guage, no one would ever achive anything.........
That's very true....:ride
 

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Discussion Starter #11
Is it really not because you are about to take the bike very far above the speed its meant to go?? I'm ignorant on this, so you'll have to speak to me like you speak to a small child, but I would think that the fact that you are taking a bike that stops at 120 on the Spedo..above that limit, would justify that its getting to its limit..and might shake...I know this isnt that case, but it would make sense to me.

And by me posting this, you can tell I've never taken my bike up that high :)
real world, that may be a pretty true statement, but then again, if we are not standing on the edge, then were taking up to much room:D
 

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Discussion Starter #12
What you are describing is a speed related wobble. Do you run a windshield? It can cause the wobble effect. That's why high speed bikes use a fairing mounted to the frame and not the fork.

An out of balance wheel can do it too. Make sure you balance it with the rotor still attached and with the valvestem cap on. At those speeds, it all matters. Make sure your tire pressure is up to snuff too. At that speed, you don't want to take any chances.



Cupcake, I don't condone speeding, and I rarely do it. But if we limited our aspirations to a number on a guage, no one would ever achive anything.........
yeppers on the windsheild, I know its not the most aerodynamic critter made, its like pushing a half sheet of plywood through the air.
I also installed a fork brace. When the sheild is removed it still gets the shake so I cant blame it all on that.
Sometimes at 90mph I can feel the front end acting weird. I think I will do a new tire again, this time try a different brand. I will also change to progressive springs and different weight oil. I've gotta do something, not because I speed everywhere, but because I know it can't be right and there is something I am missing.
If a bike is set up properly, it should speed on up to where the motor is the limit, not the bike and its stability issue.
I know it can be done, I'm gonna figure it out and go get me a speed record on a sporty. www.TexasMile.com
 

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I'll bet some of the time, "speed wobble" is induced by the rider holding on too tight, and causing a feedback. That seems more likely than suspecting there is some design characteristic like the rake, everybody would be talking about a standard characteristic. Next time it tries to wobble, let go. :D
Or at least lighten up, and if you're holding so tight you can't lighten up, that's even more likely to be the cause.

As if I know ANYTHING about riding that fast.
(Amy, you aren't the only one..)
I'm a pretty sedate rider, DEEPLY convinced that old saying about pilots
is perfectly at home describing motorsickle riders.

"There's OLD RIDERS and there's BOLD RIDERS ,
but there aren't very many OLD BOLD RIDERS."
 

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One more thing to consider, are your tires up to operating at that speed? A tire outside its speed range may begin to expand in an unstable manner due to centrifugal forces, and would be most prononced at the center of the tread, lessening as it proceeds down the side of the tire. and you might if you really like to go that fast very often, do the balance proceedure as periously outlined,and then have the tire trued. its done by spinning the entire wheel and having an absrasive wheel trim off the out of round parts of the tread. I dont know if this is needed in this day, and age, but it was needed in the 60's if you wanted a balanced and true running highspeed wheel. The fork oil might need changing as well, the stock juice might be foaming at those speeds, so see if there is an oil suitable for high speed use. just thoughts from my aged brain, T-Head.
 

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I'd be curious if there is any shake at any other speed, no matter how slight.

Look at the weights on the new tire. Many times, if there is too much weight on one side, the tech will turn the tire on the rim and re-balance.

Sometimes it is just this simple.

Was there a noticible shake anywhere before the tire change?
 

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There are a couple other things we used to do in the good ole days, with hydro forks, (you had a choice in those days, ) sometimes if the dampening wasnt right, we would drill out the holes in the metering disks, and change the springs to produce whatever differences we needed. sometimes we would change oil viscosity as well, so it would dampen more smoothly.you might be able to get fork parts that will be responsive enough to articulate properly at the speeds you run at. and while you are at it,, if your bike is older than 2-3 yrs,, try checking the swingarm bearings/bushings whatever they use nowadays. a little slop in those, and you can wobble as well.
 

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From my dirt bike racing days I learned that often if you have handling oddities in the front end, you look to the rear end and vice versa. Make sure your rear tire is inflated and balanced and most importantly properly centered and aligned. Make sure you have the same springs and settings on your shock. Swingarm bearings, etc. You might be surprised.
 

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Discussion Starter #20
update for those who care.
end result, I swapped to new tires front and back and it solved a whole bunch of it. I can zip to 120+ in 4th gear in a blink, then hit 5th and tap it on 130 with zero wobbles.
Avon Venom X tires are teh bomb
 
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