Front wheel shimmy

[cm08]

Hi guys,

My ST has a front wheel shimmy, but only above approx. 70km's and when I sit up with my hands off the handlebars (like when rolling into a light at an intersection. Otherwise runs and feels very stable. I am pretty sure it was not doing this a couple of months ago. Items that may be related.

1. just changed fork oil and removed forks. Oil level in the forks was originally low on both forks and I topped it up as per the manual. Forks are much stiffer now.
2. just cleaned pins on front brake and since then started hearing a clicking noise (maybe was there before and didn't notice)
3. front tire has 7500km's on it.

Is this normal? I know it used to happen on my Honda as well and that was after installing a new tire.

CM

[DaveM]

cm08,
have you checked your tyres pressures?
What are you running front and rear?

If your pressure is high and you have now firmed up your forks this could explain why you exhibit this problem.

Also your front tyre may have worn in a manner to cause this.

What tyres are you running and what milage do you normally acheive.

For exaple I have personally never acheived as much as 7,500kms on any brand or type of rear tyre on any bike I have owned so for me that would be a very excessively worn tyre.

DaveM

[triumphite]

Tires.

It was doing it on mine. I just put new ones on. It stopped.

[cm08]

Dave M, I did pick up from many other threads that your strong point is not tire longevity. I am running with bridgestone BT020F tires. Tire pressures 2.5 kPa front , 2.9 kPa rear. Tread depth at farthest points from center are 3.2mm (at the chicken strip zone), 2.6mm at center. There is 1.5 mm remaining to the witness - max wear marks.

Just backed off 1/2 turn on the preload, went for a 100 km run today and the shimmy is much less. Again this is only when I take my hands of the bars and sit straight, removing all weight off the nose. With one hand on the throttle or leaning slightly forward everything is quite stable.

Triumphite, I would also normally assume tires, except for the above supporting DaveM's comments about the front suspension and tire pressure potentially causing this. Also as I said in the original post, I have had this happen on another bike with brand new tires, left it like that and had no ill effects.

CM

[Yimm]

1. just changed fork oil and removed forks. Oil level in the forks was originally low on both forks and I topped it up as per the manual. Forks are much stiffer now.

CM

CM:
Unless your fork oil was very low, say more than 30mm, or you changed oil weight, your forks should feel the same after the oil change as before. Raising oil level will effect the feel only at the very end of travel. just before bottoming.

It is also recommended that you align the forks before the final tightening. After you tighten the axle, pump the front end hard with the brakes held on a dozen or so times. Then tighten the axle clamp screws.

And did you check the steering head bearings while you had the wheel off?

Having said all this, as Dave said, it is much more likely to be the tires, but it doesn't hurt to dot the Is and cross the Ts. Hope this helps.

[cm08]

Hi Yim.

thanks for the info

Both forks measured identical numbers when I measured before the drain and flush. 189mm down from top of forks instead of req'd 145mm and 390 ml drained oil instead of required 459 ml. This is why they now feel much stiffer.

In regards to aligning the forks, I am not quite sure what you mean. Are you suggesting to tighten all the screws including the 4 top pinch bolts securing the forks, except for the 2 screws on the left fork at the axle?

CM

[oldgoat57]

i know this is a long shot but, have you done a chain adjustment lately ? The rear tire might not be running straight ?

[trotsky]

I would go with cupping on the tire...happened on a honda I had and the bandit I sold last year too.

Changed out the tire and it was as good as new.

[Yimm]

On 2007-01-14 13:09, cm08 wrote:
Hi Yim.

thanks for the info

Both forks measured identical numbers when I measured before the drain and flush. 189mm down from top of forks instead of req'd 145mm and 390 ml drained oil instead of required 459 ml. This is why they now feel much stiffer.

In regards to aligning the forks, I am not quite sure what you mean. Are you suggesting to tighten all the screws including the 4 top pinch bolts securing the forks, except for the 2 screws on the left fork at the axle?

CM

All the damping happens in the cartridge tube in the bottom 10" or so of the fork. My experience has been that if the oil gets low enough that the dampers are actually sucking air, the forks will stutter as they pass the air and you'll know immediately. Anyway, who knows.

As far as aligning the forks go, my experience is mostly on Japanese bikes that have axle pinch bolts on both sides. I always torqued the steeering head clamps and axle to spec, pumped the forks, and tightened the axle pinch bolts one side at a time, pumping again between tightening one side and the other.

I have also known mechanics who torque the triple tree clamps to spec on one side, and on the other torque the top tight, but set the bottom loose to, say, 5 ft.lbs. Torque the axle to spec. Do the pumping routine. then torque the second triple tree clamp, and finally the axle pinch bolts. Hope this is more clear.

[dolson]

I would look at the front being cupped. I've had this happen after less than 500 miles on a new tire. I started feeling a slight shimmy after 200 miles.

Don