Front wheel shimmy

Tires.

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

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

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

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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.

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

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

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.

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

Click to expand...

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.

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

As soon I as read you had Bridgestone BT020, I knew what caused the front shake.

Every bike I have owned with Bridgestone, once they start to wear on the front, have develop shakes around the 70-80 kilometers.

Once the tyre starts to wear, uneven scallops and bumps appear on the tread pattern.

Barry

Thanks to all for the replies.

It looks like majority are leaning towards tires. Interesting that I am not alone in having had the same thing happen to relatively new tires as well. As it is not really an issue and only occurs with hands off the wheel, I may just go for the distance record on the BT's. and try lower reloads and slightly lower pressures to see if it changes.

What is the record on BT020's anyways? With 1.5mm left to the wear indicator, I should make 10,000k. :wink:

CM