BMW R1200R R1150R/T F800 K1200R R1100R/T R1250R RnineT Message Board

I have been tempted by this for a long time and finally did it.

the deets:

#6 O-Rings from Lowe's or Home Depot or the like --couple of bucks--come in a box of 10

Two schools of thought:

one on the top and two on the bottom of the shaft of the mirrors

OR

one on the top and ONE on the bottom of the shaft of the mirrors

Install was straightforward, but you are advised to NOT lose the nut as it is prone to falling and bouncing to neverland.

Also, getting the o rings on the bottom of the shaft takes a little dexterity and thinner fingers. I opted for two on the bottom, one on the top.

When I tightened the nut, the shaft continued to be able to swivel in the seat, unlike when there are no o-rings in place.
I tightened more, but was concerned that if I tightened enough I would negate any "cushioning or vibration absorption" of the o-rings. But, they swiveled so easily that I thought without tightening, they could swivel with wind pressure, and certainly positioning the mirror body would be enough to twist the stalk.
I tightened enough that they swivel only with some effort.

Don't know the torque setting, if someone does, please... But it would not be the same one as sans o-rings, I'd think.

On the road

bumpy streets and some smooth streets, at lower speeds, 20-30mph vibration is (much?) improved. Revving to 4k introduces some vibration as does speeds above 30-35. If a regaled police cruiser were 300-500 feet behind you you would not discern the lights on the top or any distinguishing features. 200 feet you probably would and closer definitely.

overall I think they help "some" and much more at low speeds. Engine vibration is dampened but not eliminated. I think road vibration is untouched. In my experience the mod does NOT remove vibration.
My results may be worsened by having tightened the retaining nuts so tight to keep the stalk from swiveling so easily, and maybe someone else who has gone looser could comment.

John

I used 2 O-rings on top, one at the bottom, tightened to 12 NM of torque. In my case, although the mod didn't completely negate vibration, it still greatly improved clarity up to . . . well, legal highway speeds. I did both mirrors in one go. On hindsight, I should've done variations just to be able to compare; 2 rings on top with one mirror, 1 on top with the other, etc. Maybe I'll try this on a boring day.

I'm not a physicist or an engineer. But I can't help but visualize that the mod you are performing could actually accentuate the vibration at the worst RPM's.

Think of the stalk as a spring whipping back and forth ever-so-slightly.

I never had a problem with the mirrors on my R1150R. As long as the TB sync is right on, it stays blur-free. My Ducati is a whole different matter.

I would think that adding a bit of weight to the ends of the mirrors would do more to dampen vibrations than putting O-rings on the stalk. Shouldn't the mirrors be torqued down such that they only vibrate because the mounts are vibrating because the handlebars are vibrating? I'd guess that one or two wheel weights attached to the mirrors would dampen vibration much more effectively. Perhaps, when I find my spare wheel weights, I'll try it out.

I think it's a resonance problem; the resonant frequency of the mirrors is dependent on the stiffness of the stalk and the moment of inertia of the mirror/stalk system. O-rings reduce the stiffness, weights increase the the inertia. The trick is to make the resonant frequency far from the 'exciting' frequency supplied by the engine's vibration -- which varies with RPM.

AirForceDirt wrote:I would think that adding a bit of weight to the ends of the mirrors would do more to dampen vibrations than putting O-rings on the stalk. Shouldn't the mirrors be torqued down such that they only vibrate because the mounts are vibrating because the handlebars are vibrating? I'd guess that one or two wheel weights attached to the mirrors would dampen vibration much more effectively. Perhaps, when I find my spare wheel weights, I'll try it out.

interesting idea, some mass up there probably would help, I may try that also, if the spirit moves

I didn't say that the vibration was accentuated. It was not, rather it was improved...somewhat. I think much of the vibration now is coming from the road rather than the engine...I think. And my tbs are spot on.
I am pretty certain I tightened things > 12nM. I think at that setting the stalks would swivel pretty easily, in an unwanted way. But I will check that.

John

AirForceDirt had it correct about adding extra weight to the end of the mirrors. You can see the cure when you use just 2 fingers to squeeze the outboard edge of the left mirror (while the other hand is on the gas and guiding the bike).

Adding strategic weight made a dramatic difference in the sharpness of the reflected image. See for yourself:

(click thumbnail, then click displayed pic to enlarge it)

That will increase the moment of inertia around the mounting point and lower the resonant frequency. If the frequency is below the idle speed of the motor, then it'll help.

Similarly, reducing the stiffness of the stalk will do the same. You do have to be careful about the resonant frequency, though; if you reduce it to a simple multiple (half, one-third, etc.) then the problem will remain, though probably at a different RPM.

As an experiment, you can "twang" the mirror on the stalk. Listen to the pitch of the sound. If it vibrates at a pitch that the motor can generate, that's the RPM's that will produce the most "fuzziness."

Wow - this discussion has risen far above my head with resonant frequencies. Now I need a twinmax AND an oscilloscope.

so that's what I am seeing...at low speeds I have decreased the whipping of the stalk and at higher speeds have modified the resonance.

Maybe I ought to just slow down