What is the cause of hands off,headshake

hobot said:

[video]https://www.youtube.com/watch?v=xzB6KSlD6ec[/video]

Click to expand...

Fun/scary video to watch, but I would submit almost all of those were caused by too much power out of the turns, or going across an anomaly in the track's surface. One at 2:21 looks like a legitimate wobble, but it's such a short shot that it's hard to tell what might have led up to it.

Back to the 30 mph wobble. I had a metric bike in the early 80's that I had added a factory-offered handlebar-mounted fairing. In the kit was this insane flat plate of cast iron (no foolin') that weighted around 10 pounds/5 kilos that was supposed to mount inside the fairing below the headlight, laying flat and projecting forward, away from the steering stem. "Piss on that" I thought, as I didn't want the added mass added to the front end. Well, I quickly changed my mind. What started out as a very nice handling, well-mannered bike turned into a head-shaking piece of crap that did everything it could to toss me off coming out of anything resembling a high-speed sweeper. And, it shook its head in a rapidly increasing manner at the dreaded 30 mph. None of this was present before installing the fairing. Most likely wind turbulence around the fairing contributed, but I couldn't believe just how bad it was.
Bending to pressure from this nagging voice in my head, I attached the dreaded weight. Problem solved! Apparently, it moved the oscillation point of the front end into a frequency that no longer jived with whatever it was in the frame that was causing the issue.
Point being, there's so many things in the system that could interact with each other in ways unseen/not understood that it could take many hours of experimenting to able to decipher out to their root cause. As for the mild head shake with the hands off the bars, like the cheesy skit from Hee-Haw goes, "Doctor, it hurts when I do this" "Well, DON'T DO THAT!"

That being said, try changing tire pressures. shifting your weight, and adjusting the rear shock's preload to vary the rake/trail of the front end to see what, if anything, affects this wobble. You may find that the mild head shake is the least of the bad handling characteristics.

Nathan

Once I got rid of the rim offset, my Commando lost the tendency to pull left. With the puck-type head steady, head wobble is minimal. I can sit up and adjust my gloves without a tank-slapper. I can coast hands-off long enough to determine how to fine-tune my wheel alignment without significant wobble.

Manxman[/quote]

This evening, I took the Commando out for a head-shake trial. I took the bike up to 70mph, then took my hands off the bars and let it coast down to 20mph. No head shake. I repeated it several times. The pavement had a normal selection of bumps, gravel and pot hole covers. Other than a puck-type head-steady, a link butt-steady and a properly laced front wheel, it is a stock chassis. Tires are newish TT100's, balanced and properly inflated, but there is no steering damper.

If this bike doesn't shake, I don't see why any Commando should shake if it is set up similarly.

Manxman

I agree, however I think its a indication that something is wrong. No modern bikes do it.

Click to expand...

yes, they do. You should see the anguish on the FJR1300 forum about this deceleration headshake with both hands off the bars.Or the Buell forum. Or probably any forum, should you wish to dig. The castoring effect was described earlier in this thread. Laughable really, some people are so anal. Happens when front tyre is a bit worn, FJR1300's are the only bike I have ever seen that wears their front out before their rear. Mine did it when the tyre was worn, my Mk111 does it when the front tyre is a bit worn. Answer, as others have pointed out, keep one hand on the bars.

also the pan weave
https://www.google.ca/search?q=PAN+WEAV ... fUesvzgpAJ

http://www.motorcyclenews.com/news/2007 ... scoroner-/

The castering effect of auto onset of straight steer back to counter steer is on canging scale of tire- surfaces and loading conditions > Wes and me encounter this out The Freaking Blue just timidly crossing THE Gravel in 25-45 mph zone and d/t nil traction to counter-recover - we have both crashed half dozen time each w/o knowing whatthefuck when wrong. Wes and I pretty much Have to Keep Both hands/arms on bars with mostly wasted effort, just in case the front suddenly goes nuts all way down. It only takes one 1/2 tank slap on THE Gravel for a hamburger patty. Powering front out of being the main traction patch does help on and off road ala the motto - when in doubt POWER IT OUT- but can just as well slam down faster-worser. In the non injury crashing video one fella wheelies right after upset apex to settle bike down. Its funny to me on the level of skill and experience shown in the elite racer video, seasoned pilots just shug it off and carry on while the uneducated ones all look back to see if they hit something or want to see the skid marks, LOL. An extra round stone or two in a hole or small animal runing under wheels can induce this too and have seen rabbit run right between Wes 71 tires in a turn with him looking backdown in shock he missed it somehow.
Cycle hobby is risky business

[video]https://www.youtube.com/watch?v=6cmK8dCX5ug[/video]

I could ride my 1st Commando (72 interstate ), back in the 70s, at any speed, hands free. No wobbles or left lean.

My Mkiii developed a severe 30 mph hands free wobble. Had old, but with good tread Dunlop on front which I replaced with an Avon. Improved greatly but not cured. Found slight play in swing arm. New bushings and wobble is gone. No left lean.

The factory front rim on my 74 850 was offset almost 1/8" too much toward one side. I had it relaced by Buchanan's for stainless spokes and the left lean went away. I had lived with that for over 30 years, from the day I rode it off the dealer's lot.

Front tyres tend to dry out before wearing out on a Commando. A few years ago a buddy noticed that my Avon AM20 had some scalloping. I replaced the tyre and balanced the wheel and my headshake went away.

BTW the Norton dealer told me that left lean was "normal" on a Commando.