KymcoForum.com
General => General Discussion => Topic started by: 08087 on December 14, 2012, 08:40:20 PM
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Ok I'm becoming a better rider, more confidance in my ability, and we all know what that means...yes, taking more chances and risks.
So knowing in my car if I loosten my grip on the steering wheel and the car pulls to one side I have a problemwith aliengment or a brake holding. So the other day I go to my favorite training grond with the scoot (NY Giants stadium) so I turn in and at 20 MPH release the handle bars and see what happens. good for e nothing happens and I sow down.
SO today I go back and ride around doing sways, figure 8's, circles etc. At 40 MPH I relesea my grip and the front end shimmy's after a couple of seconds uncontrolably. I slow down to 20 MPH and try again, the bike id steady as a rock, back up to 40 MPH and a bad shimmy again.
When holding the bars you can't feel it what so ever, I've not hit anything too hard that I can think of so I don't know what would cause this. I don't see any damage to the tires or wheel rim, air preasure is good and I don't feel any play in the steering mech. at all, any ideas what it could be and what to look for?
Thanks in advance!
08
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have you put a plug in your tire, that could put it out of balance just enough to make it shimmy or you hit a pothole and lost a balance Wt. ???
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Many bikes and scooters have a shimmy at some speed. They usually develop one with a
top box so people put heavy bar end weights to mellow it out. It comes from a resonance
in the system. Loose head bearings, a long travel soft fork or even worn rear shock can
make for a big shimmy. I wouldn't really worry about it unless it starts doing it while your
hands are on the bar.
I had a big single cylinder road bike and was up to Lake George. I took it for a ride on a
long straight road next to the highway and decided to crank it up to see how fast it would
go. Well at around 90 the whole bike started shaking, the footpegs felt like rubber moving
at least 2" up and down. I backed it down and when I got home I tried tightening the motor
mount bolts (they didn't seem loose) but I never had it happen again on that bike....
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I would say I experience this shimmy at some point on most of my bikes/scoots I've owned...when releasing my grip on the bars. Not a big problem unless your vehicle goes into this kind of dance at speed (50+) with your hands solidly on the bars. Then it's LOOK OUT time! And you get thrown....
Holding onto the bars acts as kind of a 'damper' that quells the shimmy. On both of my scoots, it's due to the top cases over the rear axle. Both my Super 9 and Yager track remarkably straight and true even if I remove both hands off the bars (not recommended) But attach the top case and at some point (speed) the bars will exibit bad behavior and want to ocsillate. It's not the scoots fault, they were not designed to be a Gold Wing!
My Honda Nighthawk exibited this behavior with a fairly large windshield, saddlebags, and a trunk. I had the dealer check everything, and even had an independant mechanic try to experiment with bags off, no windshield, or any combination to see what was causing the problem. After checking EVERYTHING including front wheel bearings and tire pressure, he ended up making a custom bracket and mounting a BIG ASS steering damper that took care of the problem. Mostly.
So, I guess my point is, after you check the tire pressure and front steering bearings, and the wheels / brake discs look to be true, and it's just a mild shimmy there may not be much you can do about it.
Wil B.
Broadview, IL
'71 Guzzi Ambassador
'91 Nightrhawk
'04 Kymco Super 9
'10 Kymco Yager 200gt
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...my super nine will track straight, even at 45+ mph with hands off...
..my a50 would pull hard to left without hands...
..like moto said, don't sweat it so much unless you do feel it with hands on...
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I would say I experience this shimmy at some point on most of my bikes/scoots I've owned...when releasing my grip on the bars
..i put 2" long, 3/4" SAE hex head bolts in the ends of the handlebars, in place of the oem caps on my guilty..
..helped tremendously with front end stability, as I'm over 6 ft tall, and ride with my ass closer to the rear tire than a lot of people...
..sorta in a sport bike posture...yeah, i'm a sight!!...
..not an issue on nina tho...
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en.wikipedia.org/wiki/Speed_wobble
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...years ago, think i was 17, hadda old honda 550 four...
..went WOT down a lonng downhill run onna back country road...got halfway up the other side, and the front went into a high-speed wobble...
..nearly soiled my drawers before i got it stopped...
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Ok I'm becoming a better rider, more confidance in my ability, and we all know what that means...yes, taking more chances and risks.
So knowing in my car if I loosten my grip on the steering wheel and the car pulls to one side I have a problemwith aliengment or a brake holding. So the other day I go to my favorite training grond with the scoot (NY Giants stadium) so I turn in and at 20 MPH release the handle bars and see what happens. good for e nothing happens and I sow down.
SO today I go back and ride around doing sways, figure 8's, circles etc. At 40 MPH I relesea my grip and the front end shimmy's after a couple of seconds uncontrolably. I slow down to 20 MPH and try again, the bike id steady as a rock, back up to 40 MPH and a bad shimmy again.
When holding the bars you can't feel it what so ever, I've not hit anything too hard that I can think of so I don't know what would cause this. I don't see any damage to the tires or wheel rim, air preasure is good and I don't feel any play in the steering mech. at all, any ideas what it could be and what to look for?
Thanks in advance!
08
There is nothing wrong with you scoot. What is wrong is that you should not remove your hands off the handlebars while driving. Period, problem solved.
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Most people tighten the steering bearings or add a steering dampener.
I thought my scoot needs more weight over the front wheel so plan on adding
some lead weight right under the steering stem. There are already untapped spots
that are used to attach a high front fender on some models;
(http://i1061.photobucket.com/albums/t478/MotoRandy123/Holder/DSCN2250.jpg)
It should add some weight to the system so change the resonance frequency. You can get 5 lb
lead disks here;
http://www.rotometals.com/product-p/leadcastdisc.htm (http://www.rotometals.com/product-p/leadcastdisc.htm)
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It may also have to do with de-cellaration & the centrifical clutch taking more of a load off of the front wheel as the clutch drags down the engine? :-*
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..scoots are designed (weighted) to have handlebars held at speed...lol..
..i ride with more of my bodyweight toward the center/front on my scoots...
..scoot handles better that way...
..if i ride sitting back, with feet on the floorboard, my front gets very light on takeoff...
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Get you one of these. http://www.amazon.com/gp/product/B007ST5U06/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B007ST5U06&linkCode=as2&tag=kinderinfocom-20 (http://www.amazon.com/gp/product/B007ST5U06/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B007ST5U06&linkCode=as2&tag=kinderinfocom-20)
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Thanks to all for your input, thanks for the photos also and persoanl exp. Axy you seem to miss the point, I know it's not smart to take ones hands off the bars as I worded my OP ( please re read) I also explained why I let my hands lose of the bars, seems like I'm not alone in doing also.
I'm wondering if my full winsheild has anything to do with the shimmy (Juice, I could not open the link but will try to google it thanks) as wind may hit it in an uneven way. I don't suspect this as the cause but it may contribute. I'll try with my body weight towards the front more but don't think that will matter either, my best guess is it's the fork or... want to add more but am getting called away, check back soon.
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I would imagine the windshield has a lot to do with it myself.
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Ya a big windshield could do it. Ever tried holding on to one end of a board and pushing
it through the water? It shimmy's back and forth trying to throw the water to this side
or that. The air acts like water against that big board of a windshield...
Almost anything you do can change it air pressure in the tires, fork oil, rear shock preload,
weight on the bars, tilting the windshield more, etc... So try a few things and see if it helps!
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Thanks to all, I was just worried that even though the front fork feels solid I might lose it while driving down the road one night at 50 MPH, not as pleasent thought.
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+1 on the sheild...
...previoudly unmentioned factor...
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Mine started doing that at one point. And, I'm not like some people. Nothing wrong with doing that as long as you're doing it in a safe area and you're ready to grab the bars in an emergency. I think it is good to do every once in a while to feel how the bike is traking. Anyway, I figured out it was caused because the front wheel nut was loose. I don't understand either because it's supposed to be a locking nut but I could turn it with my fingers :o. Come on Kymco! Anyway tightened it a little and problem immediately went away. Don't want to tighten it too much or your front wheel won't spin free. Another thing it could be is your front tire. My dad has a big Yamaha cruiser (1400cc) and it was doing it too. He put a new front tire on and it stopped. I have heard it could be a loose steering column bearing too. Another thing is sport bikes can get this without removing hands from the bars and they call it "head shake". It's caused when the power of the bike makes the front end very light to the point where it's barely touching the ground. It's a big issue in motorcycle racing and has caused many crashes. Do a youtube search for "head shake". Anyway, I don't think this is an issue with scooters :D. Zombie's ZX maybe :D :D. The point is a number of things can cause it.