Shimmy developed

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Eband

Member
Como 2.0 @ 6K miles:
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OK obviously you're supposed to keep hands on bars even on well paved roads I ride on :

.. but now if raise hands off bars at all, scary shimmy starts, goes into destructive oscillation unless bars grabbed quickly ! .
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Until very recent development could cruise without hands on bars effortlessly never a shimmy ! - ?.
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Wheel/tire spin as true as I can see by eye, headset is tight, - what may contributes to problem ?.
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thanks
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Are you carrying ANY weight on the rear tire,
with a rack or basket?
Find out the recommended torque tightness is from the suppliers and check the torque settings.
My bike was not even close.
 
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front tire looks fine with tread intact and no odd wear pattern. Headset seems tight with no play. Pick up wheel and spins with no wobble or eccentric deviation. Light dampening with finger on bars prevents oscillation.
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last comment mentioned REAR tire load, and I did just mount a child carrier on it recently. Child carrier matched same mount as our other matching COMO which has had the carrier and kids for @ 3 years with no shimmy . ( Haven't noticed shimmy with kid on it but probly kept hands on bars. Carrier is only a few pounds, easily carries 30 lb kid ) . Carrier is easily removed leaving the small light rack , I will try removing carrier and ride ...
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identical but no shimmy one of our two Como's with kid carrier.


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thanks for responses .
 
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THANK YOU -

Nvreloader​

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removed the child carrier from the carriers' rack receiver and does not shimmy !. - 'my' Como of our identical pair, the child carrier identically setup, appears to produce an uncontrollable shimmy of front wheel/bars if hands are not kept tight to bars.
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seems hard to believe, carrier weighs @ 5 pounds (US) ! - going to mount carrier back to rack and test ride to confirm this odd assumption/finding ...
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IMG_6925.JPGIMG_6926.JPG
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have fun

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Eband
Glad I could help. I will be looking for your results.
On my bike the racks/baskets are rated for 35#'s for F/R.
I found, out I can't carry that amount and be free from the HB shimmy.
I believe that the CG = center of gravity/balance point is right on the 90* line of the rear tire axle, and any amount of weight on or behind the axle causes the HB shimmy, imho.
So I am attempting to find a work around, as I am not riding without the required safety gear, where I ride. ymmv
 
TOTALLY UNEXPECTED - our Como that has had same carrier ,'the other one', DOES develop a shimmy with rear child carrier, just takes longer to start...
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Harmonic Resonance? - CG offset?, hard to believe such little weight difference can cause / effect ...
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is front fork rake a factor?, seems very light.
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the child carrier is well engineered for 'universal use' and offers considerable protection for kid
 
Weight on the rear was my 1st though as well. If you can move some of that weight in front of the rear axle, it might help.
 
Eband said:
TOTALLY UNEXPECTED - our Como that has had same carrier ,'the other one', DOES develop a shimmy with rear child carrier, just takes longer to start...
.
Harmonic Resonance? - CG offset?, hard to believe such little weight difference can cause / effect ...
.
is front fork rake a factor?, seems very light.
.
the child carrier is well engineered for 'universal use' and offers considerable protection for kid
Click to expand...
I would be willing to bet, that with the kid in/on the back, your could have a real case of HB shimmying, so please be careful.
You can do some tests to find out, a gallon of water weighs in at about 8#'s, add enough gallons to the back to get the kids weight and test. Better to know than find out the hard way.

What are the OEM limits for weight on the bike?
What does the carrier weigh?

"is front fork rake a factor?, seems very light."
I don't know, as I am attempting wrap my head around the fork rake angles etc.
Lots of reading to do and I am NOT engineering type person,
so I am in over my head as usual lol.

I did some testing, on my bike the max weight/carrying capacity was 330# - 200#'s my weight = 130# = remaining capacity.
The OEM info states 30#'s per basket.

Started test with 125# = 25#'s per sack, with the 5 sacks on the
back in the basket, spread out, I rode for 20' and thought I was going to be thrown off because the shimmying was so bad.

I kept moving 1 sack of weight at a time, to the front, until I had 100#'s on the front basket, shimmying reduced to Zero.

Rode home and dropped all the sacks off except 1,
which I kept in the front basket, I could ride with no hands on the HB, (not very good at this), with the 1 sack.

If I added another sack of weight to the rear basket, the shimmying started to increase, with every weight added..

I have 2 packs of survival gear/bike tools etc, that I carry ALL the time, I ride cross country and I am at a minimum of 5-10 miles from the nearest road with very spotty c service, 1 pack weighs in at 30#'s, the other at 25#'s, 10#'s for the water/camel bac, and 5#'s for the bike locks/cables/security etc.

I am in the process of carrying the big pack on the back, up close as possible to the seat and the rest of the stuff in the front basket.

There is a slight HB shimmying, when I hit wash board type conditions, very common around here, but I can control it without too much problems, so far.
I haven't tried any speed yet, I normally ride in the 10-12 mph bracket, when I am not crawling along on the cow/horse trails.
Still testing, ymmv
Tia,
 
Rake matters, but that's something that's difficult to change. There are headsets that can alter head tube angles a little bit, or you could use a different fork. Would it do anything to change the resonance? Who knows? A steering damper would help, but I don't know anyone who makes those for bicycles. And it doesn't change the fact that you have too much weight too far back - which will affect cornering.
 
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