Handling question.

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cross
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Re: Handling question.

Post by cross »

At what speed to you get shimmy?
I have Bridgestone spitfire and I noticed that if I let go of handlebars at about 55, while slowing down it will start to get head shake around 50 but as soon it passes somewhere between 49 and 45 it stops.
I found this out as I let go Hadley bars to zip up my jacket and I don't know if it was doing this before.
My tires are ready to be changed but I did notice that front tire, on the sides isn't straight. When I move my hand over the sides I can feel unevenness.
I was going to get Michelin pilot active but still thinking about it
Sasha

'82 Honda CBX
'99 Triumph TBS
'01 Honda Valkyrie

:auto-sportbike:

rsuarez
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Re: Handling question.

Post by rsuarez »

Main reason for handle bar shaking is frame geometry. To steep steering angle will reduce rake and will affect bike stability. If for any reason your bike is too high on the back it will affect you. Think if you have a taller rear tyre or if your shocks are higher than normal, other place to look is your front springs for fatigue. It is true that weight distribution is important, but geometry is more. This is the reason of why modern bikes like BMW or Ducats have electronic leveling devices to set SAG according to bike's load. When a bike is in the border line of being un stable, then tyre wear, balance, alignment and basically any detail makes them very sensible. The benefit of these aggressive an nervous geometries is a sharp and agile turning bike.

Think of this, its know, and already said here, that when experiencing shimmies you should never brake or let go throttle aggressively, if it was a weight distribution problem the front loading of braking would fix it... but in fact it makes it worst. Thats because when you brake the bike dives the front and the steering angle gets more radical increasing the problem.

Sorry if I am explaining something to basic but since no one was mentioning it I just jumped in.

Best.
Rsuarez
1971 Triumph Daytona, 1979 Honda CBX, 1979 Ducati 900GTS, 1984 Honda 200XR, 1992 Gilera CX, 2009 KTM 990 Adventure, 2016 KTM 250 2t Six Days, 2018 BMW K1600B

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cross
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Re: Handling question.

Post by cross »

Everything that you explained does make perfect sense and there are bunch of write ups on here about it.
Front springs are most likely tired after all these years. I also did install progressive brand mono shock in the back but i made a mistake of not measuring height of the bike before removing OEM shock so that i have something to compare it to. Another thing that i don't know is if bike had the same behavior before shock upgrade as i said, i found out about this by accident when i let hands off handle bars to zip up my jacket.
Otherwise bike handles fine.
I'm planning on upgrading forks with racetech springs and gold valve emulators soon anyway and i'll report back.
Thanks
Sasha
Sasha

'82 Honda CBX
'99 Triumph TBS
'01 Honda Valkyrie

:auto-sportbike:

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wyly
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Re: Handling question.

Post by wyly »

I've made several changes to the Z and haven't had a repeat of the shakes, even when trying to replicate the conditions, which was a compression in a high speed sweeper.

I moved my riding position forward tight to the tank.
Replaced the oem plastic swing arm bushing with brass.
Replaced the rear shock with a better unit that lowered the rear by 1/2"
A larger front tire.
added a small windscreen which will add some down force.

whether any one of those things corrected it or a combination or all combined (maybe none) I can't say but it hasn't returned. :handgestures-fingerscrossed: I've become confident enough to remove both hands from the bar to do jacket zipping, which is probably foolish since I don't know if it's resolved.

I'll change to a sports kit as soon as I can, I'm a bit scrunched up now and the sports kit would allow me to stretch out and lower my center of gravity.

maybe a fork brace in the future and or race tech fork modification.
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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FalldownPhil
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Re: Handling question.

Post by FalldownPhil »

It used to be said that placing a watermelon on the tank would cure the shimmy.
They have done it since day one at that 55-60 mph. Just let go of the bars and there it is.
A watermelon (or forward weight placement) on your tank will fix it :-)
This is a well known cbx cure all.
Best,
Phil
When you are up to your ass in alligators it is sometimes difficult
to remember that your objective was to drain the swamp !!

letxbruce
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Re: Handling question.

Post by letxbruce »

While stripping my '79 down with the fork tubes and handle bars removed found the triple tree was incredibly notchy while turning left and right from straight ahead. I suspect that 45,000 miles hammered flat spots in the stearing head bearings. This notchiness could not be felt with the weight of the tubes and wheel attached. New bearings and races along with installing needle bearings in the swing arm made a world of difference in stability. Of course, at best it's still marginal compared to new bikes.

Bruce

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Re: Handling question.

Post by daves79x »

All CBXS need the steering bearings replaced by 20,000 miles. Do Bruce's test and see.

Dave

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Re: Handling question.

Post by rpleines »

As referenced a few times ealier in this thread " The watermellon solution"

http://www.cbxclub.com/Xpress/200301_38.pdf :face:
Rich Pleines

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FalldownPhil
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Re: Handling question.

Post by FalldownPhil »

Thank You Rich,
That's what I was referring too !!
Hope that you're well.
Best,
Phil
When you are up to your ass in alligators it is sometimes difficult
to remember that your objective was to drain the swamp !!

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Sharpie66
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Re: Handling question.

Post by Sharpie66 »

daves79x wrote:All CBXS need the steering bearings replaced by 20,000 miles. Do Bruce's test and see.

Dave
I couldn't agree with this more. When I acquired my '82 CBX 4 years , she had a very pronounced wobble around the 45-55mph range. Rather scary actually. A new set of tires didn't take care of it so I researched this forum on what to do. Dave's advice was to change the steering bearings. With the front tire and forks off, I could definitely feel the notchiness that was present. I changed the bearings and adjusted according to Mike Nixon's procedure and have never felt that wobble again. I have taken my hands off the bars at all ranges and she tracks quite well with absolutely no wobble, shake or shimmy.

28,000 miles later and all is still well. I like to think that I have become a much better rider on my '82 during this time and have become quite confident on how to handle this machine. I now believe that this is not a bike to take out once in awhile and expect great handling. She needs to be rode often to feel the nuances and seems to be very sensitive to my weight placement and how I pack my gear. Last year I played around with changing the handle bar positioning. Rode for a few weeks with them fully forward and a few weeks with them as far back as they would go. The latter was not good as I lost the feel of the front end and felt like the front was not rooted. All the way forward was fine but put just a smidge more strain on my back and arms. In the end I opted for a little bit less than all the way forward having found a nice compromise between comfort and weight/pressure (the watermelon) on the front. She rides great and responds well to my inputs.

This year, I am riding with a fork brace installed and am still on the fence as to whether I like it or not. I defintitely feel the difference. The input from the front now feels slightly more harsh and just a little chattery over the bumps. Not sure why this is so. I do believe I ride on the worse roads in the country here in Buffalo so I am always trying to improve the handling whle maintaining stock appearance.

Just my :twocents-02cents: .

Patrick
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rpleines
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Re: Handling question.

Post by rpleines »

Frame bracing pictorial. Bracing referenced ealier by Jeff.

http://www.cbxclub.com/Xpress/200303_05.pdf

:text-yeahthat:
Rich Pleines

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