Front tire bounces at lower speed


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Bryancga
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Front tire bounces at lower speed

Postby Bryancga » Mon Oct 01, 2012 6:13 am



Hello,
I am new to Goldwing Docs, I'm 51and have been riding MC's since my teens .
I purchased a 82 Gl 1100 with 43,000 miles this past spring and had new brakes, fork seals, along with new tires they are M/N Shinko 230. Unfortunately the front tire bounces at speeds of 45 and below, it reminds you of a warped
rotor on braking car. I took it back to the shop that installed the tires they said that the balance of the tires
were fine and that we needed to replace the fork springs I disagree with them, my theory is that if the fork springs were bad
they would bounce at all speeds. I had another independent bike mechanic check it out and he said that front tire has a flat spot.
I don't know what direction to go with this problem .Any suggestions will be appreciated

Thanks Bryan



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Re: Front tire bounces at lower speed

Postby virgilmobile » Mon Oct 01, 2012 7:13 am

It is possible the tire is not seated on the rim properly,the rim is bent(even the cast ones),fork slides worn and the forks are seizing,defective casting on the tire,bent fork,etc.
I would center stand it and jack the front end up just enough to get the wheel off the ground.
turn the wheel and watch the rim(both sides) and the tire(at the bead and tread) to see if there is any "out of round"
I did have a 83 that hit a curb so hard that it bent the rim in one spot and bend one fork 0.035" out of true.
It took a while to find that.I had to tear the whole thing down and inspect every part.
I also threw away the weights and use balancing beads in the tires.

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Re: Front tire bounces at lower speed

Postby WingAdmin » Mon Oct 01, 2012 10:01 am

If it IS the suspension causing the bouncing (and not the tire), it is likely not the springs, but the dampening system (fork oil/dampers) causing the problem.

Undamped springs will bounce, and this will usually happen at a specific speed range, as you approach the resonant frequency of the wheel/springs. You can often see this on cars that have broken/failed shock absorbers on the highway - the wheel will be bouncing so violently that it becomes a blur, bouncing a few inches up and down. I often wonder how people can continue to drive their cars this way - it's supremely dangerous!

In any case, the job of the dampers and fork oil inside the forks is to slow the movement of the suspension, to prevent vibration similar to what you're experiencing.

Is it more of a shimmy (side to side) or a vibration (up and down) that you're experiencing?

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Re: Front tire bounces at lower speed

Postby bustedwing » Mon Oct 01, 2012 10:23 am

While you have the bike up on the center stand, plade a block of wood next to the side of the tire then spin it slowly and look for warpage, then place the block across the tread and spin. That way you check for runout. Too much of either will caues your problem.
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Re: Front tire bounces at lower speed

Postby dayser7 » Mon Oct 01, 2012 10:43 am

I have had 3 goldwings and some other bikes over the last two years..it has been my experience with everyone of them that at low speeds the front will wobble without hands on the wheel...I guess I just figured it was a low speed thing...

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Re: Front tire bounces at lower speed

Postby WingAdmin » Mon Oct 01, 2012 11:03 am

bustedwing wrote:While you have the bike up on the center stand, plade a block of wood next to the side of the tire then spin it slowly and look for warpage, then place the block across the tread and spin. That way you check for runout. Too much of either will caues your problem.


Good idea - also check the tire itself, for irregularities in the tread. I have seen a tire that was failing internally, and the only indication was a vibration while riding, and the tread deviated slightly from side to side when the tire was spun like he described.

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Re: Front tire bounces at lower speed

Postby bgiff17 » Mon Oct 01, 2012 1:11 pm

I mount and balance a slew of tires here at my shop. recently a customer who has had 10+ sets of tires (mostly shinkos over the last several of years) mounted by me, never had a problem until the last shinko on the front of his fjr. he described your symptoms exactly. i re-checked the tire balance, it was spot on. it appeared ok spinning on the balance machine. he eventually put on a new shinko...problem went away. it was the tire, i still don't know what the cause was, couldn't see a problem. maybe a belt separation or slight irregularity???

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Re: Front tire bounces at lower speed

Postby scotterichmond » Mon Oct 01, 2012 2:01 pm

you know,
you can have a tire still be in balance with two heavy spots . one because of the tire and one made by wheel weights. then it goes "plop plop plop".

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Re: Front tire bounces at lower speed

Postby Bryancga » Mon Oct 01, 2012 8:43 pm

WingMan
It is definitely a up and down bounce not a shimmy.It also gets more pronounced after you have road on it.I'm assuming the heat
from the travel is the reason for this.
How do you check your damping system? The fork oil was replaced the same time as the fork seals.

bgiff
I was trying to avoid buying a new tire. Have you ever tried tire balancing beads?

Virgilmobile
In your post you said that you got rid of the wheel weights and went to tire beads? What are thoughts on them
Pro's and Con's.
Thanks Bryan

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Re: Front tire bounces at lower speed

Postby RoadRogue » Mon Oct 01, 2012 9:38 pm

Dyna Beads are the way to balance your tires period. I use them in both of my wings and trailers too.
Your bouncing tire sounds to me like a bad tire. Maybe the shop you got it from will replace the tire for you no charge if the new one solves the problem. You shouldnt ride it the way it is. They sold you a tire and did the work and your bike isnt right. I assume it was OK before you took it in. give them the chance to make it right 8-)
Ride safe, Todd
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Re: Front tire bounces at lower speed

Postby Bryancga » Mon Oct 01, 2012 10:00 pm

RoadRogue
I have given them several opportunities, I just gave you the short verision of my dealings with them.They said it is fork spring that need to be replaced not the tire.I will not be returning to this shop, I think my next move will either be tire beads or a new dunlop. How difficult is it to put in the beads?

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Re: Front tire bounces at lower speed

Postby RoadRogue » Mon Oct 01, 2012 10:14 pm

The beads are a piece of cake to install. they come with a bottle and hose to install them. Remove the valve core forom the valve stem, once all the air is out ,using the applicator bottle you just "pour" them in. Reinstall the valve core, air the tire up and ride. Oh yes you should remove all lead wheel weights from the rim.

heres a link to the how to article on installing the beads 8-)
viewtopic.php?f=11&t=1662
Ride safe, Todd
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Re: Front tire bounces at lower speed

Postby Bryancga » Tue Oct 02, 2012 6:10 am

RoadRogue
Thanks, I see that there are several different types of beads is one better then the other?

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Re: Front tire bounces at lower speed

Postby WingAdmin » Tue Oct 02, 2012 10:06 am

Bryancga wrote:RoadRogue
Thanks, I see that there are several different types of beads is one better then the other?


They all work more or less the same. Some are ceramic, some are coated glass. I prefer the ceramic Dyna Beads, they're a bit more dense (heavy) so it takes less beads to do the same job.

I have them in three motorcycles as well as in my truck tires, and have been using them for years now. I swear by them, and will never go back to wheel weights.

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Re: Front tire bounces at lower speed

Postby Bryancga » Wed Oct 03, 2012 8:14 am

I think the balancing beads are my next step .

WingMan
I am still interested in how to check and test the damping system?

I am not completely convinced that my only issue is the tire when you take into account
the age and mileage of the bike. [1982 w/ 43000 mi]
My front fork air pressure is approximately 18 psi and I have new fork oil and seals.

Thank Bryan

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Re: Front tire bounces at lower speed

Postby Bryancga » Fri Oct 12, 2012 6:34 pm

I have installed tire balancing beads and I made a 50mi run, it is a improvment from
the way that it was, but it still feels like the front tire has a flat spot.
Thanks Bryan

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Re: Front tire bounces at lower speed

Postby WingAdmin » Sun Oct 14, 2012 9:42 am

A note virgil wrote above shouldn't be discounted - is the wheel seated properly on the rim? I had a tire that would not seat on the rim for love nor money. When inflated, it looked perfect - the only indication that it wasn't seated properly was that a small molded line on the side was a bit closer to the rim in the area where it wasn't seated correctly. Deflating the tire, it was obvious that it wasn't seated correctly, but inflated, it was almost impossible to tell. Try deflating the tire (careful to have the valve at the top of the wheel, so you don't eject your dyna-beads) and then rotate it to make sure the bead on both sides is properly seated all the way around.

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Re: Front tire bounces at lower speed

Postby Bryancga » Mon Oct 15, 2012 5:07 am

I did look at the tire, but not that close. I'll look closer at the tire.
WingAdmin, how do test your front forks dampening for proper operation?

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Re: Front tire bounces at lower speed

Postby WingAdmin » Mon Oct 15, 2012 10:44 am

Bryancga wrote:I did look at the tire, but not that close. I'll look closer at the tire.
WingAdmin, how do test your front forks dampening for proper operation?


It's actually damping, not dampening. In any case, the purpose behind the damping is to stop the tendency of the fork spring to "bounce." The wheel is moved upward by a bump. This compresses the spring, storing energy. The wheel itself has momentum, so even after it has traveled past the bump, it continues to move upward, jumping up into the air. Eventually the upward momentum is countered by the force of the compressed spring. The spring then expands, pushing the wheel back out. The wheel hits the ground, and being a rubber doughnut with some elasticity, bounces back up. This compresses the spring again. Some energy is lost as heat, both in the spring itself, in the tire, and in the friction of the shock bushings and seals. Eventually the springing back and forth will stop. In the meantime, the wheel has spent a substantial amount of time in the air, not providing traction on the ground. That's not a good thing.

What I just described is a suspension system with no damping whatsoever. You can see that sometimes on a car on the road with a failed shock - the wheel will be bouncing up and down rapidly as the car drives along, usually at highway speed.

Damping adds resistance, but not in a way that stores energy. Oil is forced through small holes - it takes energy to do this, and the energy is converted to heat. So as the wheel moves upward, it is countered by the spring, but also by the resistance of the oil being forced through the holes. This is called compression damping. As soon as the wheel is past the bump, the oil counters the momentum of the wheel, and the spring pushes it back down, to make sure it stays in contact with the road. Not too quickly though - if it shoves it down quickly, the tire will bounce back up again. So instead, the oil is used on the downstroke as well, to dampen the movement of the wheel back down to the road. This is called rebound damping.

Now...how to determine if damping is operating correctly? On a car, it's easy: Press down on one corner, then quickly let it up. If it bounces more than once, you've likely got a problem with the shock, which provides damping.

On motorcycle forks, it's tougher, because you have two separate forks, and they are connected together at the axle. So if one is not damping correctly, it can be hard to tell because they other one may still be working just fine. If both are not damping correctly, you can do the same test as on a car - push down the front, quickly let go, and see if it bounces, instead of just returning to the normal position.

I found this on the web, and it's a very good description of symptoms to look for when diagnosing damping problems:

Lack Of Rebound, Fork
* The fork offers a supremely plush ride, especially when riding straight up. With higher speeds, however, the feeling of control is lost. The fork feels mushy, and traction feel is poor.
* After hitting bumps at speed, the front tire tends to chatter or bounce, and the fork has a wallowy, loose feel.
* When flicking the bike into a corner at speed, the front tire begins to chatter and lose traction. This translates into an unstable feel at the handlebar.
* As speed increases and steering inputs become more aggressive, a lack of control begins to appear. Chassis attitude (sudden changes in pitch) becomes a problem (front-end wallowing), with the front end refusing to stabilize after the bike is steered hard into a turn.

Too Much Rebound, Fork
* The ride is harsh. Rough pavement makes the fork feel as if it's locking up with stiction and harshness.
* Under hard acceleration exiting bumpy corners, the front end feels like it wants to "wiggle" or "tankslap." The tire feels as if it isn't staying in contact with the pavement when on the gas.
* The harsh, unforgiving ride makes the bike hard to control when riding through dips and rolling bumps at speed. The suspension's reluctance to maintain tire traction through these sections erodes rider confidence.

Lack Of Compression, Fork
* Front-end dive while on the brakes is excessive.
* Rear end of motorcycle wants to "come around" when using front brakes aggressively.
* Front suspension bottoms, with a solid hit under heavy braking and after hitting bumps.* Front end has a mushy and vague feeling, similar to lack of rebound damping.

Too Much Compression, Fork
* Harsh ride, especially when bumps and ripples are first contacted by the front wheel.
* Bumps and ripples are felt directly; the initial hit is routed through the chassis instantly, with big hits bouncing the tire off the pavement.
* The bike's ride height is affected negatively; the front end rides too high in the corners; bike may want to drift wide in corners.
* Brake dive is reduced, though the chassis is upset significantly by bumps encountered during braking.

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Re: Front tire bounces at lower speed

Postby virgilmobile » Mon Oct 15, 2012 12:29 pm

This is low tech,but I did have problems with my 1100 front end.After rebuilding,I also questioned about the same thing and found no exact thing to measure.
If the fork has dampening at all,the amount is adjusted by oil weight.
Assuming all the innards are good,standard fork oil used.
On my 1100,the innards were worn so badly that I had to use #30 motor oil to keep the fork from bouncing.
How did I even check it to see if it worked to start with????
I removed the front wheel and everything that attaches both forks together.
I removed each spring.
From there,I lift each slide and pull it back down.
With no oil or damaged valves,it will just slam back to the bottom.
With oil,It has a noticeable drag upward and even more on the downward stroke.
After repairing the control valves( a secret non repairable not listed part),I adjusted the oil mixture viscosity to provide the ride I desired.
Here's 2 videos in this post that show a nonworking shock and one that works.viewtopic.php?f=6&t=10786&start=25

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Re: Front tire bounces at lower speed

Postby Bryancga » Mon Oct 15, 2012 8:21 pm

Thank You, It looks like I have some homework.




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