Kawasaki Vulcan Forum banner

1 - 20 of 22 Posts

·
Registered
Joined
·
47 Posts
Discussion Starter #1
OK, I have the 9 all fixed, retitled, registered, and I've been riding it for nearly a week.

As I get more used to it, I'm finding a little wobble in the front end.
If I barely hold just one handgrip, I get a definite wobble, even at slow speeds like 30 to 40 mph. Haven't tried hands free yet, but I from the way it feels, it would surely wobble then too!
And when I encounter a road seam, or a crack in line with the road, there is a little wobble from the front end.

It's almost like a death wobble, but can easily be damped out just by having both hands on the bars. But it's definitely there. I haven't tried letting the wobble build up more, not sure when it would stop, or if!

I've checked for a loose triple tree, headset, wheel bearing, axle, sloppy forks...all seem to be good and tight. Also checked for loose spokes, but I didn't actually check the torque on each and every spoke. After all, this bike has but 2,900 miles on it. It is a salvaged vehicle, but I did speak with the original owner, it basically tipped over at 2 mph, never actually hit anything.

Questions:

1. Anyone else experience this behavior?
2. Anyone have a possible cause?
3. Could tire pressure, or maybe tire type or condition cause a wobble?

At this point, it's just an irritation, but I don't want it to get out of hand.
 

·
Registered
Joined
·
3,881 Posts
Air pressure can cause it, cupping of the tire, loose steering head bearing, may only need the slightest bit on tighten. Is it possibly tire balance? Also the rear can cause this, also tire pressure, and swingarm bearings, but at this low milage dout it. Start with front tire pressure and check close for cupping on the sides, usually the left.


Sent from Motorcycle.com Free App
 

·
Registered
Joined
·
370 Posts
If the front rim is not bent or out of round, and it sounds like it isn't.
Then I would say its either out of balance or tyre is causing it.
To wobble at that low speed the balance would have to be out heaps, balance is easy to check yourself.
My original Dunlop front tyre used to cause a lot of wobble on certain corners at higher speeds, since I got rid of that tyre the bike has been rock solid. Also check the tyre does not have any separation in case, (lumps or bumps or bulging)
 

·
Registered
Joined
·
47 Posts
Discussion Starter #4
Good points, guys...I didn't think about the rear tire/swing arm.
I'm going to head out back to the parking lot now, and check the tire for any bulging, etc.
I never got an owners manual...what is the proper front and rear tire pressures?
 

·
Registered
Joined
·
47 Posts
Discussion Starter #5
OK, I looked at the tire pressures listed on the belt guard...front should be 28 psig, rear 32.
I had 20 Psig and 24, respectively. That could definitely make the front produce a mushy wobble, which is how it felt. I pumped the tires up to the recommended values.
That could make quite a difference, I'll find out on the way home tonight...
 

·
Registered
Joined
·
536 Posts
OK, I looked at the tire pressures listed on the belt guard...front should be 28 psig, rear 32.
I had 20 Psig and 24, respectively. That could definitely make the front produce a mushy wobble, which is how it felt. I pumped the tires up to the recommended values.
That could make quite a difference, I'll find out on the way home tonight...
I had to pump mine up to the 40PSI max to get it to stop the wobble. I would just work my way up until it stops. 20 is definitely too low if it has a wobble that's most likely why. I think the brand of tires seems to make a difference too. I bet by 36PSI it will probably go away.
 

·
Registered
Joined
·
228 Posts
I literately was just going to post the same thing when i say front end wobble.

My wobble started after I put to much air in my front tire. My tire was a little low so I filled it. I took off and at 35 mph my bars started wobbling out of control. Stupid me had no air gauge to check at home. When i went to check the pressure there was 20 more lbs then I needed to have. Removed the air and back to normal.

point of the story.. get a air gauge at my house...
 

·
Registered
Joined
·
47 Posts
Discussion Starter #8
I pumped front up to 28, rear to 32, just like the tag says...It's still there, the wobble, that is.
I think I have the OEM front tire...I'll have to go out in the driveway to see.
Is the OEM tire known to do this???
 

·
Registered
Joined
·
536 Posts
I pumped front up to 28, rear to 32, just like the tag says...It's still there, the wobble, that is.
I think I have the OEM front tire...I'll have to go out in the driveway to see.
Is the OEM tire known to do this???
What is the maximum PSI shown on the tire?? I would say go up to the max a few pounds at a time and see when it stops the wobble....I wouldn't go up past the max if it doesn't stop the wobble....I would start shopping tires if the front end and steering head is properly torqued down and the tire is in balance and wobble still there. Do a search here about front end wobble and you will see lots of posts and solutions.
 

·
Registered
Joined
·
47 Posts
Discussion Starter #10
What is the maximum PSI shown on the tire?? I would say go up to the max a few pounds at a time and see when it stops the wobble....I wouldn't go up past the max if it doesn't stop the wobble....I would start shopping tires if the front end and steering head is properly torqued down and the tire is in balance and wobble still there. Do a search here about front end wobble and you will see lots of posts and solutions.
Thanks Mr. wiz,

I never even thought to search for a wobble thread...I thought I was the only one!
I also have a couple of coil sprung Wranglers (it's a Jeep thing) and they are extremely prone to Death Wobble.
But I never imagined it might be common on a modern bike.
 

·
Registered
Joined
·
47 Posts
Discussion Starter #11
OK, so I searched and read last night for quite a while.
It seems most wobbles are solved by tightening/replacing the headset bearings, and/or replacing the front tire.

Anyone have a torque spec for the headset tightening torque??
 

·
Registered
Joined
·
536 Posts
A wise man once told me..."In theory, practice and theory are the same. In practice, they aren't. Without data you are just another guy with an opinion". That being said, I have a theory about this problem based on my practice but I have no real data to back it up so I am just that guy with an opinion I guess. So take this with a grain of salt but...I am running a stock size Pirelli MT66 on the front of my Classic. It had the wobble so I aired the tire to the maximum and it went away. While on a trip in which I was doing 500 miles a day I was on day 5 and the wobble came back....naturally I thought the tire was low again and I went to air it up and I realized it was still near the 40PSI max. When sitting still I could move the handlebars back and forth quickly and it was as if the tire sidewall was very thin and flexing a lot. I double checked the axle was tight and realized that I think the heat had the softening effect on my sidewall strength due to the fact that it was about 100 degrees and I had been riding for hours so the tires were very hot. Is it possible that heat will effect the sidewall strength of some tires enough that they can wobble and people don't realize its the heat and that more air pressure holds it rigid enough to not flex? I think maybe so. I think this is what was happening in my case. I ride in 100+ degree heat often in my area and I will see what happens this winter when it cools down to more normal temperatures. Just saying.
 

·
Registered
Joined
·
47 Posts
Discussion Starter #14
Thanks for doing my homework for me, Mr wiz.

You may be on to something with your tire softening theory.
I happen to own a industry leading R & D company (Mohawk Innovative Technology, Inc) and we work with structural and rotor dynamics every single day.

All structures, whether single components or built up assemblies, have a natural frequency at which they will resonate, often many frequencies, depending on the particular mode shape.
The front end of this bike is free to oscillate from left to right, consider it as a torsional spring, with the stiffness derived from the tire to road friction, the tire stiffness, the stiffness of the forks, triple tree and so on. If the natural frequency is properly damped, it will respond to a stimulus in a predictable, decaying motion. If the system is underdamped, then it can become unstable, where a small input (vibration from road, tire imperfections, residual imbalance) can be amplified and self sustaining.
In this case, just the contact from your hands provides enough damping to keep the system stable...but remove that damping, and, well, we know what happens.

So what's the solution? Either remove all excitation (not practical) or provide adequate damping. Apparently, the drag from a properly torqued headset bearing is enough to stabilize the system, as long as there is only a normal amount of excitation.

In the case of your hot, soft (maybe) tire, your system appears to be borderline stable, remaining so only if the excitation forces remain below a certain level. Perhaps yes, your tire heats up, softens a bit, and provides enough excitation to require more damping than your headset can provide.

Or maybe, in the continued heat, other parts of your system effectively softened...the forks sliders are aluminum, your fork tube steel. The differential coefficients of thermal expansion work to develop addition clearance, effectively softening the torsional stiffness of the forks.

Anyway, this is the sort of stuff I ponder and experiment with every day...
I do like puzzles, but not while they're hurtling me down the road at 70 mph!!

When I get some time this weekend, I'll check the headset bearings for looseness, and I'll report back.
 

·
Registered
Joined
·
536 Posts
Stripperguy...that was an amazing description of what I thought was going on. The flexing was mostly in the tire as I could actually see it...but could have been amplified by the other factors as well. I look forward to your report of the headset bearings. I never did check mine since I could see the tire flex and it was able to be corrected with air pressure originally and has been fine since tires cooled down.
 

·
Registered
Joined
·
5 Posts
OK. I also bought my 900 wrecked. Apparently he was teaching his girlfriend to ride, at least thats what he told me. wrecked it a low speed in the parking lot. matching me 880's. had the exact same symptoms as you. i thought a fork was bent or the tree bearings. but I replaced the front tire with an avon cobra 90/21 which is the same size the metz was. PROBLEM SOLVED!!!!!!!! Has never rode smoother straighter or handled better and now i can let go of the bars with no wobble.
 

·
Registered
Joined
·
47 Posts
Discussion Starter #17
OK. I also bought my 900 wrecked. Apparently he was teaching his girlfriend to ride, at least thats what he told me. wrecked it a low speed in the parking lot. matching me 880's. had the exact same symptoms as you. i thought a fork was bent or the tree bearings. but I replaced the front tire with an avon cobra 90/21 which is the same size the metz was. PROBLEM SOLVED!!!!!!!! Has never rode smoother straighter or handled better and now i can let go of the bars with no wobble.
It seems the system is borderline stable...swapping tire type is enough to reduce the input excitation.
If you think about tire construction, the stiffness varies from segment to segment on the tire. The overlapping belt construction has some areas that are stiffer, some that are softer. Most of these variations are invisible to us under normal inflation pressures.
But, with possible belt breakdown, fatigue of the rubber compounds, lack of damping in the system, it doesn't seem to take too much to set the system unstable.

If the headset bearing torque doesn't fix it, I'll surely look into an alternate tire.
Thanks for the shared history, lordericmetal.
 

·
Registered
Joined
·
47 Posts
Discussion Starter #18
I laid my hayands on the spanner nut and healeduh!! (apologies for my lame faith healing attempt)

It was just that simple...the spanner nut that preloads the headset bearings was definitely loose...it took 1/4 turn just to take up the free play, and a tiny bit more to get the recommended torque. Pinch bolts on the upper trple clamp were a tad loose too!

I just got back from a quick test ride and it is a changed machine!
No more wobble, not even any botheration over road seams.
I even went no hands at various speeds (I know...please don't preach) and there is absolutely no instability!

I am one happy guy.:D:D:D

Thank you all who responded...this whole shared knowledge thing of the internet and this forum specifically is amazing!
 

·
Registered
Joined
·
536 Posts
Wow. Good stuff. I am surprised that you weren't hearing a clunking sound on bumps with a 1/4 turn of slack in there. I am going to have to check mine at my next maintenance shutdown...uh oh. I retired and moved to a climate where I can ride year round. When do you do maintenance when it's sunny 300 plus days a year. Lol
 

·
Registered
Joined
·
47 Posts
Discussion Starter #20
Wow. Good stuff. I am surprised that you weren't hearing a clunking sound on bumps with a 1/4 turn of slack in there. I am going to have to check mine at my next maintenance shutdown...uh oh. I retired and moved to a climate where I can ride year round. When do you do maintenance when it's sunny 300 plus days a year. Lol
Mr. wiz,

With the bike as heavy as it is, I suppose all my jiggling and tugging couldn't unload the lower bearing enough to expose the loose bearings. Even though the front forks don't have that much travel, they have enough to prevent getting the front wheel off the ground.
If I had put the bike on one of my S-I-L's bike stands, the sloppy bearings would have showed up immediately.

Family and I did a whirlwind tour of Utah a few years ago...but we never made to St George's...but all in all, we all loved the climate and geography there, and of course, the skiing is fantastic!!
I'm tethered here (for a few more years) by my business, family and the Adirondacks. I spend a lot of time in the wilderness areas, hiking, paddling, back country skiing...literally millions of acres of wilderness, thousands of lakes and ponds. It is tricky to carry a couple canoes with the 9!!
 
1 - 20 of 22 Posts
Top