High speed wobble

[sdt354]

MOST VIOLENT WOBBLE TO DATE​

I rode conservatively for 4 hours yesterday. No wobble at all.

But I rode to work today and the wobble showed itself... many times. EVERY TIME in two corners, hitting a couple known dips in the road, at steady speed - about 65 MPH. So not necessarily only during acceleration. There is one area (location of my previous wobble video) that is notorious for generating a wobble. It's a bumpy road with some issues in the road surface. But it's long, straight, and open - hard to not hit the throttle.

So today I hit it, and when I reached about 70 or 80 MPH the beast immediately started a VIOLENT wobble. I don't know the proper way to respond other than "white-knuckling" the handlebars and riding it out. But today was different. It was bucking so hard, it bounced vertically OFF THE ROAD. It was very literally like riding a bucking bronco. It was all I could do to keep it vertical, but I did. I could feel both tires leave the pavement a couple times. I was all over the place, but didn't crash. That was just crazy.

The strange thing is that it's not consistent. Some days are better than others. Today was CERTAINLY a bad day!

I'm left with nothing else to check, and nothing else to change other than major components like swingarm, frame, or forks.

One thing is consitent - No wobble on a flat, smooth surface... like the drag track.

Between all of us, we should be able to help you find the culprit. That's dam dangerous. I'm glad you kept it shiny side up. Just for the hell of it, though you might have done this already. Pull the back tire and shocks and shake the swing-arm around. Make sure the adjuster bolt is centered in the bearing. I've see that happen, where it wasn't in right. Will scratch my noggin on this. I'm sure someone else will to.
Steve-o

 

[Miles Long]

When on a bumpy road, does the shaking start at about the same speed (65-70 mph)? But not on a flat road?
If so, I think that I understand what your problem could be.
Cheers!

 

[Lotsokids]

When on a bumpy road, does the shaking start at about the same speed (65-70 mph)? But not on a flat road?
If so, I think that I understand what your problem could be.
Cheers!

Yes, it starts consistently about the same speed. Please elaborate...
When I'm riding about 60 MPH, if I "flick" the handlebars, it "feels" very weak and "wobbly" in the front between the bars and the tire... somehow. It flexes readily. But remember I installed a super thick steel fork brace and new steering head bearings and races. It's a later model also, so it has the thicker fork tubes. I have no more ideas.

 

[Hamkaas]

I have had the high speed wobble too. It is gone since I have installed an enhanced swing-arm.

send from my mobile phone using Tapatalk

 

[Miles Long]

Yes, it starts consistently about the same speed. Please elaborate...
When I'm riding about 60 MPH, if I "flick" the handlebars, it "feels" very weak and "wobbly" in the front between the bars and the tire... somehow. It flexes readily. But remember I installed a super thick steel fork brace and new steering head bearings and races. It's a later model also, so it has the thicker fork tubes. I have no more ideas.

The rotational speed of your front tire/wheel at the mph in question (60-70) is "exciting" the first resonant frequency of the bike's front end assembly (wheel, tire, forks, trees, handlebars - everything supported by the headstock bearings).
Resonant frequency (often called "critical speed") excitation can be dealt with in four ways -
- change the speed of the exciting force
- stiffen the assembly to raise the resonant frequency
- add mass to lower the frequency of the assembly
- dampen the assembly
Professor Miles Long
Cheers!

 

[Redbone]

The rotational speed of your front tire/wheel at the mph in question (60-70) is "exciting" the first resonant frequency of the bike's front end assembly (wheel, tire, forks, trees, handlebars - everything supported by the headstock bearings).
Resonant frequency (often called "critical speed") excitation can be dealt with in for ways -
- change the speed of the exciting force
- stiffen the assembly to raise the resonant frequency
- add mass to lower the frequency of the assembly
- dampen the assembly
Professor Miles Long
Cheers!

Nice Miles! Your the total package... good looks and a mighty talented brain! Professorship looks good on you! :worthy:

 

[Miles Long]

Nice Miles! Your the total package... good looks and a mighty talented brain! Professorship looks good on you! :worthy:

Thanks, Brian, but ya gots t'know.....
I got my degree from Trump University:confused2:

 

[Redbone]

Thanks, Brian, but ya gots t'know.....
I got my degree from Trump University:confused2:

I just knew you had some blue blood Republican training in ya! :eusa_dance:

 

[Lotsokids]

I just adjusted the head bearings again. After I replaced the head bearings and races a few months ago, I adjusted it using the "bounce" method as I have no other way to torque it. I tightened the head until the bars didn't even go to the stop, much less bounce off them. But no low-speed weave (the result of over-tightening). So I turned the nuts tighter about the thickness of one space on the nuts (if you see it, you'll understand). Maybe 1/4 inch. I can tell I am close to a low-speed weave, but it's good. Rode hard today - even in the known bad areas. No dramatic wobble, but it's there very slightly... I can tell.
Next step is to eventually change both tires (getting worn) and maybe the rear swingarm bearings.

 

[Lotsokids]

I just returned from a business trip and brought back a new set of swingarm bearings.

I'll keep you posted when I install them. Might be a while - other priorities now.

 

[Lotsokids]

Resurrecting this topic again.
Last Saturday I had another extremely violent wobble. Same bad road area, same acceleration. Front tire pressure was a little low. I tightened the steering head more. Now I'm about 1/4 turn tighter PAST the "bounce test" procedure. No low-speed weave, though.

Handlebars a factor?

When I tightened the steering head I turned the bars and noticed the bars flex a little. When rotated to the stop, I could bend the bar a little with my hand. Maybe they are cheap bars, but certainly not strong. I wonder if there could be a resonant "twisting" between my hand grips and the front tire during hard acceleration, shifting, and bad road.

I installed a brace on the handlebar from my son's dirtbike. The ride to work this morning seemed firm. The ride home at that bad part of the road will tell if there is a noticeable difference.

Thoughts?

 

[Bill Seward]

Probably the vibration isolators in the riser. I believe they're rubber mounted. If you could bend your bars at full lock, I don't want to arm wrestle you!

Maybe the bars do flex. I've got drag bars, being so short, there isn't a lot of leverage to bend them. I'm getting new bearings, brakes, and tires put on even as I write this.. I was developing a wobble about 40mph, trailing throttle. Hopefully the new All Balls bearings will help. The Shinko on front (120 size) was cupped a bit. We'll see how it works with everything new..

Hope you made it home OK!

 

[Lotsokids]

If you could bend your bars at full lock, I don't want to arm wrestle you!

Yes, the bar bends at full lock. Not much, but it bends very slightly. Maybe 1/2 inch at bar end. This is independent of the other side obviously.

Hope you made it home OK!

Yep, made it home safely. It felt much more stable... but not 100%. It was VERY windy during my ride home. I pushed acceleration at the "bad road" known wobble area, but didn't push to the max. No wobble. I'll give it some time, but I think I'm on to something.

 

[Bill Seward]

Keep us posted!

 

[kalbo]

On the subject of 'fork brace', I thought the Vmax has a brace as standard, as part of the front fender assembly? Is there another better one available?

 

[Lotsokids]

On the subject of 'fork brace', I thought the Vmax has a brace as standard, as part of the front fender assembly? Is there another better one available?

Yes, one comes standard. I bought a VERY THICK steel one to try to cure my wobble, but no effect.

The brace I recently mentioned is attached to the handlebars. Similar to this:

 

[Lotsokids]

P.S. - My bike seems much more stable now. I'll ride it for a couple more weeks and see how it goes.
I still have new swingarm bearings sitting on my bench waiting for install.... sometime.

 

[Traumahawk]

I chased a wobble for years. Everything that I had tried made it better....but it was still there. It wasnt until someone was behind me in a sweeping curve, and they could SEE the swing arm moving around.

Changing the swing arm bearings solved mine. ( PLUS the bearings were loose when I went to change them).

 

[Bill Seward]

I did swing arm bearing replacement at about 100,000 miles. They were loose!

 

[Lotsokids]

I did swing arm bearing replacement at about 100,000 miles. They were loose!

I torqued mine few months ago. They seemed close. I still intend to change them sometime... when I have time.