V-Max Speed Wobble (ran it up to 115mph and...)

[brian hicks]

I've pushed my luck at around 100Mph with a bad wobble suddenly appearing. Hitting a small bump can suddenly induce it. It becomes nearly impossible to steer in a straight line and if you happen to be overtaking and there's traffic coming in the opposite direction then I believe that death is a very easy outcome.

 

[Pighuntingpuppy]

Well....If everything has been replaced that can be replaced and the wobble is still there, then the one thing that is left is the one part that cannot be replaced without a ton of paperwork. The frame. There has to be a manufacturing defect in the frame or the frame is somehow damaged. Is something a small fraction of a degree off? Does the frame have a small tweak? To get those answers, you need to find the frame specs and start measuring.

These bikes do have weak frames with a powerful engine. One good launch could be enough to tweak the frame and cause problems. I have seen many unibody cars with ridiculously powered engines twist the body going down the track.

Its like fixing a car, if you replace parts and the problem is still there, replacing it with different parts isnt gonna solve the problem.

 

[Coastal Grey]

I have quickly been moving beyond the realm of, as you mention, fairly easy remedies, so yes, it is entirely possible to have a frame issue. I have considered this indeed. I'm hoping I can find a front fork frame brace and get the 93 front-end functional before I run out of riding season but sourcing a brace within budget has proven to be an issue. Either way, I am fast running out of riding season for this year anyway and have many other things to get done, so whatever I do this fall/winter regarding the bike will slow to a crawl and may not involve any ride testing.

Pitch the whole shot and start fresh!
Seriously

 

[Shuriken]

I've pushed my luck at around 100Mph with a bad wobble suddenly appearing. Hitting a small bump can suddenly induce it. It becomes nearly impossible to steer in a straight line and if you happen to be overtaking and there's traffic coming in the opposite direction then I believe that death is a very easy outcome.

This is why it's worth it to me to solve the problem. Not so we motorcyclists can ride unsafely or illegally on the road but exactly the opposite; so that when changing lanes or passing at speed, or when performing evasive actions, the bike remains controllable. In fact, I'd say the number one reason to keep pursuing the solution is for safety.

This video makes me ill. I believe the cyclist survived but this illustrates a violent high speed wobble on the interstate followed by a crash. I am not able to tell what speeds were at play but it looks to me like the rider was hard on the throttle and was at high speed. This is a great reminder for us all that safety comes first:


I may have an option to get another frame and title but as mentioned, there is paperwork involved as well as a lot of time required to swap everything to a new frame. It would be an opportunity to repaint the engine and replace the middle gear boot!

 

[MaxMidnight]

I intend to solve the issue... just waiting for parts to show up. No, I am not happy about the cost involved but I am very satisfied to have found and resolved a variety of other issues along the way.

Apparently, finding 93 and up fork braces are like finding 4 leaf clovers at the end of the rainbow. I love the additional options the 93 and up forks offer regarding brakes. I also love being able to ditch the air crossover tube!

Your efforts are commendable and deserve to bear fruit.
I've come to this thread relatively late and given the number of posts it is difficult to keep tabs on what you have done so far and what was the result.
I've attached what I hope is a fair summary on what's been tried over the years (and yes, I know I should probably get out more).
I'm hoping it will prove useful for anyone wanting to see what you have tried.

Some questions:

• In post #1 you say you have an OEM screen. Is this still on the bike and if so have you tried running without it?
• Do you still have the OEM handlebars? Have you tried lower bars which will move you and the centre of mass forward.
• What size/ profile tyres are fitted and what pressures do you run them at.? How do they compare with OE? (110/ 90-18 & 150/ 90-15 and 33/ 33 psi for loads up to 90kg and 33/ 36 psi over that). Have you run them at these pressures?

Some observations: Have you measured and set the static sag - the front should be between between 25 and 35 mm depending on how you like the feel. Regardless of spring type (Progressive wound or fixed weight) it is adjusted by altering the length of the spacer. If you set it at the lower end additional pre load can be added with washers.
Rear will be between 2 and 8mm and achieved by adjusting the pre-load.
IMO it is essential that you measure this and don't guess as you will have a base number to work with and can measure any changes you make and the effect this has.
Whilst I may well be wrong I think that some of your feelings about the 'sloppyness' of the forks is due to the wrong amount of sag.

I would use the OE spec for oil viscosity and amount.

Head bearing adjustment. I use the process on the attachment. IMO the spring balance is the important item here as I found that the pre-load on the bearing increased when the top yoke centre nut was tightened.
The article also mentions the Furber fix and some info is attached.

Make sure that all fasteners are to the correct spec. This doesn't meant putting a spanner on them and seeing if they are tight. Back them off and then re-torque to the correct spec.
In particular check all suspension, swinging arm and engine mount fasteners. Note the correct torque sequence.

You have done a hell of a lot so far and at some expense. I'm a great believer in the adage 'If it ant broke don't fix it'. I appreciate a drowning man (no insult intended) will grasp at whatever he can. But unless you can establish beyond reasonable doubt that a part is faulty (e.g. your head race bearings, post #87) leave the part be. Don't waste any more time or money than you need to. Above all DON'T GUESS!

If not done so already make notes of what you have done/ intend to do and what the outcome was. In particular where you have gone away from OE spec.

 

[Shuriken]

That is a great summary, Steve! I especially agree with your opinion posted in point #27!

I had planned to soon make a very detailed summary of my work and place it into a table format. You and I had the same idea. I will still get to this at some point because when I fix it to my satisfaction, this entire thread will need a TLDR table summary for anyone wishing to skip to the end. I would like the work to benefit others, not just myself, and a summary such as what you posted will be great.

After all the work and testing I've done, at this point, I surmise that the hypersensitivity I've been describing, which leads to the high speed weave, has been originating in the front end of the bike. Continuing at speed merely increases forces at play and transmits them towards the rear of the motorcycle, into and through the frame, and finally to the rear suspension and wheel. I believe the problem begins individually up front, possibly involving 1 or 2 items, but after getting translated to the rear, becomes a system problem involving more than 1 or 2 items, and which then could oscillate back and forth....

As soon as I can assemble 1) the larger rotors, 2) the bigger calipers, and 3) the nearly unobtanium fork brace, I will be able to take a bigger leap regarding the theories and testing. I do expect that the larger forks (from a well-running 93) will feel different during riding. I haven't inspected springs, oil, oil capacity, etc. yet, but I will. I believe all are OEM and I will start over when the front end is assembled regarding torque, fork alignment and stiction, and measuring front sag.

 

[Tom Determan]

Go back to your "Systems Dynamics" course book (do you still have it?) and reread the chapter on harmonics and mass-damper-spring systems, LOL.

 

[wilks]

Time to “unwatch” this thread….it has officially jumped the shark.

 

[Tom Determan]

Time to “unwatch” this thread….it has officially jumped the shark.

It's getting pretty long in the tooth !

 

[Shuriken]

It's getting pretty long in the tooth !

Yes it is. Thanks for your contributions and input.

 

[Shuriken]

Began inspecting the larger forks. The dimensional differences are telling.

 

[Fire-medic]

The crash video, I couldn't read the speedo readout. It appeared he was racing the white car to his right. At some point, he apparently pulled a wheelie, and the oscillations began when his front wheel came down. That's how I saw it. It looks to be a fairly-new sportbike. I suppose this shows that even a sportbike can develop instability. What isn't known is anything about the bike, how-worn are its tires, previous crash damage not repaired, a bent wheel rim, the possibilities go on... .

The best thing for a rider wanting supreme handling is, get a Gen. II! A Gen. I with Progressive Suspension fork springs, or Race Tech (R.T.) springs (constant-rate and rated according to your needs), R.T. cartridge emulators, RICOR's (wave washer stacks), a fork brace, and best of all, wheels sized for radial tires. Those wheels wearing properly sized and matched tires, too. Cheaper than an USD front fork, in most cases, unless you spot a 'deal.'

 

[one2dmax]

I had a 2005 that went end over end. When I got it here I went and test rode it to make sure that the engine shifted and it was so stable even with the bent forks that I ran that baby up to redline (150) and it was solid. This was with the bent forks and bent handlebar. A wobble would have been bad since one of the sides of the handlebars was almost touching my side to begin with. Made for an awkward ride lol. I would highly advise following my bad choices there but it is what it is lol.

 

[MaxMidnight]

That is a great summary, Steve! I especially agree with your opinion posted in point #27!

I had planned to soon make a very detailed summary of my work and place it into a table format. You and I had the same idea. I will still get to this at some point because when I fix it to my satisfaction, this entire thread will need a TLDR table summary for anyone wishing to skip to the end. I would like the work to benefit others, not just myself, and a summary such as what you posted will be great.

I am of the view that there is no single factor that gives rise to the symptoms that you describe so to allow any meaningful conclusion the variables must be recorded.

A summary will be useful but in addition to detailing the work you have done together with the outcome then (IMO) it is essential that you also document what changes from OE are on your bike e.g. Handlebars, suspension, wheel or tyre size, fairings etc. You would also need to include something about yourself i.e. height and weight as this too could influence the symptoms. It's unlikely that there are many Gen I's in original condition as there will also be a variation in the height and weight of the riders.

I would also group the steps taken such as the changes to steering head bearing tightness and here a reference value would be of help.

 

[retrosdad]

Wouldn’t it be the height of irony if the high speed wobble turned out to be completely caused by an overly flexible frame?

 

[Shuriken]

I had a 2005 that went end over end. When I got it here I went and test rode it to make sure that the engine shifted and it was so stable even with the bent forks that I ran that baby up to redline (150) and it was solid. This was with the bent forks and bent handlebar. A wobble would have been bad since one of the sides of the handlebars was almost touching my side to begin with. Made for an awkward ride lol. I would highly advise following my bad choices there but it is what it is lol.

 

[MaxMidnight]

Wouldn’t it be the height of irony if the high speed wobble turned out to be completely caused by an overly flexible frame?

What, you mean like all Japanese frames of that era?

 

[retrosdad]

What, you mean like all Japanese frames of that era?

Are you offering fact or your opinion?

 

[MaxMidnight]

Yes, you are correct to ask, I should have said most Japanese frames of that era and whose design go back even earlier.

Once again, you are welcome to your opinion as I am to mine.

 

[retrosdad]

Yes, you are correct to ask, I should have said most Japanese frames of that era and whose design go back even earlier.

Once again, you are welcome to your opinion as I am to mine.

Is that “most” fact or your opinion?