uncomfortable wobble at 90 to 100

[pamcopete]

travis,

That's my understanding. The big factor is the tires. The author of the book goes into great detail about the dynamics of a motorcycle tire. Very complex.

I'm not sure what the land speed record people do, but those are no ordinary motorcycles and they may be able to do weird things because they do not have to turn or bank. I know that like all very high speed vehicles, the tires are pumped up to some enormous pressure.

Take a quick read of the book. The author shows the pendulum relationship between the front and rear wheels and even says that if the front and rear wheels have the same harmonic frequency, they will basically self destruct when they both start oscillating at the same frequency.

My son had a video that depicted the constant motion of the moving parts of a motorcycle. Everything is moving all the time. Scary.

I'll contact him and see if he still has that video and post it here.

 

[xsjohn]

Mine only wobbles when I may have had one to may to drink......And if I stop and have a couple more I really don't even notice that...........

xsjohn

 

[Travis]

^^ haha! Please tell you aren't really riding with 3 too many to drink.. Wait, I thought you said you don't even drink???

Pete, that video sounds interesting.. Hope he's still got it.

 

[xsjohn]

Travis.......the reason for the extra few drinks is a good one......if you fall down it won't hurt near as bad.............

xsjohn

 

[Travis]

ahh... good thinking john.. but if 3 too many is good, 6 too many is probably better.

 

[Sundie]

land speed guys are a: very careful with their wheel weights and balance, b: have *extreme* caster on the front wheel (more caster = greater stabilty in a straight line, and a larger tendency to *want* to go in a straight line) and either run car tires (which takes the whole issue away) or solid tires (again, takes a lot of the issue away, because of the weight at the edge of the circle acting as a gyroscope)

 

[xsjohn]

There is always round 2 to consider and you sure can't leave without "one for the ditch" can ya..........xsjohn

 

[urbandork]

ill take a read the book and ill take a look at the other items...

... btw the bike is a 77 standard frame

 

[gggGary]

Been waiting to hear what year it was! It should handle those speeds with no issues then. Find the problem. Because there IS a problem.

 

[Sundie]

the only thing i wonder is when you say it's a "frame", have you done significant mods.

 

[gggGary]

Reread your first post did you try setting the rear shock preloads to the lowest (softest)position? How much sack does the front end have? A couple of spacers above the springs cut from PVC pipe can help get the bike back up to stock height. did you check for runout and dents on the wheels? doesn't have to be fancy, center stand and a pencil from fork and swing arm to the wheels will reveal any gross deformities.

 

[gggGary]

Yes cupped tires can cause weave also. Old guy story warning!! Do NOT try this at home. Back in the day road racing a box stock CB900F I found it would start weaving on the front straight at Road America once it was up over a 100MPH or so. Noticed the edges of the front tire tread were cupping. Got out the belt sander and evened up the tread, issue solved.

 

[gggGary]

One more can't hurt to check; an unevenly stretched chain could be the start of a periodic harmonic that other parts may be sympathetic too and chime in to create a "symphony"

 

[inxs]

- sometimes theres nothing quite like harmonics

 

[xsjohn]

If a person can find a way to make the engine vibrate even more then the wobbles might be overlooked ....LOL

xsjohn

 

[xjwmx]

I don't wobble till 150 mph, then I crash. Usually skins my knee and both elbows.

 

[urbandork]

the only thing i wonder is when you say it's a "frame", have you done significant mods.

Kick start only 750 big bore, performance cam valve springs clutch, high ratio primary gear set, Del Lorto phf36 carbs, pod filters, battery relocation, wiring harness simplified, rear lights relocated, Woodcraft clip-ons, Fast from the Past rearsets, xs750 tank, Progressive Suspension 14 series shocks, headlight and gauge cluster lowered, flat black and shaved frame, and cafe style seat modified to fit with xs750 tank.

 

[urbandork]

Reread your first post did you try setting the rear shock preloads to the lowest (softest)position? How much sack does the front end have? A couple of spacers above the springs cut from PVC pipe can help get the bike back up to stock height. did you check for runout and dents on the wheels? doesn't have to be fancy, center stand and a pencil from fork and swing arm to the wheels will reveal any gross deformities.

what is sack? did u mean sag? i was thinking of going with progressive suspension springs while changing the fork oil

Yes cupped tires can cause weave also. Old guy story warning!! Do NOT try this at home. Back in the day road racing a box stock CB900F I found it would start weaving on the front straight at Road America once it was up over a 100MPH or so. Noticed the edges of the front tire tread were cupping. Got out the belt sander and evened up the tread, issue solved.

ill check but i dont think they are cupped

 

[urbandork]

One more can't hurt to check; an unevenly stretched chain could be the start of a periodic harmonic that other parts may be sympathetic too and chime in to create a "symphony"

how do i check for an unevenly stretched chain? or do i just change it?

btw thank for all the advice guys

 

[inxs]

what is sack? did u mean sag? i was thinking of going with progressive suspension springs while changing the fork oil

- you might like to have a think about race-tec emulators...some reading here