front end chatter...

[rojoracing53]

If you know what your doing and can easy into it then you can hard chatter a bike pretty bad and still have a cushion before tucking the front. If your bike is pourly setup like my bike as in way to soft then it will chatter very eary in its potential traction so its easy to control. But for example if my fine tuned R1 superbike chattered at all I was already past the limit and I would be aleady trying to save it from crashing. When I raced chuckwalla my 250 had hard chatter in "every" corner so I'm rather comfortable with controlling it but I will say its rather annoying and does kill some of the fun after awhile.

Oh and chatter doesn't only happen going into the corner while hard on the front end. The 250 would chatter through the entire turn from initial tip in, though the apex and while I was full throttle through the sweeping corners at full lean. The chatter would cease only after I got the bike unloaded from the turn and rather vertical.

[csmith12]

Depends on feel, corner and but basically one of 3 things

Front - (most everyone agrees on these)
Continue throttle roll and loosen up on the bars

Take control by doing nothing. Twist of the Wrist II

Rear - (this is where it gets into gray area per rider)
Loosen up on the bars (most everyone agrees here)
If it's mild, just ignore it or be loose again (most everyone agrees)
Some say, throttle modulation
Some say a touch of rear brake does the trick (you hear it as "settles the chassis")

[Me]
I prefer a smooth roll off and/or upper body goes farther forward and head down even more (Everyone has heard of kiss the mirror but what if your already there? Then try to stick the bar in your ear lol)
[/me]

[Motofool]

Thank you both !!!

[Motofool]

Originally Posted by choneofakind

Wouldn't that also be a function of the damping? Adding more damping would slow the movement of the suspension.

Link to original page on YouTube.

"In classical mechanics, a harmonic oscillator is a system that, when displaced from its equilibrium position, experiences a restoring force, F, proportional to the displacement, x:

F = -kx

where k is a positive constant (spring rate).

If F is the only force acting on the system, the system is called a simple harmonic oscillator, and it undergoes simple harmonic motion: sinusoidal oscillations about the equilibrium point, with a constant amplitude and a constant frequency (which does not depend on the amplitude).

If a frictional force (damping) proportional to the velocity is also present, the harmonic oscillator is described as a damped oscillator. Depending on the friction coefficient, the system can:

Oscillate with a frequency smaller than in the non-damped case, and an amplitude decreasing with time (underdamped oscillator).

Decay to the equilibrium position, without oscillations (overdamped oscillator). (Ideal case of our suspensions, but fixed.)

The boundary solution between an underdamped oscillator and an overdamped oscillator occurs at a particular value of the friction coefficient and is called "critically damped.""

http://en.wikipedia.org/wiki/Harmonic_oscillator

Note that, as described by others, chatter are rapid vibrations of little amplitude, mainly at the contact patch level.
I believe that more damping would help (maybe at the cost of packing up the suspension for other conditions (fourth case in the video)) up to some point, beyond which the tire and tire pressure and quality of the suspension system would have major role.

Old bikes with bias ply tires and two shock absorbers for the swingarm in less than perfect conditions were prone to chatter on curves with some pavement ripple (inducing a pronounced side walking of the rear tire toward outside the turn).

A loose pivot, less than full oil or worn internal valves were more than enough to allow some small non-dampened up-down oscillations.
The temporary cure was reducing pressure in the rear tire.

[Dmented]

Originally Posted by rojoracing53

Oh and chatter doesn't only happen going into the corner while hard on the front end. The 250 would chatter through the entire turn from initial tip in, though the apex and while I was full throttle through the sweeping corners at full lean. The chatter would cease only after I got the bike unloaded from the turn and rather vertical.

EXACTLY!
that is how mine likes to act... but i've slowly been getting rid of it.

I hope you get your bike sorted soon. you already know you're due back at chuckie.

[cuong-nutz]

I found two interesting videos about rear end chatter

Link to original page on YouTube.

Link to original page on YouTube.

Second video, you can see the rear tire of the second rider leave the ground as he's hard on the brakes. When the tires catches the ground, chatter starts and continues through. You can see in in the rear and front suspension.

I don't think we (ninja 250s) would ever encounter rear end chatter since we are do not put a lot of power to the ground but then again, I have not encountered or don't think I have on the tracks I've been on here in Texas.

[rojoracing53]

I wish suspension was just a simple science we could solve with calculations and it is for the most part. Then you introduce the human factor and it becomes an art form with no correct answer and only vague guidelines for reference.

Damping from my 250 is from the suspension completly bottoming out and thus the tire becomes my suspension and the last I checked tire manufacturers don't make good suspension parts . More dampening would only delay my chatter then most likely make it even worse.

[Motofool]

Originally Posted by cuong-nutz

I found two interesting videos about rear end chatter
.........Second video, you can see the rear tire of the second rider leave the ground as he's hard on the brakes. When the tires catches the ground, chatter starts and continues through. You can see in in the rear and front suspension.

Amazing vids, Cuong !!!

You can see that the tire does more for the up-down movement than the suspension; then, it is transmitted to the front tire.

Originally Posted by rojoracing53

.........the tire becomes my suspension and the last I checked tire manufacturers don't make good suspension parts ..........

Compressed air acts just like a spring, no damping here (there is some from the internal friction of the carcass as it gets deformed). (First and second cases in video of post #84 (2:40))

May that be the root of the chattering?

[cuong-nutz]

Originally Posted by Motofool

Amazing vids, Cuong !!!

You can see that the tire does more for the up-down movement than the suspension; then, it is transmitted to the front tire.




Compressed air acts just like a spring, no damping here (there is some from the internal friction of the carcass as it gets deformed). (First and second cases in video of post #84 (2:40))

May that be the root of the chattering?

Sorry, have not looked at the video, but at lean angles hard on the brakes (into the turn--front tire) or hard on the gas (exiting out of the turn--rear tire) If the tire slips from loss of traction, the suspension will extend to try and keep the tire planted on the ground (rebound). When the tire grips again, the suspension is forced up (compression).

It gets tricky right here when turning to get rid of the chatter at mentioned in the video about "chatter explained" since suspension works 100% as it should when it is upright and not leaned over at an angle. Either way you would still adjust rebound and compression to alleviate the situation you are encountering. I would think that most suspension tuners tune the bike to the demands of what the rider experiences in the turns since that is where most time is gained or loss in a race. More traction and power to the ground translates to faster lap times in most cases.

Fast rebound: wheel returns to the ground too fast and tire bounces up (chatter po-goin')

Slow rebound: bike squats, runs wide out of turns since front forks are extended.

soft compression: same thing as a slow rebound.

hard compression: rough riding as the rear kind of just jumps over bumps and just gets worse when you go faster as the rear end doesn't want to squat.

[csmith12]

What do you mean by squat? On a sportbike under ideal conditions, the rear of a bike doesn't squat under throttle application, it rises...

[cuong-nutz]

Originally Posted by csmith12

What do you mean by squat? On a sportbike under ideal conditions, the rear of a bike doesn't squat under throttle application, it rises...

The rear does squat while the front rises under power. Think of power wheelies. Think of when you chop the throttle and get back on the gas hard.

edit: You are essentially right, Chris: http://www.suspact.com/Anti_Squat.html

I've learned a lot about suspension from off-roading trying to build 4 link and 3 link suspension

[alex.s]

whats a 4 link suspension on a bike? like the britton?

[burningscooter]

Originally Posted by Rexbo

Moar throttle

This is the correct response.

[rojoracing53]

Here's what I did to get rid of my chatter
http://www.ninjette.org/forums/showt...200#post695200

[KazMan]

Originally Posted by csmith12

What do you mean by squat? On a sportbike under ideal conditions, the rear of a bike doesn't squat under throttle application, it rises...

I see what you did there