Death wobbles on a ZX9

[MrStompy]

Ive been riding around on my bro's 01 ZX9

When you accelerate then cut the throttle and let go of the handle bars the steering starts to shake.
the shake gets worse and worse (if you let it go) it looks like it will become a tank slapper if you leave it go like that. As soon as you grab back hold of the bars it brings it back under control.

You dont really notice it if you keep both hands on the bars though.

it went in for a service today and when i picked it up the guy reckons the discs and bearings are fine. he didnt seem to have a very comprehensive workshop so i am wondering how the hell he could tell if the discs are warped or not.

the only other thing that i can think of is wheel balance but i have no experience of riding a bike with bad wheel balance so i dont know what that would feel like.

has anyone experienced anything similar? or got any tips on what i could check/test.

really its gotta go to a professional to get it fixed but im worried that if this bloke today couldnt diagnose it then maybe other places wont either and will just replace shit till they get it right ie making it very expensive.

PS. the bloke today was a really good guy and seems to have done a good honest job on the service he just couldnt solve this problem so im not dissing him -atleast he was honest with me.

[Rossi]

Sounds like tyre wear to me

BUT why do you want to let go of the bars ?????????????

[Barrabob]

Steering head bearings okay??? Lift the front off the ground by balancing it on the sidestand and turn it lock to lock and see if you can feel notchiness or excesive play in them.

I have other theorys as well owning a slapper model but that would be the first place i would look.

What happens if you try to push it into a corner at speed does it just want to stand up and wobblearound then try to toss you into the scrub.???

Could be too soft in the rear but would check out the steering head bearings first because those 9rs are suposed to be a pretty stable sort of thing.

How old is the front tyre?? And a unbalanced wheel will get a shake up.

[I-K]

Could be too soft in the rear but would check out the steering head bearings first because those 9rs are suposed to be a pretty stable sort of thing.

Keep in mind this is happening when he buttons off, ie. weight transfer *onto* the front wheel... but, yeh, with the 9's being as stable as they are, something's not right here.

As you already said, tyre wear/pressure, steering head bearings... that'll be the place to start.

[FrogZ]

Im betting tyre wear...

[Strika]

Although tyre wear, tyre balance, tyre pressure and bearings can play a part in causing this,(and please check to make sure), for the most part, every motorcycle I have ever owned has done this at some speed. Bikes are inherently unstable by design. At some point the dynamics will find a point where they don't harmonise!!! This is the speed at which the bike will wiggle the bars if you don't have any pressure on them. The speeds will vary bike to bike.

As an example, with new tyres, and as a matter of fact a new bike (the hornet) the Cb used to wobble on deceleration from 80-60kph if you took your hands off the bars.

The E1 9R I have now, has a very slight one in comparison to the Hornet at about 75-65kph.

The CBR600 I had used to do it at 60-50 on deceleration!

However, over the years, I have always found that I very rarely find myself riding around without my hands on the bars, so I tend not to worry about it too much nowadays!

[Gosling1]

....However, over the years, I have always found that I very rarely find myself riding around without my hands on the bars, so I tend not to worry about it too much nowadays!

Exactly ! (shakes head ) - why would you take your hands off the bars in the first place, its not like this is a *normal* riding issue is it ??

The whole point of handlebars in the first place is to stop the front wheel from doing its own thing whenever it likes. Keep your hands on the bars, and I bet you hardly ever get a wiggle on deceleration.....

[Nanna10r]

How else is Stompy going to See how severe the wobble is unless he Removes the "Organic Dampner" from the equation.

I'mk with most it's the tyre or TYRE conbination.

[dave#3]

Has the ride height at the rear been increased, particularly with spacers above the top shock mount ? This will upset the handling (if the front isn't adjusted to compensate) - my old F1 zx9 used to do exactly what you describe and had been raised approx 7 mm.

[MadKaw]

Mine used to head shake too, and it had a damper...

It also had the arse raised 16mm, the front dropped 5mm, 150 hp and ran slicks..... you get use to it...

To be honest, this shouldn't happen on a road bike, not to the degree you describe... Could be the tyres as I had a similar problem on my ZX7R (the most stable soprtsbike Kawi ever made). The cause was chopped out sides of the 207 GP I was running on the front, it had done a couple of track days you see...

Could also be the forks playing up under load. A change of fork oil could freshen the front..

[MrStompy]

Thanks everyone for the input.
to be honest i hadnt even considered tyre wear but it certainly makes sense - especially what Madkaw has described as the tyres on it are just about stuffed from 2 track days.

thats what i love about this forum - you have a problem that has you scratching your head and you put a post in here and people will usually have had a similar experience that solves your prob

[MrStompy]

Has the ride height at the rear been increased, particularly with spacers above the top shock mount ? This will upset the handling (if the front isn't adjusted to compensate) - my old F1 zx9 used to do exactly what you describe and had been raised approx 7 mm.

the suspension and ride height is standard as far as i know. it could probably do with a service on it though.

[MrStompy]

Sounds like tyre wear to me

BUT why do you want to let go of the bars ?????????????

after what i have read here i agree it is probably tyre wear too.

i dont want to let go of the bars.
a while ago i notice a strange wobble but i didnt bother to try recreate the problem at that time. the next time i rode it i tried to see if it was still a problem and to work out steps to recreate the problem. Taking your hands off the bars after decellerating is the easiest way to repetively see it do it.

you probably wouldnt notice this through normal use but the fact that it didnt always do it is a reason to find out why it is doing it now.

[ty]

I'm betting on tyre-wear too.
I had similar symptoms when the front tyre got scalloped - uneven wear.
ty

[mike-s]

Sounds like tyre wear to me

BUT why do you want to let go of the bars ?????????????

Agreed, had that happen to my old gpx. also it quirmedlike hell when you reefed on the brakes hard.