Rear chatter?

[Nutter34]

Hey guys, I've recently bought an 89 ZXR400. It's running pretty worn GPR70's. I went to Ruapuna this past weekend and was suffering from chatter from the rear end, usually at max lean around the apex. It's worse the later I get on the gas but still there even if I do start the drive a bit earlier... I also noticed it more on the slower to medium speed corners...

Firstly, do you think new tyres will solve the problem or aggrevate it? I intend getting new ones anyway, just trying to plan ahead...
Secondly, what's the main possible cause? Too little/much preload, rebound etc?
Thirdly, does anyone know if there's a common shock repacement for the ZXR's, like a ZX6 or Gixxer 6 shock?

Thanks for any help.

Paul.

PS, it's only my second time out on the bike and was lapping around 1m52's, if it helps for information....

[James Deuce]

Raise your idle speed to about 2-3000rpm and see it that fixes it.

Add a couple of increments of rebound damping, or back compression off.

[idleidolidyll]

Hey guys, I've recently bought an 89 ZXR400. It's running pretty worn GPR70's. I went to Ruapuna this past weekend and was suffering from chatter from the rear end.

Firstly, do you think new tyres will solve the problem or aggrevate it? I intend getting new ones anyway, just trying to plan ahead...
Secondly, what's the main possible cause? Too little/much preload, rebound etc?
Thirdly, does anyone know if there's a common shock repacement for the ZXR's, like a ZX6 or Gixxer 6 shock?

Thanks for any help.

Paul.

PS, it's only my second time out on the bike and was lapping around 1m52's, if it helps for information....

Had the same question asked of me years ago when I loaned a guy my race bike. He was having serious 'chatter' issues under brakes so I told him to forget about the rear brake and just use the front.

worked a treat and he won every race smiling

yours might be the same but it could also be worn shocks, tyres, swingarm pivot, alignment etc

[Crasherfromwayback]

Also....and no, I'm not taking the piss...tyre pressure.
A tad too low, and you can induce a slight 'bounce'....

[avgas]

My old zxr (now KLOWNS) has a non standard 89 zxr shock, and rear swingarm. Ask him if he has actually found out what it is off yet....i suspected the zxr600.
Also watch out for the Kickback bullshit thing that the 89 zxr4 had, KBTTL or something - caused heaps of annoying chatter for me. found it was cos i was riding to low in the revs.....so that idle idea prob will fix u for the track.
BT's are the best rear for the zxr4 i found. fronts can be anything as it will chew them all soft in the corners anyhow - do you have adjustable forks? adjusting these can help your front tyre wear alot as the z's have a racy geometry.

[KLOWN]

i was told it was a standard shock by the guys who rebuilt it (the shock) but they weren't very sure.

[Nutter34]

Thanks for all the info guys.

Jim2, I only have 4 clicks of rebound, it's presently on 2, no compression I know of... I'll set it to 4 and see how it goes next time, though I'll probably have new tyres on, so it may be different anyway...

IdleI.... I'll keep that in mind. I use the rear sometimes, depending on the corner and approach. I'll have a good think about the corners and brake use, though this is usaully way after braking, close to the apex and driving out.

Crasher... Good point. I was running about 29 fr and 29 rr. Seems it's one of those feel things and personal preference things. Any suggestions from the other riders?

Avgas, this bike has been a race bike for years, but I'll look into this Kickback thing. The front tyre seems to be wearing quite normally. The rear is where I feel it and it's pretty well feathered. BT's... Those the Bridgestone 090's? The forks are standard 89 forks. They were rebuilt by a suspension guy in Chch. Adjustable for preload and rebound only. They seem to feel okay but one never knows how much one end affects the other...
As for the swingarm, the 89 had a braced swingarm, then from 90 on they had a different one...

Klown, thanks, so you're running a ZXR400 shock then... Hope for me yet then, lol...

Thanks again guys.

[Colapop]

So it's not the beans then...?

[MyGSXF]

suffering from rear chatter...

Hey P.. I would suggest turning off ya intercom set & telling the bitch on the back to shut da ferk up!!! :shutup:


lapping around 1m52's smarty pants... :nya:

[Nutter34]

Hey P.. I would suggest turning off ya intercom set & telling the bitch on the back to shut da ferk up!!! :shutup:

smarty pants... :nya:

I was wondering if you were going to show up... I only tell the wench on the back once, after that it's time for a spanking...

[MyGSXF]

I was wondering if you were going to show up...


ehh ehhh eehhhhh :shifty: you expect otherwise....:shit: silly boy.. :doh:



I only tell the wench on the back once, after that it's time for a spanking...

Well see.. that's exactly why I RIDE my own bike.. :yes: coz you boys is just tooooo bossy!!!!! :bleh:

[FROSTY]

Mate lets just clear this up.
were you on the FULL ruapuna track?
Were you having the problem everywhere or on specific corners?
Mate if it was full track then 1.52 is a pretty respectable time

[Crasherfromwayback]

Crasher... Good point. I was running about 29 fr and 29 rr. Seems it's one of those feel things and personal preference things. Any suggestions from the other riders?

,

Yeah I think you might wanna come up to around 30-32 PSI (Cold)

I had problems with the front of my RMZ at Wanganui last time I raced there, tried more rebound damp (helped), but 2 PSI in the front cured it.

It feels like 'chatter', but it's kinda a combination of suspension AND tyre pressure....it's a mild 'bounce'.....

I'd recommend this to anyone going racing....buy yourselves a genuine HRC race and setup manual for a Honda RS 250. I raced one for a while, and the manual is worth it's weight in gold. I mean.....HRC know a bit about their race bikes yeah? They desribe what you're feeling so well in the 'suspension trouble shooting' section , then tell you how to sort it, it's uncanny!

Really helped me alot......I used to simply get on anything and try and ride round whatever problems I was having with the bikes......doh!

[wari]

HAve ya tride cuttin' back 'onda prune con-sump-tion .. :spudwhat:

WErks a treet fur me .. lessa that morre'a this .. => :drinkup:

[Nutter34]

Thanks again guys.

Frosty, it was the full track. I was only experiencing it on a few corners, the first hairpin, the right hander before the lefts into the dipper and the dipper. Those corners seem to be a bit more bumpy than the others, which may be setting the chatter off. I'm just trying to see what the cure may be...

Crasher, I'll be getting new tyres so I'll try the higher pressures and maybe just wind the rear rebound to full and see what it does. After that, it'll be shock rebuild/replace time, will see.

But thanks again guys...

[FROSTY]

not being funny here mate but are ya sure you arent tossing the bike down one gear too many going in? you may have been locking up the rear end

[Nutter34]

I don't think so, The bike's not moving or hopping when on the brakes or when I turn in. I change down for the hairpin but for the other two I'm actually carrying a gear from the previous corner and sitting at around 8-9 k/rpm. I found the engine would be scraming too high if I did go down the extra gear, so compromised on the drive side of things... The way I see it, it's easier to increase corner speed that way and it gets rid of the need to change up then down again.... It could still be too hard on the brakes, which could be upsetting the suspension though...

Thanks though. I'll concentrate a bit more on exactly what I'm doing and see if by braking earlier and trying to drive through more changes the behavior...

[James Deuce]

Raising the idle speed fixed what you're talking about for me.

Re. the shock: Good old Kawasaki! Undersprung, too much compression damping, and never enough rebound damping, even on max. I think you could probably get a fully adjustable Hagon replacement for around $800, or alternatively contact Robert Taylor or Shaun Harris to see if they can do you a reconditioned Ohlins for around that price.

Shaun is on KB and his user name is: Shaun. Don't tease him, he's a Ginga AND he's short.

Robert Taylor can be contacted at Hawera Motorcycles.

[Shaun]

Not sure about common replacement of another model sorry.

But I do know that a major part of your problem will be the spring rate in your shock, the STD spring is seriously soft in those puppies, apart from the fact that the STD shock is not a brilliant piece of equipment.

My crude fix suggestion, find a way to increase the amount of preload that is on your spring currently and go and try again

[Macktheknife]

Go easy on the beans
Sorry couldn't resist.

[The Stranger]

Speak to ArcherWC, he had a lot of problems with rear chatter on the busa everytime he goes over 140kph after having installed an intercom system on the busa - Silly bastard.

[Nutter34]

Thanks Jim And Shaun. I'll try the idle trick. I've heard of it before but I'll definately try it now.
Shaun, what are good rider sags to have front and rear as a general rule? 25-30mm I guess? Also, would the front be inducing the chatter somehow, as in too little preload up front somehow transferring it to the rear?

Mack, I'll take the chatter from beans over suspension chatter anyday, lol...

Stranger, any chatter from the back gets a warning, if it's still there, a spanking is then in order...