Rear Chatter

[Syx]

Not been around for a few months due to personal reasons, but I've had a trawl through and couldn't find anything on this.

I did a trackday a Mallory a couple of weeks ago, and bit the bullet and joined the advanced group. Thankfully not at the back, but with the ability to ride harder without the "traffic" I'm noticing that under hard braking I'm getting a fair bit of rear chatter on corner approach.

I'm thinking that this is one of a few things:
1) Too much rear brake
2) Too heavy with the clutch out after downshift
3) Incorrect suspension settings

I'm ruling out (1) because I can't see how I can be any lighter on the rear brake, I'm barely touching the thing.
For (2), I'm not blipping on the downshift (something I'm working on!) but am feeding the clutch in relatively softly and am still getting the chatter.
My feeling is that it's a combination of poor suspension setup (as the bike was originally set for someone heavier than I, and I've not changed it since) and still being too heavy on the clutch-out.

If anyone's got any input on a possible cause then feel free to shout! I was hoping that I might also get a few pointers into suspension issues to look out for; before the next TD I plan on getting it set up correctly for preload at the least so I can tweak accordingly when I'm at the track, but for all the suspension guides I've read none really deal with the issue of chatter as such - my impression is that it's likely due to be a combination of not enough compression damping at the front and too much at the rear.

Any comments are much appreciated.

[chris-red]

Not really a track boff, but I don't really use the rear brake unless in a bend,in traffic or in the wet. I rely on engine braking to slow the rear down.
____________________
Well, you know what they say. If you want to save the world, you have to push a few old ladies down the stairs.
Skudd:- Perhaps she just thinks you are a window licker and is being nice just in case she becomes another Jill Dando.
WANTED:- Fujinon (Fuji) M42 (Screw on) lenses, let me know if you have anything.

[Wafer_Thin_Ham]

I was under the impression the top boys simply open the throttle to help get rid of/minimize it. So whilst braking, open the throttle to take the slack out of the chain.

Or take it to some suspension chaps at the track and get it set up properly. It's not that much and certainly worth doing. Still on standard suspension?
____________________
My Flickr

[Phoenix]

If you're locking the back brake up then it will clatter, they do that, and it's very easy to do on track. It's probably not great but I purposefully bleed my back brake quite a little badly so that it's not as easy to lock up but still works perfectly well.

Practice blipping on downshifts on the road, makes your changes smoother and much less likely to lock up or make the rear skid a bit which is exactly the same effect as too much back brake. The quicker you downshift the less 'blip' you need as your revs don't fall right off so take too long over it and you're more likely to end up with a jolt as you have to guess what the engine speed is going to be based on your actual speed and the gear you've gone into, longer you take about it the more likely your guess will be off, meaning jolt or too high revs and clutch slip needed.

[jay81]

i would say it is nothing to do with your suspension set up, i had mine set up by 100% suspension last time i was at mallory and i still got chatter going in to the hairpin,
think it is just coursed by your rear wheel speed is slowing down to fast, so try not to go down the gearbox so fast, the way i get round it (when it happens)is to feed the clutch in or out untill the speed matches up and the chatter stops.
____________________
I had the cab driver drive me here backwards, he owes me ?27.50.
KTM 625 SMC

[Syx]

Thanks guys. I'm still on stock suspension; and I've not noticed the problem before advanced at Mallory.
Next track day will be Cadwell I hope, so I'll recheck the basics like preload/sag etc and see what feedback I get at a different track.

In any case, it looks like I'll have to be making a few adjustments to my riding style to eliminate it fully!