Severe "chattering" under hard braking?

EXTremist · 07-30-2007, 11:59 AM

Hi Guys,

I posted this in racer's area too but thought you guys might be able to shed some light on this phenomonon I experienced this weekend.

I had the opportunity to put about 15 laps on at a local 1/2 mile oval this weekend as part of a charity ride. I rode the track mostly in 3rd gear going down to second occassionaly when I needed to slow down for traffic.

The corners were high banked but the apex's fairly flat. I ride a stock 2007 R6s.

Several times under hard braking (from ~70 MPH down to ~40 MPH) I would get the sensation and noise that the bike was severely chattering (felt almost like the fornt end was bouncing slightly) it was scary and dangerous feeling. I would let off the brakes slightly and pull in the clutch to get it to stop. Once or twice I slightly skidded the back tire. I just don't know what to make of this...the bars felt tlike they were jumping a bit in my hands and it seemed like it would escalate until I let off and pulled in the clutch.

What was I doing wrong, or what could this have been? Any ideas?

Thanks!

bush · 07-30-2007, 12:05 PM

Were you locking the front tire?

cory1848 · 07-30-2007, 12:11 PM

I get brake chatter too, Some people say its warped rotors but mine are in spec, I have just learned to deal with it...

sqchram · 07-30-2007, 12:39 PM

Its your rear brake combined with the engine compression skipping your rear tire. As you apply more front brake the rear gets light and you will need to let off on the rear brake.

Anyway - thats what it sounds like. Be more specific. Front or rear?

MINI NSX · 07-30-2007, 03:00 PM

I always thought front-end chatter was caused from the suspension being bottomed out, like under braking, then the front tire bounces up and down, 'cause the suspension can't since it's at it's limit. Something has to absorb the bumps from the pavement, and when the suspension can't then the tire will.

You also mentioned that the track had banking, which will further compress your suspension.

EXTremist · 07-30-2007, 03:24 PM

Thanks guys - it's hard to say it felt like the whole damn bike was bouncing slightly underneath me. I think I can reproduce it braking in a straight line if I'm on them hard enough.

Will increaseing preload or compression damping help? Not that I'm coming to stops this hard a lot, but in a real panic stop this could send me flying or at the very least I'd have to let up.

I think I'll try to see if i can make it happen with very little to no rear brake pressure to try to narrow it to the front end. everything everyone said makes sense including the front-end being out of travel...is this where "works forks" would make the difference?

Hard to believe the rotors are warped...but then that's what the Jeep dealership tried to tell me for years too

bluespecv03 · 07-30-2007, 10:52 PM

Quote:

Originally Posted by sqchram

Its your rear brake combined with the engine compression skipping your rear tire. As you apply more front brake the rear gets light and you will need to let off on the rear brake.

Anyway - thats what it sounds like. Be more specific. Front or rear?

I agree. Ive had this happen to me numerous times, and it sounds just like youve described.