Just did half of a track day on my new bike its an 06 R6 with 25mil ohlins internals...anyway on the long sweepers i.e. T1 at jennings I was getting a chatter? Could this be due to too much grip...I mean too low PSI in the front? I was running Dunlop 211's and believe I was running the front 31.5 Hot. Thats what my guess is due to some imput by a "fast" guy Just wanted to get a few more opinions!
Hard to just say "do this" or "tweak that knob" and be correct. F/R weight bias, rear comp/rebound settings, wrong rear spring (adjusted to compensate to get sag "right") can foul up the front. The front has some effect on the rear but the rear can really mess up the front if the shock is "bound up" with too much damping or if it packs down. As you stated, front tire choice and pressure can also cause problems. If you have all the basics covered then those "simple" things can be crossed off the list, but if not...?
arn't you like 200lb +? not that thats a bad thing, just if that little bike is not sprung properly and the 25mm valved right you could get grip chatter. It is unlikely that a psi change will solve what you have. FWIW , try stuff. Add and remove preload, add and take away compression and rebound to see if it gets better or worse. Can pull in on pit road, make a change and go right back out. wait.. it is coming to me... i see THermosman or John with CTR in your future..
i would try slowing down the rebound a bit first (in the front), assuming spring rates are proper and sags have been worked out etc... dunlop recommends 31 cold and 33 off the warmers for the 211's, but for certain tracks they recommend 28 cold, so you're at least in the ballpark- i would look to suspension- not the tire.
UGA dawg, I have an 06' 636 w/ 20mm internals. I was gettin same chatter/packing, could not quite tell which, only in turns 13 and 1. Same 4 u? When I first got forks done it in 06' it was horrible, front end would bounce/chatter, so I took out some fork oil....it helped. Front end could be packin, which is not good, maybe too stiff on rebound not allowing fork to rebound over bump, that can cause crash.....crash bad. Also check fork travel w/ ziptie...10mm from bottom is good. As mentioned in other responses try adjustments and take notes....leave a screwdriver on pit out wall for easy access....just tell cornerworkers. hope this helps...i know i have same problem....went to jgp last weekend but rained afternoon so no time for experimentation...
If you are going to try turning knobs, back off on rebound and comp at BOTH ends to "free up" the chasis and see if that helps at all. Most guys bind up the chasis with excess damping until it gives a "safe" feeling or a more stable platform, but remember that max traction at the contact patch occurs when the chasis is just a tad unstable, or "loose". You don't want to trap energy inputs in the tire sidewall as the suspension has to be able to move with little delay to high (bump, not wheel) speed inputs. If you only get the chatter after you've been the sweeper for a "long time", I would back off the rebound front AND rear or perhaps go to a thinner oil (pain in the ass, I know) or (even bigger pain in the ass) change the rebound stack in the forks to allow for LESS high speed rebound. FWIW, the rebound knobs controll LOW speed rebound primarily and while they do have a minor effect on high speed oil flow in the forks, you can not adjust enough out of the low speed circut to make the high speed circut work right if the stack is wrong for your track/s. Lastly (not that you don't know, but just in case) low speed movements are the ones you can feel when you transistion side to side or bouncing on the bike in the pits, high speed refers to wheel movement over bumps that can't be felt as individual events. Lecture off...:up:
but... less rebound (softer) could allow the front to not pack up which could be causing the chatter. So, who knows.
I will be back at JGP the first weekend of Feb so I will try to tweak it a bit! After that, I am planning to really get it optimized for me and the new Michelins! Thanks for the help guys!
