Front End Bounce

Hey, I wanted to get some input from you guys on your thoughts of what is happening in this video. At about 24 seconds you can see and hear some bounce while I was under heavy braking. Wasn't sure if this is related to fork compression or something else. I would not believe that it is due to road condition as its a track. Story was, these two in-front of me were going very slow in turns and yanking hard on the straights. We weren't allowed to pass while at lean for this session so I went into the turn hot and off-line (so as not to stuff them in the turn), anyway the shutter happened under braking and just was looking for some education as to if its technique or the bike or what.

Front End Bounce Under Braking - YouTube

it almost looked like you locked it up for a second....do you have abs?

yamihoe said:

it almost looked like you locked it up for a second....do you have abs?

Click to expand...

Nope no ABS, I suppose I can't say its not a lock up at all. I really don't have a good sense for what that feels like, but I assumed I'd be on the ground or it at least wouldn't have bounced like that. It was a while ago, so it was a little out of my head, I'm guessing if it was a quick lock up and I let off the brakes the oscillation would have been more of a side to side than up and down like I was assuming it was?

I've had the nose compressed and chatter just like that. I beleive it begins with imperfection in the road, once about two iterations in with the chatter its now at your wrists. YOU the operator perpetuate it with your hand into the lever as we are unable to apply even brake force while the bars rattle.

I've got R6 forks and was going down hill pretty hot in corner using allot of brake and it began that chatter. Letting off was the cure. Its only done it once and its never happened again. I was leaned over and braking.

I'm curious what others have to say but I suspect several things stack up to make it happen; Perhaps the pads are partly to blame, tire pressure, tire loading, fork setup, road imperfections, rider input??? :don'tknow:

EDIT: is it fair to say we've all had the rear chatter while braking?

I had it happen to me a few times on heavy braking last year shortly after getting new tires put on. Once it happened on regular braking but after going over some tar snakes. At the time I was worried about pads maybe, or my new tires being off (PR3s with the weird rain lines). I couldn't replicate it in a parking lot though, and I haven't had it happen again all year this season.

Odd.

Looks to me like you hit those black skid marks on the track (which are probably a little slick compared to clean pavement) and the front wheel was locking up intermittently. I haven't experienced that on my FZ6, but on my bicycle it happens all the time.

I have had this problem in several forms for 9 years/80K miles. My suggestion is to go very low with front tire pressure to get greater contact patch. Once you can consistently do stoppies without the pulse/hopping, slowly increase by 0.5 PSI at a time until it returns. Right now, with a Bridgestone BT-023 I am running 29 PSI cold/sea level and the problem is gone.

I went off on this subject about 3 months ago, read this post so I don't have to bore everyone else again!!

http://www.600riders.com/forum/fz6-technical/46100-what-brake-pads-do-you-use.html#post502270

Cali rider said:

I have had this problem in several forms for 9 years/80K miles. My suggestion is to go very low with front tire pressure to get greater contact patch. Once you can consistently do stoppies without the pulse/hopping, slowly increase by 0.5 PSI at a time until it returns. Right now, with a Bridgestone BT-023 I am running 29 PSI cold/sea level and the problem is gone.

I went off on this subject about 3 months ago, read this post so I don't have to bore everyone else again!!

http://www.600riders.com/forum/fz6-technical/46100-what-brake-pads-do-you-use.html#post502270

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That was an interesting read! http://www.600riders.com/forum/fz6-technical/46100-what-brake-pads-do-you-use.html#post502270

FinalImpact said:

I've had the nose compressed and chatter just like that. I believe it begins with imperfection in the road (I know I did NOT skid the tire) and after two iterations in with the chatter its now at your wrists. YOU the operator perpetuate it with your hand into the lever as we are unable to apply even brake force while the bars rattle.

I've got R6 forks and was going down hill pretty hot in corner using allot of brake and it began that chatter. Letting off was the cure. Its only done it once and its never happened again. I was leaned over and braking.

I'm curious what others have to say but I suspect several things stack up to make it happen; Perhaps the pads are partly to blame, tire pressure, tire loading, fork setup, road imperfections, rider input??? :don'tknow:

EDIT: is it fair to say we've all had the rear chatter while braking?

Click to expand...

We need to discuss other bikes as surely its not just an FZ thing and those of us with different pads, tires, tire pressures, FORKS, etc add a new spin that says its NOT isolated to the nose.

How many of you that have this chatter issue ALSO HAVE stock rear suspension?? Once the BIKE is in motion the bars are hammering on your wrists, your wrists & hands are no longer applying even braking force. Anyway - I have to wonder how much the rear of the bike impacts this. I've had it happen on dirt bikes lots too!

Have had that problem as well, seems like it is after the brakes have some heat in them and when braking at a lean. Don't recall it ever happening while straight up. I have associated it with cupped tires but that may not be the case. With dual compound tires you can get some uneven wear in the area where the two compounds meet. Cali Rider has done a ton of stuff chasing the problem.

Who all has recently bled the brakes?
R1, R6, GSXR, pop into any forum and its there. SADLY; NOT ONE of the threads I followed drew a clear conclusion!

My best guess is rebound rate vs tire pressure and the two combined get into a an oscillation. Added factors could be AIR in the brake line and the hoses stretching under pressure. How many here have SS lines? Now add in rider jolting the lever and whalla! Also I didn't mention mine occurred going down hill at speed of 45+ mph.


EDIT:
(( PASTE FROM ANOTHER FORUM)) Others have thrown all kinds of time and money and HAVE NO CHANGE. A member called racetech. Read on. . .

I talked to the tech guys over at Racetech (951-279-6655) and they said this is a fairly common occurrence, the guy couldn't explain what causes it, which kinda bothered me. But he strongly recommended that I replace the springs with one that matches my weight. Also freshening up the internals and fresh fluid. So that is what I'm going to do.

It seems that the problem is not brake related at all, even though it only happens on the brakes, strange.

END PASTE::::>>>
All, do not walk away from this thinking spring replacement will fix your issue. It is PART of the equation but not the whole thing. It has to do with damping rates, tire loading, friction etc. IMO its very likely what I said up there. Damping rates (both compression and rebound) combined with tire loading and even the rear suspension setup.

I do not see value in replacing rotors unless warped or have hot spots, wheel bearings, or head bearings unless they FAIL manufactures specs. Its just a waste of money.