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Discussion in 'Mechanical & Technical' started by jezterr, May 18, 2005.
can someone describe what chatter is like? ie from hard braking? just curious...
Chatter is scary as hell. It happens to me when I get hard on the throttle and the front end hits a bump, the bike starts to do a huge ass wable/head shake/chatter. If ya have a steering damper, that works pretty good at elimanting alot of chatter.
i thought chatter was different. what you described was a tank slapper. that's never good.
chatter is when your back tire is trying to get traction but is moving at a different speed than the bike itself. Usually seen under heavy braking when you take the weight off the rear and it starts to slide a little...then catch...then slide...then catch. It's never fun, and will cause you to stop in a greater distance than expected. Kinda similar to head shake, you'll know it when you get it. The ass end will bounce/shake until the tire speed matches your bike speed. At least that's how I define it.
so does chatter or headshake mean anything is mechanically wrong with the bike?
no...it's just one of those things that comes with hard riding. But both are (technically) caused by the rider. Point being that if you adjust the way you ride, you can limit the amount of both you get. You'll get headshake for turning your handlebars ever-so-slightly at high acceleration or if the front comes off the ground anywhere from 1 inch to 5 feet. Some bikes get it worse than others because of their steering geometry/angles, or because of tires. You can't really control chatter, but try experimenting with different riding techniques when you KNOW it's gonna chatter. Feather the clutch a little more upon downshifting. Try increasing your speed. Try decreasing your speed. It's one of those things that you have to figure out for your bike and your riding style. As long as you don't panic when it happens, you should be fine.
okay. what about headshake from hard braking?
reason for asking: jafar took my bike out yesterday and he said that under hard braking from freeway speeds, the front would shake. i've yet to duplicate this situation, so maybe it's all for naught... he's got me worried about my rotors and brakes.
I guess I shoulda said above that if you get chatter, you should adjust your suspension for the setting. It can be eliminated with adjustments. Try stiffining up the front forks. This may keep the ass end down a little more for breaking. As for wobble of the front under breaking would make me think you could have warped rotors or a bent wheel. You shouldn't really get head shake under deceleration (unless coming down from a wheelie).
I agree, sounds like the front rotors are warped. I'd start there cause its most likely. I know in cars if you get vibrations other than during braking it can be caused by such things as tires seperating, mis alignment and/or unbalanced/misbalanced tires. since i haven't really heard of bike tires separating and its mainly on braking, rotors seem like a logical (and probably cheaper) place to begin your troubleshooting.
that's what i was hoping it wouldn't be was the rotors... but because it's something i haven't noticed myself, i may hold off until i get the tires changed again... but something i'll definitely check before the seattle 100.
how easy is it to bang the rotors back into shape?
not, u could damage them even more?! But thats my experience. Someone might know a way that could work.
Well banging them may not be the best thing to do actually, don't bang them. I'm not entirely sure if its possible on bikes, but on cars you usually can have them "turned" which means they grind off a little bit (within factory specs). I've never had to do that on my bike so I'm not sure ( I STILL have the factory pads after 3 years). if its appropriate for bikes, it should be cheaper than buying new rotors. Usually you can only do it one time though. Good luck.
I turn rotors at one of my jobs. You cant turn a drilled rotor with out destroying it. You could check with your local bike shop, and ask them fro recomendations.
oh. i was just gonna take a hammer and bang away... damn.
i'll have to get the rotors checked, and if they are bad and grinding them isn't an option, then i'll have a reason to get some ebc rotors...
In light of the speeds, the feel, and the necessity of the front brakes to perform PERFECTLY, dont waste your time with turning the rotors. Your braking surfaces, no matter how competent or arrogant the tech may be, will never be as good as a new rotor. They are relatively inexpensive if you go aftermarket and standard drilled (wavy can get pricey but look pretty and stay fairly cool in comparison), but are well worth every penny to replace instead of ghetto up a set of turned ones. Dont sweat it until you can recreate the issue though.
On chatter, I get it on ocassion when trail braking and downshifting on the princess, the torque from the twins are notorious for making the ass end chatter. I couldnt dial it out of the suspension mainly because its a shifting and overrev issue for me, due to a lack of skill. Track days or practice is a good way to keep it from happening.
I know I'm late, but why bother fixing a problem that never happens for you? Your friend may have hit some bumps, he may be a good bit heavier than you and be overloading the suspension so that it takes away traction from the front tire, he may be overbraking. If you don't get chatter, or vibration (and warped rotors would mean that you, your friend, or Santa Claus would feel vibration when braking -all- the time), then roll with it.
If it is chatter, which as I know it is the tire grabbing, then slipping, then grabbing, then slipping, repeat ad nauseum, the likely culprit is tire, suspension, or chassis related stuff. Something that is using up so much traction you are going back and forth between grippin and slippin.
okay, well, after my weekend trip, i finally found what jafar was talking about. braking hard at anything higher than 70 mph, the front would vibrate as if the rotors are off. it's not as violent as jafar might've led me to believe and i've asked a lot of my other resources and it turns out that it's common on my bike... BUT i'm still going to clean off any brake deposits that could be doing this, and if that doesn't help it any, i'll be looking at getting new rotors. and if that doesn't do it either, then i'm out on a limb.
Holy cats! You guys need to read a few good books on motorcycle racing/performance handling before you go any farther with this discussion. Rear wheel hop is caused by hard braking that transfers weight to the front tire, decreasing the traction available at the rear. Front tire chatter is usually caused by the same heavy braking, but can also be a result of cornering hard. It is when the front tire alternately slips and regains traction and is a function of a lot of variables- tire design, tire temperature, fork and frame flex, tire compound and riding style. Kevin Cameron did a nice piece on chatter a few months ago in Cycle Guide, if my memory serves me. If your rotors were warped, you'd notice it first as a slight wobble during light braking and it would get worse up to a point as you braked harder, but would diminish as front tire friction with the pavement acted as a damper to the lateral movement.
How do I know these things? 30 years of wrenching and racing and instructing. Don't mean to be insulting to any of you, but just couldn't let you go down the garden path any further. If your front tire wobbles a bit under heavy braking from highway speeds, the first thing you should do is check your tire pressure. I'll bet its low.