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Almost died last night...

Old 05-25-2012, 05:45 PM
Thread Starter
Join Date: May 2012
Posts: 71
Default Almost died last night...

Caught the speed wobbles accelerating from 120 on a rough road. Never happened to me before, held it together but it made me think... Anyway, as well as attaining a steering dampener, is there a way to avoid these wiggles or to predict at what speed/rpm range they will most likely occur? I was led to understand that their occurrence has to do with the resonant frequency of the wheel matching that of the bike or something like that. On certain roads in california there is a regular <bumpbumpbumpbumpbump> that will become very uncomfortable almost immediately, especially after you reach a certain speed (I usually have to stand up a bit on my pegs to deal with it) but is it possible that this road surface created some kind of resonance in my bike/wheel/both that led to my handlebars oscillating? Again I was doing about 120 at about 7900 rpm on a road with a consistent and regular series of bumps... Stupid, I know. I had never accounted for steering wobbles previously as they had never occurred. From now on I will be more mindful of their likelihood.

Oh and one more thing: I usually aim to cruise at 7900 rpm because I begin to feel/hear this delightful whistle/hum at that precise rpm area. I generally try to upshift from that approximate range as well when I'm riding casually because it seems that the bike will effortlessly slip from one gear to the other without much change in actual speed, sort of a "sweet spot". It happens that it was at this rpm area that I experienced the wobbles.
Old 05-25-2012, 07:06 PM
Senior Member
Join Date: Nov 2011
Posts: 430

From what I understand the wobble occurs when you accelerate hard over rough/bumpy pavement so try to avoid doing that.
Old 05-25-2012, 08:31 PM
zaqwert6's Avatar
Nov 2011 ROTM
Join Date: May 2010
Location: O-Town
Posts: 655

Theres not a whole lot you can but , and I know this might sound weird, don't fight it. That usually makes it worse. Try and keep it straight and up right but do so with relaxed arms and passively.
Old 05-25-2012, 09:15 PM
Ghost1's Avatar
Join Date: May 2012
Location: Wahiawa, HI
Posts: 42

My bad for being "Captain Effin Obvious"... but, unless youre on a track, maybe just stick to the speed limit? Its just way too coincidental when people claim they've almost died, yet when they spread the details they include actions that kinda put themselves in the position....

Actually bro i already know i sound like the guy who at the moment offers "2 cents" that no one wants to hear, i just hate sitting by after hearing your story and not saying anything. Just be safe and smart.
Old 05-25-2012, 11:17 PM
tucsondude's Avatar
Senior Member
Join Date: Dec 2010
Location: Tucson, Az
Posts: 174

next time please dont specify you were doing 120 on the STREET, and put this in the how to: riding skills section...

at that speed it could be the wind buffeting...

check all your bearings and everything is nice and tight.
hows the condition of your front tire?
how old is your fork oil?

dont rely on the handle bars to maintain your position, or to control the bike. unless your going pretty extreme, bikes tend to right themselves
Old 05-26-2012, 12:27 AM
Wizzle's Avatar
Senior Member
Join Date: May 2012
Location: Northeast Tennessee
Posts: 140

Agrees with the last 3 posts!
Be safe.
If you're gonna go that fast at least be on a smooth straightaway or the interstate.
Or take it to the track.
But yeah, motorcycles will fix themselves if you let it. Just hold on loosely, but don't let goooo!
I swear that song is about a bike and not a chick..
Old 05-26-2012, 12:58 AM
Join Date: Aug 2011
Location: Toronto, ON
Posts: 58

It's happened to me once and it's definitely a little unnerving... though I was more shocked than anything at the time.

Like zaq said, don't find it. It'll usually right itself after a few seconds. And don't apply any brake as that's a recipe for disaster. Gently accelerating can bring you out of it assuming you're back onto smooth pavement but it's hard to control your throttle during a wobble, especially if it's a real tank slapper.
Old 05-26-2012, 01:34 AM
Shadow's Avatar
Redcoat, & Maxwell's Silver Hammer, MVN and curmudgeon
Join Date: Dec 2007
Location: Mud hut, Zululand
Posts: 11,614

Hard acceleration (and a lighter front end) will do that to you.................
Keep the front end down on rough surfaces.
Old 05-26-2012, 07:43 PM
Thread Starter
Join Date: May 2012
Posts: 71


I should go to the track if I want to go super fast, you're right. I know this. It's an impulse that I find hard to resist in the middle of the night in the empty, straight HOV lane of the freeway. Until I improve my skills I will resist the temptation to go so fast on public roads.

I also don't want to violate any forum restrictions by mentioning my illegal behavior. I don't condone or recommend it.

As far as the physics, well yes, I think the front end must have come up just high enough to be jogged to one side a bit by the rough surface of the road. I had the question about the matching resonant frequencies because of something I had read online about the subject, a phenomenon I still don't understand.

For instance I understand the physical nature of countersteering, which applies well to one of the points that was mentioned above about the bike "righting itself". The gyroscopic force of the spinning wheels make them want to stand on end, so that when you tilt them in one direction at high enough speeds, they will want to glide in the opposite direction to restore their perpendicular angle to the ground. (Simultaneously, pushing left makes your bike lean left as a result of inertia, which puts you and your bike at a good angle to the ground to corner sharply).

Basically, yes, I do stupid stuff like putting my life at risk for the sake of the thrill I experience when riding a motorcycle really fast and through twisting turns. I also enjoy rock climbing, a seemingly pointless activity to the objective. The result of climbing is that you go from being at the bottom of a rock to the top, almost always immediately before climbing back down again and carrying on with your life.

It's a somewhat mysterious part of my nature to me, but one that I have acknowledged and accepted. I have decided that to live without these experiences would be to live less fruitfully. I would like to live long as well as fast, and it's for this reason that I ask questions like, "what can I do to avoid this potentially fatal phenomenon whilst pursuing this incredibly entertaining venture that I've fallen in love with?"

If anyone knows the physics behind the seemingly arbitrary death wobble that occurs at certain resonant frequencies on a flat, smooth surface, please share your knowledge so that I and others may further understand what's going on.

Lastly, I would be remiss if I were to endanger or inconvenience my fellow man in the frivolous pursuit of kicks. I would not break the speed limit if I felt I was at any risk whatsoever of putting another person's wellbeing in danger.
Old 05-27-2012, 04:28 PM
Wizzle's Avatar
Senior Member
Join Date: May 2012
Location: Northeast Tennessee
Posts: 140

Eh, don't kick yourself too hard, we all do it sometimes!

As for the death wobble, it just means the front tire force has become
unbalanced with the road. (every action has an equal and opposite reaction)
Kinda like when you roll a coin it tries to stay upright But, at some point
it will start to wobble trying to maintain that centrifugal balance.

I guess that's a good way to explain it?
Somebody else might have an easier way to say it lol

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