The acoustics of speedwobbles

[SteveC]

I've heard that speedwobbles are caused by the vibation frequency of the two trucks coming into alignmant and feeding back on one another.

sort of like sticking a microphone up to it's speaker. Or a double wave out surfing...

While this makes sense to me, has anyone studied this?
do companies 'tune' their boards, or is it all trial and error...

Can any one shed some light?

[Crappysurfer]

the classic 'speedwobble' is from the rider, combination of quite a few things,
BUT
i think true speedwobble, like you are saying, happens often, but instead of being violent the truck just twitches in small amounts

[Skinart]

I've heard that speedwobbles are caused by the vibation frequency of the two trucks coming into alignmant and feeding back on one another.

sort of like sticking a microphone up to it's speaker. Or a double wave out surfing...

While this makes sense to me, has anyone studied this?
do companies 'tune' their boards, or is it all trial and error...

Can any one shed some light?

While this certainly seems plausible (We should send it in to Mythbusters!) I have some doubts
about it being an issue. If the conditions you are talking about are maintained, then the wobble
would become very violent. Resonant frequencys work.

However, I think it is very unlikely to be maintainable because you would need to maintain
a constant speed and/or road vibration. Or keep slipping into the right multiples of the offending frequency quickly
enough to maintain the resonance.

Even if this were to occur, it would be easily correctable by a weight shift, which would dampen
one of the trucks, or speed adjustment. Or at least, it should be possible, but then again, in spite of the
rather tricky nature of resonant frequencies, Galloping Gertie still happened.

[SteveC]

I've only really noticed it bad when a change of grade happens, or having one side in a seam.

as for rider, well that's where heaps of dampening happens, and I guess better riders can sponge up more vibration without transfering it back to the trucks...

I suppose you just do everything you can to minimise vibration without sacrificing much speed.

[Rabid Skunk]

I researched speedwobble a little a few months ago, and it is cause by resonance. When the vibrations are at your natural frequency when skating, you will get speedwobble. When motorcycle riders get to it, they have to stand off their seat because it gets transfered through the soft seat. So as long as you can stay rigid and absorb the vibrations, rather than being moved by them, you will be ok.

[shnate*]

speed woblles are cause by rII's and jimmy legs. harmonic resoncance probably matters at like 120kmh get some jimz's and some skill and you wont get speed wobbles

[SteveC]

EDIT<^^^Helpfull... but I absolutely agree about R2's sucking, damn thing wouldn't know square if it was melting them!
I havent had a speed wobble in years. without doing something stupid anyway...

As for 120k, well.. lets just say you've got a fastish road with a rough section, tripling vibration for say 30 meters before going smooth again... a very real scenario where I live... >

Perhaps it's about preventing vibration and then giving whats left no room to move.
Rather than stopping the trucks from 'talking' to one another,

So...
soft wheels would be good.
Soft bushings would be good..errr, no that can't be right can it?...
soft risers/mountings would be good.
a hard board would be good.
a solid but dynamic riding stance would be good.

I guess that the low truck angle also means that less vibration is turned into steering.

We do all this already.....Hmmm what else is there...

I'm just trying to think what could be done other than wheelbase/truck angle.
Shoes not too soft?

Geh... where's my engineering/physics degree when I need it?

[robotopdx]

if you can relax enough the wobbles will not get you. riders who are really loose can ride almost any truck - bushing combo without getting wobbles. so if they hit you just close your eyes and think about surfing clean waves on a warm day. it helps!

[Jam]

Yeah, from what I understand, speedwobbles are initiated by slight wobbles in one's body OR one's skateboard, and then the wobble is transfered and magnified when it is transfered to the other part (the rider to the board/the board to the rider....I don't know where it is started first...)

[SteveC]

See thats the thing, I've always believed and 'felt' that a relaxed stance helped dampen vibration or at least not transfer vibration from one truck to another.

It's one of those things where the fear of wobbles causes tension. which causes wobbles.
and the whole "never gets speed wobbles" thing is to help people trick themselves into thinking that they're safe from them...Or just to sell them

Of course you are safer from, on yes even R2's than say, Grind Kings. but I hear people say "never" way too often, It's a myth of skating, I hear tech skaters say it all the time "wow you've got those trucks that never get speed wobbles"... Grrr Lies...

[longboardorific]

most of the time speedwobbles are do to a rider gettign nervous and starting to shake with the adrenaline.when they start to shake it caues the trucks to wobble back in forth. then the truck loose contro and the rider goes flying. i think......

[Rabid Skunk]

When I was at a race, on RIIs, the first couple runs I could feel a little wobble, not much, but just the feeling of it. After a run or two, I got used to the speeds we were hitting, very fast, and didn't get any more wobbles at all.

[SteveC]

Ok, We all agree that the rider plays a huge part, but what else can be done?

there has to be something. Surely?

will a board on a dyno, with no rider, just a static weight, get wobbles?
guess you'd have to drag one down a runway or something to get the vibrations right...

Hell the rider could play 99% of the role. I don't know for sure.

[Rabid Skunk]

Ok, We all agree that the rider plays a huge part, but what else can be done?

there has to be something. Surely?

will a board on a dyno, with no rider, just a static weight, get wobbles?
guess you'd have to drag one down a runway or something to get the vibrations right...

Hell the rider could play 99% of the role. I don't know for sure.

What would put the weight on the board to turn it?

[SteveC]

well I dont know about turn but you could put weight on it easy enough

You could make it turn if you felt like putting a weighted robot on it, but who has the cash for that?

Turning would change the experiment anyway.

[funkyphreakout]

I've heard that speedwobbles are caused by the vibation frequency of the two trucks coming into alignmant and feeding back on one another.

sort of like sticking a microphone up to it's speaker. Or a double wave out surfing...

While this makes sense to me, has anyone studied this?
do companies 'tune' their boards, or is it all trial and error...

Can any one shed some light?

Yes, speed wobbles are caused by resonant frequencies, and yes, it is ALL your fault as the rider. The concept of resonant frequencies between two imprecisely manufactured skate trucks in a crude real world environment is completely preposterous. Set your board down at the top of a hill, and at the sacrifice of your deck, let 'er rip, no rider. It's not going to begin oscillating violently, or oscillating at all. If anything it'll veer one way or the other from naturally occurring misalignment.

However, resonant frequencies DO cause speed wobbles, just not what you're thinking. Try this passage from Wikipedia (regarding a phenomenon in flight) on for size:

"Pilot-induced oscillation (PIO), more correctly named pilot-aircraft-coupling, occurs when the pilot of an aircraft inadvertently commands an often increasing series of corrections in opposite directions, each an attempt to cover the aircraft's reaction to the previous input with an overcorrection in the opposite direction. As such it is a coupling of the frequency of the pilot's inputs and the aircraft's own frequency."

You get up to speed, and due to the fact that trucks don't have differential steering based upon your speed, any instability (loose trucks) that causes you to turn slightly is exacerbated by your subconcious that wants to go straight. You end up repeatedly over-correcting, and things get worse and worse until the bloody end.

And for those of you that think this explanation isn't the truth (or at least closest to) I point to "carving out" speed wobbles. Direct input to make a hard turn overrides your mind's unintentional "straight" thinking.

[Skinart]

"Pilot-induced oscillation (PIO), more correctly named pilot-aircraft-coupling, occurs when the pilot of an aircraft inadvertently commands an often increasing series of corrections in opposite directions, each an attempt to cover the aircraft's reaction to the previous input with an overcorrection in the opposite direction. As such it is a coupling of the frequency of the pilot's inputs and the aircraft's own frequency."

You get up to speed, and due to the fact that trucks don't have differential steering based upon your speed, any instability (loose trucks) that causes you to turn slightly is exacerbated by your subconcious that wants to go straight. You end up repeatedly over-correcting, and things get worse and worse until the bloody end.

And for those of you that think this explanation isn't the truth (or at least closest to) I point to "carving out" speed wobbles. Direct input to make a hard turn overrides your mind's unintentional "straight" thinking.

That's what I would expect. I know that this is what happens on a motorcyle. Otherwise you could just pull in the clutch and ride it out. I've had it hit me once and that was at under 20mph (on a motorcycle). I was taking a safety course, got confused for a moment in one of the excercises and it was all over.

[shapeshifter]

The acoustics of speedwobbles?

holy shiiiiiiiiiii...
eeeeeeeee...
iiiiiiiiiiiiiiiiiiiii...
eeeeeeeee...
iiiiiiiiiiiiii...
eeeee...
iiiiiiiiii...
eeee...
iiiiiiii...
eee...
tah!

[confusious]

Yes, speed wobbles are caused by resonant frequencies, and yes, it is ALL your fault as the rider. The concept of resonant frequencies between two imprecisely manufactured skate trucks in a crude real world environment is completely preposterous. Set your board down at the top of a hill, and at the sacrifice of your deck, let 'er rip, no rider. It's not going to begin oscillating violently, or oscillating at all. If anything it'll veer one way or the other from naturally occurring misalignment.

However, resonant frequencies DO cause speed wobbles, just not what you're thinking. Try this passage from Wikipedia (regarding a phenomenon in flight) on for size:

"Pilot-induced oscillation (PIO), more correctly named pilot-aircraft-coupling, occurs when the pilot of an aircraft inadvertently commands an often increasing series of corrections in opposite directions, each an attempt to cover the aircraft's reaction to the previous input with an overcorrection in the opposite direction. As such it is a coupling of the frequency of the pilot's inputs and the aircraft's own frequency."

You get up to speed, and due to the fact that trucks don't have differential steering based upon your speed, any instability (loose trucks) that causes you to turn slightly is exacerbated by your subconcious that wants to go straight. You end up repeatedly over-correcting, and things get worse and worse until the bloody end.

And for those of you that think this explanation isn't the truth (or at least closest to) I point to "carving out" speed wobbles. Direct input to make a hard turn overrides your mind's unintentional "straight" thinking.

about time someone got it right.......great explanation

[lettucefresh]

holy shiiiiiiiiiii...
eeeeeeeee...
iiiiiiiiiiiiiiiiiiiii...
eeeeeeeee...
iiiiiiiiiiiiii...
eeeee...
iiiiiiiiii...
eeee...
iiiiiiii...
eee...
tah!

about time someone got it right!!!



well, how about a piezoelectric dampening device that selectively identifies overcorrections in steering and not all board imputs?
When you're racing though, you really want the most direct response, because if the rider is on 100% of the time, there would be no need for a dampening device. But i guess some people could get into it, and i know recreational skaters would. Hell, you know Mark Grimace would buy 3 just because he can.