"Speed Wobble"

"Speed wobble" is a term I've heard thrown around alot in my life time so far. But really, what does it mean? In the sense I've heard it used over and over it would seem that if you take a 2-wheel vehicle above a certain speed it will wobble out of control and crash. I know that is not true at all, but many still speak of it.

It sounds ridiculous to me. Imagine a motorcycle manufacturer reporting the top speed of a particular bike. "Theoretical top speed, 220km/h, wobbles at 170km/h so you can't go faster than that."

I've heard it claimed on anything from bicycles, motorcycles, atv's and probably other stuff. I've taken a bicycle as fast as it could go down a steep hill in top gear where you can't possibly pedal faster because the tallest ratio is not enough. I've taken my motorcycle to 150km/h and never experienced this.

In my own experience its quite the opposite. The faster you go on a single track vehicle the more gyroscopic effect the wheels have and the more rigidly the vehicle stays up right. I feel this to be true on a bicycle or motorcycle. At high speeds it starts to take some effort to make a bike change course.

Then end of that rant, could somebody enlighten me as to what "speed wobble" means? Is it simply continuous overcorrection at high speed?

 

Here you go.

Google and Wikipedia are your friends.

 

Whoa! Thats a lot of info! But what does it all mean? It'll happen sometimes to some people on some bikes? And If it happens to me on mine I should relax my arms and slow down or speed up? Its never happened to me, but my dad always said crouch down to increase your wind resistance, and speed up. Anyone want to fill inthe gaps here for me?

 

It means that the Geometry of the front and rear wheel need to be perfect in order not to have either of the two wheels start "Hunting" for a straight line to follow.

The Front end, on a drive shaft bike, is usually the problem ... because the rear end doesn't get adjusted.

Rear-ends on Chain Drive bikes can be mis-adjusted a degree or two and throw-off the line.

Bearings, particularly the Head Set Bearings, might be too loose or too tight for the straight line vector to be steady. A "Hitch" in the bearings from being worn would tend to HOLD the steeering in a false line and the gyro forces would correct it. When this happens in high frequency, the front end wobbles ... looking to straighten itself from the false line the worn bearings hinder it from finding.

Loose bearings do the same thing. The smoothness in left to right and back transitions is not present and the front end seeks a random line to make the bike follow.

Fairings and windshields not completely aerodynamically tuned for the bike can cause the front end to drift as the Foil searches for a balanced "Slipstream" through the pressure of the oncoming air.

This problem is what causes the instability that destroys the handling characteristics at high speed.

The XJ900RK's Front Fairing (1983) was an aerodynamic problem. One which Yamaha corrected on 900's made after 1984.

 

I've never experienced it on a motorcycle, but speed wobbles on a skateboard are kind of like a warning that you're about to eat it and there's nothing you can do to stop it, haha.

 

What it means is relax your arms, slow down, lean forward (so as to lower the hight of your body and thus the centre of gravity) and hope.

If you have a fat gut you are more at risk (I'm skinny!), bike cops need to lay off the doughnuts!

Don't speed up (as you will have to go through the same speed on the way back down).
Don't fight it.
Reduce your speed.
Don't Panic!

 

I told of my horrifying eposode with highspeed wobble several months ago. Many things came to gether to make me say my prayers, very quickly, before I was able to get the bike back to an attutude it was compliant with. Here are the components of my problem; unbalanced (not badly) front tire, seperating threads only at high speed of the rear tire, worn headstock bearings, and a handle bar mounted fairing. Oh and a mechanic that was USELESS.

All these components working against each others forces caused a harmonic oscillation of the front and rear wheels, the fork and the frame.
This resulted in a mild wobble at 75mph. as I slowed it became worse(???) At 55 my bars went near bumpstop to bumpstop and left 9 45 degree angled rubber marks on the highway. At 45 a maricle interceded and the bike straightened out. I rode at 35 mph for 10 miles till I got home.

I have heard of noone else in 33 years of riding who can say they lived to tell this tale at this extreme. I am truely blessed.

It is REAL problem and expect it to happen to you some day especially if your playing with old bikes.

Just don't panic and grab a handfull of brakes.... that would kill.

 

Indeed.

If anyone needs confirmation that speed wobbles are real, grab a skateboard and go to your towns steepest hill. Ride down it, come back here and report your findings.

 

I can't get a skateboard that's rated for XXL. I'm way too large for even thinking about doing that. Large? Heck with large. How about -- too OLD; too!

Pushing 60. Nope. 60's pushing me! Next June I rack-up the Big Six-Oh and still ride every day it ain't raininng and am taking the bike out for a little cruise over to Dunkin Donuts right after Posting this afternoon's check on the site.

 

I had that happen a few times on my board as a kid and vowed to defeat it. The only way I could get through it was to dip into a steep turn the second it started to wobble, then zigzag like a skier to the bottom. Didn't always work, and would kill you on a bike, but was a handy thing to know about.

I've always been told to stiffen up your arms when you get a tank-slapper going and gently ease off the throttle. Never had the need to test that, and hope I don't. Here's to not taking unnecesary risks with the working condition of your bike.

 

The town I grew up in didn't have hills. But I can say from experience that 30+ mph hanging onto the tailgate of a friend's pickup in the school parking lot will teach you everything and more you need to learn about speed wobbles, hahaha.

 

All this talk about jelly frequencies is makin' me hungry...

My Little brother broke his collar bone racing a car down a hill at 40 Mph... on a skateboard.

I still call him a DA for it.

 

I've experienced speed wobble on a bicycle, going down hill... About the same time, my ass experienced pavement, and the bicycle experienced a gentle tumble about 30 feet down the road.

I guess that's why crotch rockets have steering dampers...

 

Thank you. The Wikipedia explanation was kind of heavy but the rest started to bring it together for me.

I have to wonder then, if a bike is in perfect mechanical order with wheels that will run dead true, and lets throw a steering damper in there, the condition should (in theory) never happen then? Of course there are always other variables.

On my xj one time I had to break quickly and momentarily from about 120km/h when a vehicle pulled out on the road. The bike dived forward and wobbled briefly which came under control in a second. It made my heart skip a beat though. I didn't know if that would elevate to an uncontrollable wobble or not.

The concept still scares me to try and run my bike too fast however. I don't want a spontaneous wobble because I pushed the bike to 170, that would be bad.

 

The Honda ST1300 has come under a lot of scrutiny in the last couple of years because of the death of a UK police officer due to a "speed weave".

http://news.bbc.co.uk/1/hi/england/mers ... 600897.stm

Apparently the weight of the police equipment shifts the weight bias enough to cause severe problems at high speed. One of the investigators looking into the problem was also thrown off of the bike, breaking several bones.

I think many (all?) of the UK police departments using the bike removed them from service. A tragic and expensive experience for the departments, and a PR nightmare for Honda.

It seems that a "speed wobble" or "head shake" can be cured with a steering damper, while a "speed weave" is a different and more dangerous phenomenon.

Herb

Did y'all see the video link at the bottom of the Wikipedia article linked above? The first actual occurrence of the death wobble I've ever seen. Scary...