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56mph scary death wobble.

golgiaparatus

Out of my element
Aug 30, 2002
7,340
41
Deep in the Jungles of Oklahoma
Wow, so on last nights ride I was in a small group on a long descent. We hit 56mph. Felt smooth and chill... but then all of a sudden I got a tiny wobble in the bars, which over the course of 2-3 seconds turned into a scary back and forth vibration. I slowly got on the rear brake and brought the speed down to about 35 and the wobble stopped. For a second though I though my wheel had come loose or something, it was scary thinking about hitting the deck at highway speed.

THis was the second time last night I felt it, the time before I was hitting about 40 but it wasn't a perfectly smooth road so I thought it was the surface. The time mentioned above was a perfect road... smooth as hell.

Has anyone experienced this? What is the cause and how can I rid myself of this problem... Honestly I don't think I'll be able to let myself get over 35-40 mph on my bike unless I know this problem has been eliminated.
 

SuspectDevice

Turbo Monkey
Aug 23, 2002
4,155
355
Roanoke, VA
There are a quite a few things that can cause DEATH WOBBLE. One thing you should know. Next time it wobbles stick a knee onto the toptube. It will help to dampen the vibration and should help to bring the bike back under control(at least a little bit).

1. The your wheels might be out of balance.
2. The geometry of the bike might suck.
3. The bike might not be straight.
4. Your position might suck.

I bet it's a perfect storm of all that stuff.
Post some pictures and measurements and a link to the geometry and I will try to fix it for you.
 
Mar 1, 2010
5
0
Dayton, OH
Speed Wobble (or "Death Wobble") is much less common now than, say, thirty years ago, because frame geometries are more standardized and workmanship overall is better. Assuming geometry isn't the problem, there's about a dozen other things, and I agree with Mickey that it's mostly likely a combination of some of them.

Jobst Brandt (the guy who literally wrote the book on bicycle wheels) says, Shimmy is caused by the gyroscopic force of the front wheel whose tilt is roughly at right angles to the steering axis, making the wheel steer to the left when it leans to the left. This steering action twists the toptube and downtube, storing energy that both limits travel and causes a return swing. Trail (caster) of the fork acts on the wheel to limit these excursions and return them toward center.

Two more very smart people, David Gordon & Jim Papadopoulos in their MIT-published book Bicycling Science, completely disagree. Since shimmy frequency is independent of bike speed, gyroscopic effects "are clearly not essential to the phenomenon."[2] The top five influences on wobble have been found to be lateral stiffness of the front tire, steering damper, height of bike center of mass, distance of bike center of mass from rear wheel, and cornering stiffness of the front tire.[3]

So where does that leave us regular folks? Simple: try changing the things you can, especially your position on the bike. Also check your wheels, headset, fork welds or bonds-- including fork ends-- and how your wheels sit in the frame.

If all else fails, I refer you to the great Eddy Merckx (really!), who said in response to the same question, Simple. Sell the bike and buy another.

Hope this helps.
 

golgiaparatus

Out of my element
Aug 30, 2002
7,340
41
Deep in the Jungles of Oklahoma
There are a quite a few things that can cause DEATH WOBBLE. One thing you should know. Next time it wobbles stick a knee onto the toptube. It will help to dampen the vibration and should help to bring the bike back under control(at least a little bit).

1. The your wheels might be out of balance.
2. The geometry of the bike might suck.
3. The bike might not be straight.
4. Your position might suck.

I bet it's a perfect storm of all that stuff.
Post some pictures and measurements and a link to the geometry and I will try to fix it for you.
This is the bike:
http://www.quintanarootri.com/G&C/split/split_spec.html
There's a geometry pop up near the lower left of the photo.
It's a 58cm with a 90mm stem. I run the stem about 1 spacer lower than is in the photo.
 
Last edited:

Bicyclist

Turbo Monkey
Apr 4, 2004
10,152
2
SB
Via Velonews

Shimmy is eliminated by increasing the resonant frequency of the bike,which means making it stiffer. Bikes that shimmy badly tend to be onesthat are very flexy, so it takes a long time to make a single back-forthoscillation.

It is especially common with tall bikes, particularly ones with small-diametertubes. All of that open space in the frame allows it to flex back and fortheasily.

A tall bike can be built not to shimmy by using a stiffer top tube –this may be the single most important frame member to stop the shakingback and forth. Larger-diameter tubes using a lowered or sloped top tube(or both) will help. So will a shallower head angle, and/or more fork raketo absorb more vibration in the fork.

More minor things also contribute, like pitted headsets, untrue wheels,wobbly tires and out-of-balance wheels. If you crank your rear wheel upto high speed on a work stand, the whole stand will jump up and down becausethe wheel is out of balance. When you let a wheel spin down without resistance,it will usually stop with the valve at the top, since the rim seam is heavier.

Using a tube with a longer valve, and/or screwing on valve collars untilit stops randomly will help balance the wheel, similar to how tire storesdo it for your car (and you know how shaky a car with unbalanced wheels can be).
 

Westy

the teste
Nov 22, 2002
54,225
20,003
Sleazattle
My bike gets the wobbles at high speeds if I stand up or loosely sit on the saddle. If I put the groinal death grip on the seat, wobbles go away. You and the bike are a system, yes a stiffer frame can help but if you stiffen the system it might work just as well.
 
This is the bike:
http://www.quintanarootri.com/G&C/split/split_spec.html
There's a geometry pop up near the lower left of the photo.
It's a 58cm with a 90mm stem. I run the stem about 1 spacer lower than is in the photo.
90cm on a 58cm? Do you have T-Rex arms? If not, get something longer...being that far back over the front wheel is gonna screw with descending like whoa. In the mean time, lowering the stem might help to put you further over the front wheel.

Also, don't descend like a mountain biker. Get your weight over the front wheel. Can't tell you how many Freds I've seen eat sh!t at 25mph with the death wobble because they're hanging their ass off the saddle with a mile of spacers under their 10 degree rise 80mm stem.
 

SuspectDevice

Turbo Monkey
Aug 23, 2002
4,155
355
Roanoke, VA
90cm on a 58cm? Do you have T-Rex arms? If not, get something longer...being that far back over the front wheel is gonna screw with descending like whoa. In the mean time, lowering the stem might help to put you further over the front wheel.

Also, don't descend like a mountain biker. Get your weight over the front wheel. Can't tell you how many Freds I've seen eat sh!t at 25mph with the death wobble because they're hanging their ass off the saddle with a mile of spacers under their 10 degree rise 80mm stem.
What he said.
I assume you got the Alex wheels. Pull those things off and mess with them. They might be a little too "factory fresh".
 

johnnypop

Chimp
Aug 24, 2006
86
0
San Jose/Santa Barbara
I've had that happen on multiple bikes (bmx, road, etc...). The road bike I traced it back to the front wheel that had some goofy balance issues. Pushing 40mph it would wobble bad and get worse with braking, scary to get it down to speed trucking into turns.
 

James

Carbon Porn Star
Sep 11, 2001
3,559
0
Danbury, CT
Speed Wobble (or "Death Wobble") is much less common now than, say, thirty years ago, because frame geometries are more standardized and workmanship overall is better. Assuming geometry isn't the problem, there's about a dozen other things, and I agree with Mickey that it's mostly likely a combination of some of them.

Jobst Brandt (the guy who literally wrote the book on bicycle wheels) says, Shimmy is caused by the gyroscopic force of the front wheel whose tilt is roughly at right angles to the steering axis, making the wheel steer to the left when it leans to the left. This steering action twists the toptube and downtube, storing energy that both limits travel and causes a return swing. Trail (caster) of the fork acts on the wheel to limit these excursions and return them toward center.

Two more very smart people, David Gordon & Jim Papadopoulos in their MIT-published book Bicycling Science, completely disagree. Since shimmy frequency is independent of bike speed, gyroscopic effects "are clearly not essential to the phenomenon."[2] The top five influences on wobble have been found to be lateral stiffness of the front tire, steering damper, height of bike center of mass, distance of bike center of mass from rear wheel, and cornering stiffness of the front tire.[3]

So where does that leave us regular folks? Simple: try changing the things you can, especially your position on the bike. Also check your wheels, headset, fork welds or bonds-- including fork ends-- and how your wheels sit in the frame.

If all else fails, I refer you to the great Eddy Merckx (really!), who said in response to the same question, Simple. Sell the bike and buy another.

Hope this helps.
That you Rick?
 

4xBoy

Turbo Monkey
Jun 20, 2006
7,014
2,847
Minneapolis
Maybe it isn't the bike, maybe it's just the oscillation of your jelly rolls causing excess turbulence at speed.
 

golgiaparatus

Out of my element
Aug 30, 2002
7,340
41
Deep in the Jungles of Oklahoma
90cm on a 58cm? Do you have T-Rex arms? If not, get something longer...being that far back over the front wheel is gonna screw with descending like whoa. In the mean time, lowering the stem might help to put you further over the front wheel.

Also, don't descend like a mountain biker. Get your weight over the front wheel. Can't tell you how many Freds I've seen eat sh!t at 25mph with the death wobble because they're hanging their ass off the saddle with a mile of spacers under their 10 degree rise 80mm stem.
I actually have a 110 sitting in my garage... I'll fit that and see if it helps out. Thanks...

And to suspectdevice: Yeah they are Alex Aclass wheels... Factory freshness is an understatement... after the first ride on them they both needed work. The are perfect in the stand now though.

Off topic... wednesday when I had the 56mph death wobbles I saw a whole team stopped on the side of the road. Turns out they they had a rider go down at around 50mph on the same hill... he's pretty torn up.
 
Last edited:

4xBoy

Turbo Monkey
Jun 20, 2006
7,014
2,847
Minneapolis
As a rule. Mine stopped after re-lacing the back wheel, so I guessed it was dish affecting front/rear wheel centering.

I had previously done other things to no effect - beefed up welds on swingarm, fabricated beryllium copper swingarm bushings...

You probably removed the exhaust spooge that was causing traction and balance issues. ;)


The H1 is a cool bike imho, but then again, any street legal two stroke is.