CVCCA - Parker's Team

 I'm not sure which category this topic fits into so I won't be offended if this gets moved.

The other day I was coming down the 4 lane when I experienced my first case of bike wobble.  I was in the drops in an aero position when it began.  I'm not sure what speed I was going as the computer was not functioning.  I came out of the aero position and pressed my knee against the top tube.  I also tapped the brakes a couple of times.  The wobble let up and I was able to come to a complete stop.  I inspected the bike and everything seemed to be in working order.  I made it down without any further episodes.

 From what I read, this is some sort of physics anomaly involving foreign terms like nutation, gimbal and latent resonance frequeny.  I have no idea what any of that means.  Craig Calfee posted something about having an assymetric fork as a cause for wobble, while others have suggested loosening ones grip on the handlebars, changing the wheel, head set etc. 

My questions to the coaches:

a) Did I do something to cause this?

b) What is the best way to come out of it?

c)  Are there any mechanical issues I need to be concerned with? 

d) What is the best soap to clean my soiled shorts? 

Thanks in advance for the advice. 

Chris -

 I forwarded this one to my favorite materials engineer down in Irvine.   RE: part "D", well now that is a mom question and the answer is

throw Oxy-Clean in with your regular detergent.  (Hahaha)  Glad  you are safe.

Katie

Hi Chris, the "high speed wobble" you had could come from a variety of causes. The first thing to check is a loose head set or bad hs bearings. The front wheel might not be true which isn't noticed at slower speeds. Also it could come from either the position when decending or how tight you are holding on . Sometimes, coming down the four lane, you can pick up a side wind which could contribute...Or, it could have been just one of those things.

bob

You did the right thing clamping your knees on the top tube.  IT will scare the salt (or whatever) out of you though.

Once you have checked ALL the possible mechanical causes and find none, then it can be riding position, with a littel too much weight on the front end, OR  harmonics due to design and materials . 

Harmonic issues are  not going easily resolved... a stiffer fork might do the job,   or take my solution..buy an new bike.  My 'shaker' was my first Orbea, great ride, but with my position and WEIGHT it would go into harmonics at 38 or 39, and not go away until I was under 35.  I had a lot of coaches ride the bike (all lighter than me) and they had no issue... 

keep us posted I am curious now.  If you don't get it done before this weekend, have either Bob or I check your head set. 

 c ya

Hey Chris I have had this happen a couple times climbing the 4 lanes never coming dwn.

Scott

Chris -

First let me apologize because obviously I am not a coach... nor is your fellow anteater... that having been said, he tends to know about these things and here is his short version - Katie

Here is a link explaining speed wobble:
http://www.sheldonbrown.com/brandt/shimmy.html

In short speed wobble is an oscillation within the frame, think of letting a pendulum go and watching the ball swing back and forth.  In cycling, the bike acts like a spring while the rider is the mass.

Remember this is shortened-


Causes (things that can change the frequency of vibrations in the frame) :
1) Frame itself
    a) Frame stiffness (ties in with #3)
    b) Geometry (and how your body type fits on it)
2) Rider
    a) Gripping the bars tight
    b) Not holding on to the bars while descending
          i) This includes shifting from drops to hoods!
    c) Breaking, tapping breaks
3) Road quality- it all has to do with something to hit that "sweet spot" in


Solution:
If you experience speed wobble the first thing to remember is to relax.  These words are by far the most important, and most simple, ones in cycling and can be applied to almost any situation.

1) Loosen grip while descending.  A death grip will actually worsen the wobble
2) Don't be afraid to stand up to allow the bike to settle.  This is effectively removing the mass from the spring
3) Pedal! This offsets the oscillations
4) Hit some bad road.  Although a tiny bump may have caused the speed wobble, a good patch of bad road can offset the wobble (not for the faint hearted...be prepared!)

(*) The ultimate fix is to get a bike that fits your body type well and is stiff but realistically this isn't always an option and you may not know if the bike is uniquely perfect until you have it on the open road.  With that said though, you could get a speed wobble on virtually any bike with the right conditions.  It is all about eliminating the chances with the right technique and/or bike and reacting properly to the wobbles.

John Wolzmuth

a good patch of bad road can offset the wobble

See - those Madera roads are actually a good thing! :)

Thank you all for the great suggestions.  It may have been just one of those things as I have never had this happen before but I will definitely take my bike in to get checked out.  Katie, please be sure to tell John thanks for his input.  It must make you proud to have such a smart (and fast) kid! The oxy worked wonders by the way.  I'm on call this week but hoopefully I will see you all on Saturday.  In either case, I'll keep you posted on the wobble.  Thanks again.

Chris