HELP - Solve my dilemma - SPEED WOBBLE

Same hill every time, different hills, road surfaces???  How close is the Tarmac in geometry to the other bikes?  Length of stem?  Different wheels or same?

Lots of vague info so can't really make any recommendations.

The reason I ask is because the Tarmac is designed as an aggressive road bike and in the 61 you have a 74 degree steering angle.  A lot of the American designed frames have aggressive steering geometires because of the types of racing we do predominately here (criterium and shorter circuit racing).  Those types of races emphasize handling and cornering ability over high speed stability.

Some other manufacturers are also known for that and high speed wobble has been reported on them.

But since it is happening to you on all different frames I am at a loss of where to start to diagnose something.  Each bike probably had different wheels/tires.  But that is a place I would start.  Look for either the wheel to be out of true side to side AND up and down.  Then check the tire to make sure it is fully seated on the bead all the way around.

try this...its basically going more aero but will put the weight back in your normal CG...obviously don't pedal...keep the pedals parallel to the ground (on a clock left pedal at 9 and the right at 3 o'clock)or reverse this...whatever feels more comfortable...slide back in the seat and put your knees close together...the sliding back should cause you to have to reach farther forward and put a slight upward bow in your back and pointing your head down...look up only enough to see where your going...yes this will make you go faster...but at the same time I think your putting way too much weight forward of the CG and thats whats causing your speed wobble...

I had the same problem when I first started and thats what fixed me...I run down one hill on crappy roads at 45 mph without even a hint of wobble...

 be sure to have the correct tire pressure...and check for any loose spokes also...you can always just sit up and go slower down the hill...

Have you checked that the headset is at the correct tension?

Is the front quick release tight enough?

When this happens, does clamping your knees onto the top tube alleviate the problem?

When I first got my TiCycles Softride, I had a problem TTing on it -- the front wheel would oscillate violently any time I got it over 32mph. Same wheel I'd used on my Barkley Softride, so I knew it wasn't that. And the bars would be steady. It's just the front wheel would shimmy a good 3" or more at the leading edge. I traded out the Trek carbon fork for a Kestrel, and the problem went away, never to return. So it could be that you're riding a fork that's just too soft. Usually not a problem with the current market, but you never know.

Any wobble is always caused by an imbalance.

Matt Cazalas
Technical Writer

Network Cables

I have a bike that does the same thing.  It really helps to lift your weight off the seat but grip the nose of the seat with your thighs.  You can press your knees into the top tube a bit too.

Another sure fire cure for wobble is to put on the brakes.  Be gentle though, when you are nervous about the wobble you can clamp down too hard and go over the handlebars.

I have heard a lot of theories about what causes wobble, forks, frames etc.  I don't really know what is right.  I think in my case that the wheels have a lot of lateral flex and that is a main component in the wobble dynamcs.  Getting some stiffer wheels would move the harmonic frequency higher and out of my speed league.  I haven't had the money to get some really stiff wheels to try the theory out. 

I have an idea for a really cool home science project to measure the resonant frequencies of various part of the bike.  I will do it when I have some free time.  It will make great geeky reading for all my super techno BT friends.  It involves rubber mallets, microphones, a computer and Matlab.  Way cool stuff you can do at home.

TW

This was my suggestion also.  When going downhill, I get up to speed and stop pedaling.  Get in a good tuck and clamp my top tube with my knees.  I don't know why, but the more aggresive stance (weight on the front tire) and knee clamp really seem to help.

Same here, no wobble on my Trek 1500SLR going as fast as 45MPH downhill.   However, I do think about the relative danger and potential bodily damage if something went wrong while going this fast.