# Frame Instability / Oscillation at high speed?



## mister_ed (Sep 16, 2005)

I recently purchased a Trek Madone 5.2 SL. It rides great in the Dallas area, where the roads are mostly flat, but I recently took it to the mountains and did some fast 40+ MPH descents. On several occasions, I experienced a substantial instability or oscillation while traveling at 40+ MPH. The oscillation was self-sustaining. Once it started shaking, I could not stop the bike from shaking until I slowed down to less than 30 MPH. I could not find anything loose or broken on the bike. Both wheels are true and are secure in the fork / frame. The oscillation frequency was about 2-3 Hz and the shaking was left-to-right (perpendicular to the direction of travel). The bike did not break into oscillations each time I exceeded 40 MPH. It seemed to be more susceptible in a cross wind. This was actually quite scary, as I thought it was going to cause me to loose control. I never experienced this with my Cannondale R900. I have been riding for 14 years and have never experienced such a phenomenon.

I would appreciate any input on how to prevent this. Could this be due to the carbon frame?


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## rriddle3 (Aug 5, 2004)

Sounds like another "shaky bike" situation. There have been several threads concerning this problem and no concensus on the cause, but there are a couple of possible controling actions, primarily putting a knee against the top tube. In your case I bet the main factor was the crosswind that you mentioned. BTW, where did you get the "2-3 Hz" figure from?


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## mister_ed (Sep 16, 2005)

2-3 Hz is an estimate of the frequency of the oscillation.


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## rickko (Aug 3, 2004)

Wow! Sorry to hear this.

I ride a 2300 but yet to surpass 39mph. I have not encountered this problem yet.

OTOH, I have another vintage road bike built in 1977 that has ALWAYS had that problem only it starts at 34 mph. 

Its scary as hell! The 1st time it happened it took all of my strength and courage to try and move my hands to the brake levers because it was ocsillating so violently. 

Now I know when it'll start so I am prepared before I hit 34mph.

I have tried varying my sitting position, forward, centered, and maximum rearward, doesn't make a difference.

I have checked the wheels, changed tires, tubes, checked the frame but nothing seems to be out of alignment. 

I thought it might be the road surface but I can do it anywhere, anytime if I hit 34+ mph.

The only thing I think that might contribute to the problem is the fact its stock handlebar width is 35cm c-to-c and thus doesn't afford nearly the control a 44cm bar would.

Here's my opinion after living with this problem for 28 years, *TAKE THE BIKE BACK* and exchange it for another one. The bike shouldn't do it. 

If you never find the problem it will ALWAYS do it! But, if you do...... let me know the cure!

Good luck!
..rickko..


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## zac (Aug 5, 2005)

mister_ed said:


> I recently purchased a Trek Madone 5.2 SL. It rides great in the Dallas area, where the roads are mostly flat, but I recently took it to the mountains and did some fast 40+ MPH descents. On several occasions, I experienced a substantial instability or oscillation while traveling at 40+ MPH. The oscillation was self-sustaining. Once it started shaking, I could not stop the bike from shaking until I slowed down to less than 30 MPH. I could not find anything loose or broken on the bike. Both wheels are true and are secure in the fork / frame. The oscillation frequency was about 2-3 Hz and the shaking was left-to-right (perpendicular to the direction of travel). The bike did not break into oscillations each time I exceeded 40 MPH. It seemed to be more susceptible in a cross wind. This was actually quite scary, as I thought it was going to cause me to loose control. I never experienced this with my Cannondale R900. I have been riding for 14 years and have never experienced such a phenomenon.
> 
> I would appreciate any input on how to prevent this. Could this be due to the carbon frame?



I have an '05 5.2SL and have not experienced that. Indeed on my sunday ride I hit 45.8 (and I was touching the brakes!) While I can never say I am comfortable at those speeds (>35 or so), it is not because of this bike. BTW it is pretty much a stock set up. 

A cross wind, a bit of buffering, who knows what set it off, but once it starts. I would think that if it were wheels it would be a higher frequency (but I am guessing). I suppose my first places to look would be headset, fork, rear stays, frame, wheels. Is your chain loose? Try removing two links and see. Anything with mass once it gets into harmonic vibration ("death wobble") are the likely sources.

I hope you get it figured out, if it persists, I wouldnt hesitate in bringing it back to your point of purchase.

Zac


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## bas (Jul 30, 2004)

mister_ed said:


> I recently purchased a Trek Madone 5.2 SL. It rides great in the Dallas area, where the roads are mostly flat, but I recently took it to the mountains and did some fast 40+ MPH descents. On several occasions, I experienced a substantial instability or oscillation while traveling at 40+ MPH. The oscillation was self-sustaining. Once it started shaking, I could not stop the bike from shaking until I slowed down to less than 30 MPH. I could not find anything loose or broken on the bike. Both wheels are true and are secure in the fork / frame. The oscillation frequency was about 2-3 Hz and the shaking was left-to-right (perpendicular to the direction of travel). The bike did not break into oscillations each time I exceeded 40 MPH. It seemed to be more susceptible in a cross wind. This was actually quite scary, as I thought it was going to cause me to loose control. I never experienced this with my Cannondale R900. I have been riding for 14 years and have never experienced such a phenomenon.
> 
> I would appreciate any input on how to prevent this. Could this be due to the carbon frame?



Do you have the harmonic buzzkill dampers in your handle bars?

Are those bladed spokes? I get pushed around on my 2005 madone 5.2 with bladed spokes on a crosswind.. but have yet to achieve such a speed.

Is your butt in the seat or are you lifting your butt?


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## mister_ed (Sep 16, 2005)

I dont have any dampers in the handle bars, (I actually have not heard of these, what are they?). I do have aero-bars, so I wonder if those contribute....

Yes, the spokes are blade type and the shaking happened while in the saddle. I took it to the shop and they adjusted the spokes, and checked the head-set, but now that I am back in Dallas, I wont have an opportunity to see if it still goes unstable.

thanks for the reply



bas said:


> Do you have the harmonic buzzkill dampers in your handle bars?
> 
> Are those bladed spokes? I get pushed around on my 2005 madone 5.2 with bladed spokes on a crosswind.. but have yet to achieve such a speed.
> 
> Is your butt in the seat or are you lifting your butt?


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## bas (Jul 30, 2004)

Bontrager BuzzKill Harmonic Dampers or something... supposed to take away the shock on the 
handle bar. 

Some people say they don't work, others say they do. I think quality and type of material
of the handlebars come into play for those.

Have you tried contacting Trek and asking them? 

Anyway to borrow your friends rims/tires next time out on a descent? Maybe chuck the aero bars too?..

It does sound pretty scary and annoying.




mister_ed said:


> I dont have any dampers in the handle bars, (I actually have not heard of these, what are they?). I do have aero-bars, so I wonder if those contribute....
> 
> Yes, the spokes are blade type and the shaking happened while in the saddle. I took it to the shop and they adjusted the spokes, and checked the head-set, but now that I am back in Dallas, I wont have an opportunity to see if it still goes unstable.
> 
> thanks for the reply


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## zac (Aug 5, 2005)

Do your aero bars have the forearm rests? If yes, take them off and see what happens.


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## bas (Jul 30, 2004)

zac said:


> Do your aero bars have the forearm rests? If yes, take them off and see what happens.


Hey Mister Ed, 

read here too:

http://www.bikeforums.net/showthread.php?t=54327&highlight=descending+wobble

http://www.bikeforums.net/archive/index.php/t-57253

Seems like all bikes will do it at some point.


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## bas (Jul 30, 2004)

mister_ed said:


> I would appreciate any input on how to prevent this. Could this be due to the carbon frame?


more in the general forum area:

http://forums.roadbikereview.com/showthread.php?t=40430


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## whitebassbenny (Jul 27, 2004)

i got a trek1500 and i hit 45 w/o any shaking but i am also 5'10" #145 so that have to b a big part of it


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