Psycho bike  

[Guest]

If I ride at around 35kph+ with no hands on the bars, my bars shake really bad. Does anyone know what could be causing this?

The bike is a cannondale with carbon folks.....

 

[Vo2]

• The rim could be out of true. Turn your bike upside down, spin the wheel and see if it wobbles.
• or, could be a bad tube. Sometimes tubes get bubbles.
• or, could be a bent axle

 

[Guest]

If none of the above seem out of order, make sure the headset isn't loose. Shouldn't be too tight either.

Or perhaps the bearing surface is badly pitted... hopefully not though.

 

[Guest]

Hi. This topic came up some months ago on one of the U.S. bike lists, and the responses were very good. One chap had his family filming from the back of their vehicle in front of him when his bike went into its violent wobble. At speed.

This phenonemon used to be known in motorcycle circles as  'tank slappers', for the handlebars would often be banging on the petrol tank. They were also often terminal. One way to get out of it, perhaps the only survival method, was to push forward on the bars, if poss., and accelerate. Bit hard on a bicycle, but you can lean forward and start pedalling again.
This has the effect of putting more weight on the front wheel.
I gather that this problem is not fussy about which bike it affects, nor what type of frame or fork. It has something to do with frame and steering geometry, weight transfer, etc, and perhaps the position of the planets. To put it simply, it varies from bike to bike.

The thought has just occurred to me - how many of us actually have the patience to sit down for half and hour and balance the wheels?  By tying or glueing lead or solder to some of the spokes until the wheel, when spun freely, will not stop in the same position twice. Start on two spokes at the rim, opposite the valve. I haven't done this for years, simply because I don't do those speeds anymore  :-(

 

[Flyer]

Hi. This topic came up some months ago on one of the U.S. bike lists, and the responses were very good. One chap had his family filming from the back of their vehicle in front of him when his bike went into its violent wobble. At speed.

This phenonemon used to be known in motorcycle circles as *'tank slappers', for the handlebars would often be banging on the petrol tank. They were also often terminal. One way to get out of it, perhaps the only survival method, was to push forward on the bars, if poss., and accelerate. Bit hard on a bicycle, but you can lean forward and start pedalling again.
This has the effect of putting more weight on the front wheel.
I gather that this problem is not fussy about which bike it affects, nor what type of frame or fork. It has something to do with frame and steering geometry, weight transfer, etc, and perhaps the position of the planets. To put it simply, it varies from bike to bike.

The thought has just occurred to me - how many of us actually have the patience to sit down for half and hour and balance the wheels? *By tying or glueing lead or solder to some of the spokes until the wheel, when spun freely, will not stop in the same position twice. Start on two spokes at the rim, opposite the valve. I haven't done this for years, simply because I don't do those speeds anymore *:-(

eeww

 

[dhk2]

I'm one who has spent time balancing wheels. We have a lot of high-speed descents here (eg, 65 kph plus) and I like to have both tires firmly in contact with the road at those speeds , not to mention the smoother ride. For my rims, which like many others are joined with steel pins opposite the valve holes, I had to add weights next to the valve stem, not opposite as you suggest. A quick way to check for rim balance is simply to put the bike in a stand and spin up the rear wheel in a big gear. If the seat post is bouncing up and down more than a cm, I think some balancing is worthwhile.

 

[Bigbananabike]

If I ride at around 35kph+ with no hands on the bars, my bars shake really bad. Does anyone know what could be causing this?

The bike is a cannondale with carbon folks.....

This is a JOKE right?
Put you bloody hands back on the bars and keep riding

 

[Phill P]

I agree. It is your bike telling you to not be stupid and ride with your hands on the bars.

I've seen racers doing similar speeds hands free to put on/take of rain jackets. Scares the **** out of me just watching!