bike feeling unsteady

landscapingsam
landscapingsam Posts: 174
edited February 2009 in Road beginners
currently riding a giant scr3 and never had any prob with it but just recently it has started felling unsteady when going down hill? could there be any reason for this? hubs seem ok, wheels are true. i questioned this at my LBS and he said everything was fine, i questioned the spoke tension but he also thought this was ok. being a novice i didnt want to argue with him but i can flex my rear wheel by hand if i lean on the saddle and move the top of the rear.

could this be it or am i barking up the wrong tree?

thanks

Comments

  • peanut
    peanut Posts: 1,373
    well the easy way to check is to swop wheels and try it.
    I cannot flex my MA3's 32hole at all . What pressure do you run your tyres at? try some more pressure ie 110lbs
    put your foot on the BB from the side and see how easily it is to deflect the bottom of the frame . I can only push mine 1/4 " with a lot of pressure

    There are a limited No of reasons that could cause this. Check the frame all over carefully for cracks. Put the front brake on lean your weight on the saddle and try to rock the bike back and forward to check the headset.
  • trickeyja
    trickeyja Posts: 202
    Sounds to me like you might have a case of "speed wobble" or "shimmy".

    At speeds of about say, 30-35mph on some setups rapid side to side vibration can occur and can make it very unstable. I had an unpleasant experience on one of my first bikes when this happened and I fell off the bike at about 30mph. I am not sure about how this can be remedied but it might be worth explaining the problem to your LBS or another bike shop.

    You can read about it here:
    http://en.wikipedia.org/wiki/Speed_wobble
    http://www.pro-am.com.au/speed_wobble_on_a_bicycle.htm

    Is this what you are experiencing?
  • Not Another Hill
    Not Another Hill Posts: 382
    Not the wind, is it? My bikes handle quite poorly in breezy conditions but are fine in stiller conditions.
  • landscapingsam
    landscapingsam Posts: 174
    those articles seem spot on, cant understand why it hasnt effected me before though? maybe i have changed the way i ride.

    in most instances i dont actually achieve a full on speed wobble but i feel that the symtoms would develop into one. got some new wheels on the way so will try these and see how i get on!

    thank you for all your help

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