bumping bike on big sprocket

brucebanner
brucebanner Posts: 256
edited September 2010 in Road beginners
why does my bike bump up and down when I'm peddling fast on a somewhat low gear, e.g., biggest chain ring and highest sprocket.

Comments

  • Weejie54
    Weejie54 Posts: 750
    You seem to be describing a 'somewhat high gear'. Do you mean biggest chainring and biggest rear sprocket or smallest rear sprocket? If the former, then it might be that your drivetrain is under duress!
  • daviesee
    daviesee Posts: 6,386
    Sounds like you are mashing the pedals instead of keeping a smooth circular rhythm.
    None of the above should be taken seriously, and certainly not personally.
  • softlad
    softlad Posts: 3,513
    were you on a BMX track..?
  • Stone Glider
    Stone Glider Posts: 1,227
    The classic advice is "big to little, little to big" which ensures a smooth chain line. Despite there appearing to be ten choices on big and little rings it is advisable to only use six or seven of them before changing ring. The point is, Andy, if you are at the large end of the sprocket and try to change onto the big ring you have every chance of your chain jumping off :)
    The older I get the faster I was
  • woodywmb
    woodywmb Posts: 669
    I suspect you're on the biggest chainring (front) and smallest cog (rear). the "hardest" pedalling combination. If you haven't used the smallest sprocket much the likelihood is that it hasn't meshed properly yet with the chain, making the drivetrain noisy and rough.
    All the other cogs will have been broken in and mixing sweetly with your chain because you tend to use the cogs nearer the centre of the cassette. To solve this, drop into the smallest cog as often as you can and stay in that gear combination for many miles. Eventually the teeth on that smallest cog will file down (as all the others will have done) to accommodate the inner plates of a worn, otherwise "engaging", chain.
    http://www.pinkbike.com/photo/1296598/
  • John.T
    John.T Posts: 3,698
    It is because you are pedaling fast but not smoothly. The weight of 2 legs going up and down rather violently is making the bike jump about. Either change up a gear or learn to pedal more smoothly.
    As others have said you should not be using the big / big combination (or small / small). The same ratios are available using the other ring and sprokets closer to the centre of the cassette.
    My Fleet.

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