What's that bit of plastic for on the back wheel?

p9uma
p9uma Posts: 565
edited May 2012 in Road beginners
Between the rear cassette and the spokes there is a clear plastic disc on the rear wheel on mine and my wife's bike. What's that for then? I have had a look at a load of photos tonight of bikes in magazines and on the trek website and I can't find the plastic disk on any of them.
Trek Madone 3.5
Whyte Coniston
1970 Dawes Kingpin

Comments

  • thefd
    thefd Posts: 1,021
    Its to keep the chain from falling between the cassette and the spokes/hub. And to stop the chain destroying the spokes and possibly the hub.
    2017 - Caadx
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  • p9uma
    p9uma Posts: 565
    TheFD wrote:
    Its to keep the chain from falling between the cassette and the spokes/hub. And to stop the chain destroying the spokes and possibly the hub.

    Ok, fair enough, I sort of guessed that I suppose, but how come not one single picture of a bike in the latest cycling plus magazine has one of these on the rear wheel? If its that important why don't all bikes advertised and featured have them?

    Also if the rear mech is properly indexed surely that makes the plastic disk redundant.
    Trek Madone 3.5
    Whyte Coniston
    1970 Dawes Kingpin
  • crescent
    crescent Posts: 1,201
    It prevents the rear derailleur from coming into contact with the wheel / spokes. If the derailleur is adjusted correctly it shouldn't be a problem. Often referred to as dork discs by the 'serious' cycling fraternity they are generally perceived to be the devil's work and the first thing that most people remove.

    Cheers
    Bianchi ImpulsoBMC Teammachine SLR02 01Trek Domane AL3“When I see an adult on a bicycle, I do not despair for the future of the human race. “ ~H.G. Wells Edit - "Unless it's a BMX"
  • p9uma
    p9uma Posts: 565
    Crescent wrote:
    It prevents the rear derailleur from coming into contact with the wheel / spokes. If the derailleur is adjusted correctly it shouldn't be a problem. Often referred to as dork discs by the 'serious' cycling fraternity they are generally perceived to be the devil's work and the first thing that most people remove.

    Cheers


    Right then, they are coming right off first thing tomorrow. They look poo.
    Trek Madone 3.5
    Whyte Coniston
    1970 Dawes Kingpin
  • itboffin
    itboffin Posts: 20,061
    Dont throw it away there's a fella on here called NapD and he loves them, I think he has some kind of dork disc collection shrine thing going on.
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  • The discs are more useful for non-indexed geared bikes, because a little more lever throw can pull the chain into the spokes (which has happened to me before on an old Schwinn, which was bad). But with the indexed shifting nowadays, there really isn't any use for them, except for liability issues possibly.
  • team47b
    team47b Posts: 6,425
    Crescent wrote:
    Often referred to as dork discs by the 'serious' cycling fraternity they are generally perceived to be the devil's work and the first thing that most people remove.

    There is one of these on my hybrid but not on my Cube road bike, so it's official then, hybrids are for dorks :oops:
    my isetta is a 300cc bike
  • bompington
    bompington Posts: 7,674
    The discs are more useful for non-indexed geared bikes, because a little more lever throw can pull the chain into the spokes (which has happened to me before on an old Schwinn, which was bad). But with the indexed shifting nowadays, there really isn't any use for them, except for liability issues possibly.
    Bottom stop screw on the rear mech is actually what you need to have properly adjusted, because that will stay in the same place even if your indexing slips with cable stretch etc. And then it doesn't matter if you have non-indexed gears - the Rusty Raleigh, which has had constant issues with the indexing failing on its good ol' downtube shifters to the extent that I just live with friction shifting these days, hasn't ever had the chain slip off the inside.

    But, as the name suggests and as several posters have hinted, the real purpose of a dork disc is to show that you are Not A Real Cyclist.