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I was given a 21 gear mountain bike as payment for some work I did for a neighbor which had been in his backyard for about a year. Though it cleaned up very well there is one part I would love to replace: On the back rim, there's a plastic piece separating the seven gear sprocket and the spokes. It's pretty beat up.

Is it hard to replace, and can you tell me how? I'm no bike mechanic, but have gotten my hands dirty.

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    Why are you worried about that part? You just need to remove the cassette / freewheel. It requires a couple tools. parktool.com/category/freewheel-cassette
    – paparazzo
    Commented Mar 28, 2015 at 13:18
  • Actually, you could probably remove it without removing the cassette by just cutting it with a good pair of shears.
    – Carey Gregory
    Commented Mar 28, 2015 at 20:59
  • That is generally known as the "spoke protector" or "spoke guard". You need the appropriate tools to remove the cassette/freewheel. Or a bike shop can probably do it in ten minutes or less. (I do recommend having the spoke protector, even though it's often said to be "unnecessary", since if you do happen to need it due to, say, hitting something with your derailer, it can prevent a nasty fall and easily $100 worth of damage.)
    – Daniel R Hicks
    Commented Mar 28, 2015 at 21:48
  • Basically, if the derailleur (the thing that keeps the chain under tension and shifts the gears) or the chain goes into the spokes of the rear wheel, it can mangle and break spokes and do a bunch of damage which is not cheap. The spoke protector is supposed to prevent this to some extent. It isn't a strictly necessary part, but its nice to have (especially on bikes which are not necessarily well adjusted).
    – Batman
    Commented Mar 29, 2015 at 2:52
  • Another name for the plastic circle is "dork disk"
    – Criggie ♦
    Commented Sep 3, 2019 at 7:43

4 Answers 4

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This is called the spoke guard and prevents the chain from getting tangled in the spokes if the rear derailleur is improperly adjusted.

Properly adjust your rear derailleur and you will have no need for the spoke guard and can throw it away.

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Since the guard is "beat up" it seems to have been doing it's job.

So the derailleur is, or was, out of adjustment. Making sure the derailleur is properly adjusted is the first thing to do. The next thing is to ride the bike for some weeks to see if it stays adjusted.

If the derailleur stays adjusted then you could remove the spoke guard rather than replace it.

But if you have any doubts about it then keep it. If the derailleur gets caught in the spokes then it can be ruined, along with a bunch of spokes.

Answering your direct question is difficult without a photo, because different tools are needed for different bikes. So take it to a shop for this.

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  • These guards get "beat up" on their own. They get dirty from road spray, yellow from UV light and crack.
    – Kaz
    Commented Sep 3, 2019 at 23:55
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This is easy enough, but you'll need some basic hand tools, and either a cassette lockring tool OR a freewheel tool, and probably a chainwhip.

  1. Drop the rear wheel from the bike.
  2. Clean it (optional but makes everything else easier)
  3. Remove the QR skewer or the wheel nut on the drive side.
  4. Cogs removal:
    4a. Use the special tool to undo the cassette's lockring and then slide the cassette off.
    4b. If you have a freehweel then its a different tool, and you spin the whole freewheel+cogs off.
  5. Once that's clear you can see the plastic spoke protector which is often clipped to three or four of the spokes. Unclip it and it will some right off, or snap in the process. Either way its for the bin.
  6. The new spoke protector should clip straight into place, even if its subtly different in design.

Reassemble is basically the reverse process.

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Easy but you need a special tool for extracting the gears, and there is not a standard one, brands have different, it is a job for a bike shop, I'm afraid, but should be inexpensive

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  • The one problem I noticed is that the bike shops have the 'is not needed' approach and just do not add the protector when working on the bike. (Happened to me with several different bike shops.)
    – Willeke ♦
    Commented Sep 3, 2019 at 15:34

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