StevenAkaProek

https://static.howstuffworks.com/gif/bicycle-2a.jpg

that plastic thing? Went riding with my girlfriend and she noticed something was hitting her rear tire. We checked breaks and everything was fine. We then noticed that little plastic thing was cracked and hitting the cog set

Taking it to our LBS tomm, what's the bike part name? and is it expensive?

thanks sorry newb

Update: Spoke guard? I read it's not needed, do we just remove it?

CCrew

The picture is of a cassette..unless you're referring to the plastic shield behind it. That's generally called a "dork disc"

theREEDeffect

It's known informally as a "dork disk", and it's meant to prevent the chain and rear derailleur from traveling into the spokes.

valleycyclist

You or the bike shop can adjust your rear derailleur if necessary. Once it is adjusted correctly, you can safely remove the disk.

Velo Dog

Technically true. I don't have them on any of my bikes. And they ARE dorky (it helps to think of them as aerodynamic aids, reducing the drag from the wheel by 0.02 percent).
On the other hand, they don't hurt anything, and if you don't pay much attention to your bike, they WILL keep the derailleur from going into the spokes and breaking them.

ElJamoquio

You can just remove it. If you want a new one, which most people don't, you could probably get one for free, as a cast-off from other bikes. You'll probably have to pay for cassette removal and re-installation, though.

I'd just remove it; but I keep my derailler limits in the proper location.