I was just wondering what purpose it serves, and what is it called, and also do I really need it.

They're officially called "wheel protectors". They're needed if and only if the rear derailleur stop is not properly adjusted and the derailleur shifts the chain off the largest cog into the spokes. If that happens, either the wheel stops instantly, or there is a loud crunching noise and then spokes start to break.

I personally call them "Dork Discs" and have removed them from all my bikes. If you properly adjust your derailleur, you don't need them.

If you're a manufacturer, then you'll insist on having them on for liability and warranty purposes.

Really, it's your call, if you remove them, then you assume the responsibility of your actions. I don't like the way they look and they do nothing for me, so I removed mine! I think the wheel looks "cleaner" without em.

If you don't mind how they look, they only weigh a few ounces and will not adversly affect the operation of your bike.

L8R

If you mean the plastic mounted on the spokes it is a spoke protector. It is made to protect the spokes if/when your chain flies off the large cog into the wheel.

It is a little insurance for the spokes when your derailleur gets out of adjustment.

I concur with L8R, if you have good equipment, keep it in proper adjustment, and shift into the largest cog only when going slowly (which is the only time you need it, anyway!). On most rides, my largest cog, which I keep in reserve for that last big hill after I "bonk," is my spoke protector.

You do need a Dork Disc if you have an ancient bandspring Simplex Tour de France derailleur. Because of the reverse shift pattern, snapping the shift cable can will throw the cage and chain toward, and possibly into, the spokes. Most Campagnolo Cambio Corsas came with, and apparently needed, Dork Discs, as well.

The only disadvantage of Dork Disc-ectomy is that it moves your cogset a couple of mm toward the centerline of the bike, which will degrade your chainline in the larger cogs and chainrings, although it will improve your small - small combinations.

By the way, if you are converting from a standard-space 6-speed to a 7-speed freewheel, removing the disc will give you a welcome 2mm of additional cog-to-frame clearance.

Spoke protectors are designed specifically for the spoke count of your wheels and tooth count of your largest cog. They shouldn't affect a cassette's positioning on the free hub shell if properly selected. That is the way it is on nonretro bikes at least.

Loosescrews.com sells them.

https://www.thethirdhand.com/index.cgi

You can do a search on spoke protectors and a variety will pop up.

A2, I didn't try a search on dork disks.

I say keep the wheel protectors on.

SUUUUURE, you can adjust your derailure correctly and ride around like a smarty-pants without a wheel protector.

However, one day when you are not looking, your bike will fall over or some kid will kick the derailure or some odd thing will happen that will bend your derailure mounting.

Then, you will get on you bike, ride along, switch gears and BOING, clink, clank, TWANG, you will be stopped by the derailure tearing the spokes out of your rear wheel.

Couldn't happen? It happened to me just as I was to embark on a week long European tour. There I was having a nice warm-up day in Switzerland. Fortunately, I brought spare spokes and tools with me. It only took a half day to fix that mess. And, of course, the rear derailure never worked well after that.

OUCH!!!!
I took mine off only because when i last went on a trail by my house, i crashed and broke it (don't ask me how. . . . dont fully know) so i got that all checked out and then never put a new one on. I don't think that you really need one. How often do you have a kid kick that spot?? when i crash i always check over that stuff so im not scared that it will brake on me!

Jared

Hm. My favourite guy at my LBS took off my dork disc when we repaired my bike together. He said they were for amateurs... Haven’t thought of Mike’s point.

I had a disc in the front too. It fell off maybe ten times before I hit the asphalt so badly it was totally trashed. A happy moment.

I don't have one, but I can't remember the last time I used my biggest cog anyway. I feel the same way about these things as I do about ramping on chainrings.