What is it for?

[Mr Pig]

The clear plastic disk between the largest gear on the cassette and the spokes. I had thought it was maybe there to stop the chain going off the gear into the spokes but the disk on my new bike is smaller than the gear.

Is it just to keep the spokes/hub clean?

The reason I ask is the disk on the bike I'm giving my son is knacked and I'll need a good reason to buy a new one.

 

[dodgy]

You were right in your second sentence (stops the chain colliding with the spokes). Not sure why your disk is smaller than your gears.

I take mine off and ensure the limit screws are set properly.

Dave.

 

[Disgruntled Goat]

A pie plate smaller than the largest cog? That's novel.

 

[Mr Pig]

A pie plate smaller than the largest cog? That's novel.

It is actually smaller than the second largest cog, which is why I was wondering if that's what it was for. If it is there to keep the chain out of the spokes then it obviosly is a bit stupid it being smaller than the gears.

 

[barq]

I take mine off and ensure the limit screws are set properly.

Same, although I had one really unlucky experience where although the limits were correctly set I clipped a fallen tree at speed on my mountain bike which smashed the rear mech through the wheel. I broke numerous spokes and bent the rear triangle of the frame out of shape! That's a rare circumstance where a spoke guard might actually have been some use. However an alternative strategy is not to crash into trees.

 

[ColinJ]

Perhaps it was for a higher-geared cassette (i.e. smaller sprockets) but someone changed the cassette to give easier climbing gears?

 

[Mr Pig]

Perhaps it was for a higher-geared cassette but someone changed gears?

It's a new bike. That's the way it came. I might ask the shop about it or mail the manufacturer Genesis/Ridgback.

 

[ColinJ]

It's a new bike. That's the way it came. I might ask the shop about it or mail the manufacturer Genesis/Ridgback.

When I got my first (adult) road bike, I didn't think I'd get up many Yorkshire hills as a 16+ stone novice cyclist on a 42/24 bottom gear. I got the shop to change the cassette from 12-24 to 13-28 for me before I went to pick the bike up and so I ended up with a plastic disk that was too small. I thought the same might happened to you, but I'd forgotten that your new bike was a MTB. They come with massive bottom sprockets as standard, so they should have massive plastic disks to match.

Okay, I've got another idea... A factory makes both road wheels and MTB wheels. The guy running the MTB wheel machine runs out of MTB-sized plastic disks and asks his mate on the adjacent road wheel machine if he can scrounge a box of his plastic disks to save him going to the stores to get some more .

To be honest, it shouldn't be necessary to have those disks fitted. If the rear endstops are set properly, it is virtually impossible for the chain to fall off the cassette. I took the disk off that first bike of mine. The wheels on my more expensive bikes don't have them so I think that the manufacturers assume that cheaper bikes receive poorer maintenance and fit the disks just to be safe.

Chains do fall off at the front though and you should make sure that the little peg sticking out of the big chainring is behind the righthand crank. It is there to stop the chain getting wedged down between the crank and the chainring. You can get something called a 'Dog Fang' to help prevent a similar problem if the chain falls off the smallest chainring.

 

[RedBike]

I take them off on the road bike; but having just had a similar experiance to Barq I wont be removing it from my MTB wheels in a hurry.

 

[Mr Pig]

I don't think I've ever had the chain come off the big ring, but then maybe that's because of the plastic disk! At any rate I've sent a mail off to Genesis/Ridgback and I think I'll be asking them to send me a bigger disk.

 

[yenrod]

Im actually thinking of putting one back on my bike.

Was riding away from lights once and next min i'm hoping across the road - managed to get a foot out - had to get a taxi home.

 

[Destry]

Seems a shame to use a great big frisbee type thing when that neat little limiting screw does the same job. The first time I saw one was the first time I had a bike with disc brakes, and I always assumed it was to stop oil from spattering the disc brake rotor. I hated it, anyway -- stopped the wheel running free and looked hideous.

A perfect opportunity to lose... er, 10 grams?

Tom

 

[Mr Pig]

Seems a shame to use a great big frisbee type thing when that neat little limiting screw does the same job.

But if your derailier get's clattered towards the wheel that neat little screw ain't going to help you much. And derailier settings can and often do go out. Ten grams might save you a lot of greif.

 

[Destry]

I'm kidding about the weight -- what really annoyed me was that it seemed to stop my wheel running free. One of the great bike-nerdy pleasures in life is putting a bike on a stand, heaving the cranks and enjoying the blur of spokes and the oily hum as the wheel spins for minutes on end. That frisbee thing spoiled it completely for me!

Cheers,

Tom

 

[Mr Pig]

One of the great pleasures in life is heaving the cranks and enjoying the blur of spokes as the wheel spins for minutes on end. That frisbee thing spoiled it completely for me!

Pits eh? You'll just need need to pop a spoon into the foil of a fresh coffee jar and put fresh cotton sheets on your bed to make up for it ;0)