Plastic Disc Needs Replacing- or not?

[Intelligenthamster]

Have been having trouble with the drivetrain on my 2007 Specialized Rockhopper MTB and on closer inspection can see the plastic disc or shield behind the largest sprocket has cracked and it is pushing against the chain when in low gears. It is going to have to come off.

I also have a 1987 Peugeot road bike which also had one of these discs / shields, which through sheer old age got brittle and warped a couple of years ago. I removed it and I've never noticed any difference, but this bike has the old-fashioned friction shifters on the down tube- a lot less precise than the trigger-shifters on the Spesh. It also stays on the road, whereas the MTB encounters water, clay, bumps and a lot of sand in a typical ride- that's the Sussex Weald for you.

My question is, do I need to replace the disc on the MTB?

 

[wheres_my_beard]

It is going to have to come off.

Yes it is.

It should never be replaced.

 

[marzjennings]

No and it should have come off the day you bought the bike. Same as the reflectors in the spokes.

 

[HLaB]

Its only there to stop a chain riding up into the spokes on a poorly adjusted mech; lots of folk remove them and I don't think it was even fitted to my Bianchi and if it was fitted to the Kinesis it was removed by me.

 

[Intelligenthamster]

Thanks peeps I didn't think it would actually need replacing, especially as the Pug's never missed the one I took off, but always a good idea to consult wiser heads than mine.

 

[cyberknight]

If i am honest i would only take it off a bike when i needed to take the rear gear cassette off , certainly not worth ripping it off for the sake of it even if you do not need it.

 

[Fnaar]

If you paint a spiral pattern on the disc, you can hypnotize people with it... but they have to run alongside your bike, looking at it.

 

[Deleted member 1258]

Its called a pie plate, we used them in the days when there was no index gears, every one was on friction shifters. It was there to protect the spokes if there was a miss change on selecting bottom gear and the chain ended up in the spokes. Its not normally needed with modern indexed gears.

 

[BikeLiker]

If i am honest i would only take it off a bike when i needed to take the rear gear cassette off , certainly not worth ripping it off for the sake of it even if you do not need it.

Mine came off over the cassette without resorting to vandalism - 27 tooth sprocket.

 

[chillyuk]

Funnily enough on my hybrid my chain has gone between the freewheel and spokes a couple of times in the last couple of months and because of the rivet heads on the freewheel the chain jams really hard. I did it again over the weekend and I had to split the chain to pull it free. I have ordered one of these plates to fit and try and reduce further problems. My shifter is set up correctly, and the stop does normally stop the derailleur before the chain goes past the big sprocket. It is a basic SIS mech so I can only assume that under some circumstances or conditions it has sufficient flex or something to allow it to over shift.

 

[Fast_Mark]

Mine came off over the cassette without resorting to vandalism - 27 tooth sprocket.

How did you get it off without employing violence or tools? I hate mine but am resigned to leaving it on there until I have to replace the cassette (I'm not inclined to remove the cassette just to take off the pie plate)