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Plastic "pie dish"

Catrin2011-03-19 18:14:57 +0000 #1
My LHT has this round piece of plastic behind the rear cassette. What is the purpose of this? Does it protect the cassette?
OakLeaf2011-03-19 18:30:33 +0000 #2
It's there in case the chain would come off and get stuck between the cassette and the spokes. If that would happen, the wheel would seize.

It's a very rare occurrence, since the low limit screw on the RD as well as the whole design of a derailleur system should prevent it. Still, if it does happen it could be catastrophic, which is why manufacturers are required to put the pie plate on. But they're at best messy, and at worst clattery and noisy, which is why most people take them off.

There's also a bit of peer pressure, as they're considered geeky, but obviously that's no reason to do anything; and weight weenies like to save the couple of dozen grams.

I'd ignore it unless it's making noise or making it unreasonably hard to clean your cassette.
Muirenn2011-03-19 18:24:15 +0000 #3
I've never bothered about them. I've got 3 bikes and 3 pie plates
nscrbug2011-03-19 19:34:07 +0000 #4
Quote:

Originally Posted by OakLeaf

It's there in case the chain would come off and get stuck between the cassette and the spokes. If that would happen, the wheel would seize.

It's a very rare occurrence, since the high limit screw on the RD as well as the whole design of a derailleur system should prevent it. Still, if it does happen it could be catastrophic, which is why manufacturers are required to put the pie plate on. But they're at best messy, and at worst clattery and noisy, which is why most people take them off.

There's also a bit of peer pressure, as they're considered geeky, but obviously that's no reason to do anything; and weight weenies like to save the couple of dozen grams.

I'd ignore it unless it's making noise or making it unreasonably hard to clean your cassette.

This actually happened to ME...so I speak from experience. My chain did fall into the spokes as I was trying to downshift into an easier gear while climbing a hill. The wheel did seize, but luckily I had unclipped beforehand and was able to avoid, what could have been a nasty fall. This happened on my Cervelo, which already had the "dork disk" removed. My current Cannondale, also had it removed before I took the bike home. But my "backup" Trek bike, still has it...and I have no intentions of removing it.
Owlie2011-03-19 19:52:29 +0000 #5
It's never bothered me. I just left it. But then, I'm a "road geek."
ny biker2011-03-19 19:08:21 +0000 #6
My new bike has one but it's small and black so it's not too noticeable. I'm not planning to remove it.

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