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  1. #1
    Join Date
    Nov 2009
    Location
    Indianapolis, Indiana
    Posts
    10,952

    Plastic "pie dish"

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    My LHT has this round piece of plastic behind the rear cassette. What is the purpose of this? Does it protect the cassette?

  2. #2
    Join Date
    Sep 2007
    Location
    Uncanny Valley
    Posts
    14,645
    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.
    Last edited by OakLeaf; 10-16-2010 at 04:37 PM.
    Speed comes from what you put behind you. - Judi Ketteler

  3. #3
    Join Date
    Jun 2010
    Posts
    6,449
    I've never bothered about them. I've got 3 bikes and 3 pie plates
    So long as the wheels are still turning, life is good.

    Battswebb

    Pinarello Quattro~CAADX~ Zurich Lemond
    Specialized Romin Saddles

    Surly Krampus!

  4. #4
    Join Date
    Jul 2008
    Location
    Chicago suburbs
    Posts
    1,244
    Quote Originally Posted by OakLeaf View Post
    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.
    2012 Seven Axiom SL - Specialized Ruby SL 155

  5. #5
    Join Date
    Apr 2009
    Location
    Tucson, AZ
    Posts
    4,713
    It's never bothered me. I just left it. But then, I'm a "road geek."
    At least I don't leave slime trails.
    http://wholecog.wordpress.com/

    2009 Giant Avail 3 |Specialized Jett 143

    2013 Charge Filter Apex| Specialized Jett 143
    1996(?) Giant Iguana 630|Specialized Riva


    Saving for the next one...

  6. #6
    Join Date
    May 2008
    Location
    northern Virginia
    Posts
    5,828
    My new bike has one but it's small and black so it's not too noticeable. I'm not planning to remove it.

    - Gray Trek Madone 4.7 road bike, mystery crack in top tube repaired by Calfee, Bontrager Affinity RXL saddle
    - Red Trek 6000 mountain bike, Bontrager Evoke WSD saddle

    Gone but not forgotten:
    - Silver Trek 2000 road bike
    - Two awesome and worn out Juliana saddles

  7. #7
    Join Date
    Sep 2010
    Location
    New York, NY
    Posts
    44
    My LBS removed it immediately without asking once I paid for the bike. I think they are so used to roadies asking for it to be taken off, they just do it to save time.

    Took the bike home, and my bike nerd friend went to work removing all the stickers, spoke reflectors and front reflector.

    Went in for a mega bike re-fit a few months ago, and my bike fitter mumbled something about 'looking like a noob' as snatched the rear reflector off as well.

    I asked if this was a bad idea and he noted that the reflector was blocked by my seat pack anyway and I already attach blinky LED lights to the front and back of my bike when I need them (they live in my seat pack at all times).

    All these people dedicated to keeping me from looking like a bike dork, and yet they do this while wearing the tackiest racing kit designs I have ever seen.
    'You can't always get what you want. But if you try sometimes, you'll find you get what you need.' - Mick & Keith

  8. #8
    Join Date
    Oct 2008
    Posts
    355
    it's true. the "pie plate" is one of many, many things bike snobs use to identify a newbie. It's totally unnecessary if your bike is set up correctly, but as a poster noted, it might save your life some day...

    I routinely remove them, and never install them on any of the bikes I sell. That being said, who cares? If it doesn't bother you, it might be your friend some day. Also, if your chain does fall behind your cassette, in addition to potentially seizing the rear wheel it can also really dig into the spokes and compromise/make them weaker as a result. I have seen a lot of drive-side spokes frighteningly compromised from this occurring.

    the one thing I've always disliked about them is that uv exposure turns them brittle, their little clips onto the spokes break as a result, and they become a rattling nuisance. But, otherwise, they are harmless...and weigh approximately 42 grams.
    Last edited by lunacycles; 10-18-2010 at 05:55 PM.

  9. #9
    Join Date
    Apr 2008
    Location
    Texas
    Posts
    905
    Quote Originally Posted by lunacycles View Post
    It's totally unnecessary if your bike is set up correctly
    Exactly.
    And, if you are going a little bit faster you will notice the horrible noise they make...
    E.'s website: www.earchphoto.com

    2005 Bianchi 928C L'Una RC
    2010 BMC SLX01 racemaster
    2008 BMC TT03 Time Machine
    Campy Record and SSM Aspide naked carbon on all bikes

  10. #10
    Join Date
    Apr 2009
    Location
    California
    Posts
    371
    Quote Originally Posted by lunacycles View Post
    Also, if your chain does fall behind your cassette, in addition to potentially seizing the rear wheel it can also really dig into the spokes and compromise/make them weaker as a result. I have seen a lot of drive-side spokes frighteningly compromised from this occurring.
    At the bike co-op where I volunteer, it is a regular occurrence for people to come in with a broken drive side spoke - and when we get the cassette/freewheel removed, all the outer drive side spokes are mangled.

    Quote Originally Posted by lunacycles View Post
    It's totally unnecessary if your bike is set up correctly
    Bikes fall over, derailleur hangers bend; limit screws might be set wrong (because the shifter is set right); twigs can snag in derailleur cables thus changing gears; twigs can snag in chains or a chain can seize, thus causing the derailleur to get pulled into the cogs; and so on. In other words, even when a bike is set up correctly, things happen. It is much better to have just a destroyed derailleur, than a destroyed derailleur and rear wheel.

 

 

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