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  1. #1
    Senior Member Sir Lunch-a-lot's Avatar
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    Rear Deraileur Clearance Question

    Hello. I was working on getting my bike all tuned up today, and I was setting the rear deraileur adjustments (since I replaced the last one and the chain and the front sprockets, I didn't have my full gear range). It all shifts pretty well now, but I was wondering: How much clearance should I have between the deraileur "swing arm" and the spokes when in the lowest gear? Right now, I have it so that it is roughly 1cm clearance, but I am worried that if my wheel goes out of alignment and starts wobbling that the arm will snag in the spokes and get torn to shreds just like the last two I had (this is the problem I am trying to avoid this time around).
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  2. #2
    hello roadfix's Avatar
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    You're the perfect candidate for the 'dork disc'. Make sure you install one...

    Anyway, as long as your derailleur limit set screws are set correctly, you should be ok....
    Now, why would your rear wheel 'get out of alignment'?
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  3. #3
    jur
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    You're lucky with 1cm; my bike came back from the LBS after 1st service with the RD actually touching the spokes in low gear! I adjusted the lo screw, now there is perhaps 3mm.
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  4. #4
    Senior Member DieselDan's Avatar
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    Mine is about 5mm off the spokes (RSX 7 speed hub, 36 spoke with CXP-10 rim). Your rear wheel will rub the brake before the RD if it gets out of true. You SHOULD make sure the rear wheel is properly aligned BEFORE you ride the bike.

    Alignment and trueness are two DIFFERENT things.
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  5. #5
    You need a new bike supcom's Avatar
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    I believe your rim would have to go way, way out of true to put the spokes against the rear derailleur. The rear derailleur should be oriented vertically and directly below the selected cog. If it's not, then your hanger may be bent or, less likely, your wheel is not dished properly.

    EDIT: That last sentance makes no sense. Let's try this instead:

    If the rear derailleur is not directly below the selected cog and vertically oriented, you may have a bent derailleur hanger. If it is correctly positioned and real close to the spokes (measure someone else's wheel for reference), then your wheel may not be properly dished.

    That should make better sense.

  6. #6
    Senior Member Sir Lunch-a-lot's Avatar
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    Quote Originally Posted by The Fixer
    You're the perfect candidate for the 'dork disc'. Make sure you install one...

    Anyway, as long as your derailleur limit set screws are set correctly, you should be ok....
    Now, why would your rear wheel 'get out of alignment'?
    You've lost me on the 'dork disc' (would that be that funny clear disc between the rear sprockets and the spokes, or would it be some sort of lude reference/insult to ones intelligence, or something else all together?). My rear wheel would get out of alignment if say... one of the nuts holding the wheel in place got loose or something, allowing one side of the axle to slide forward whilst the otherone remains fixed.


    But... if some of you guys are going with 3-5mm, then a 10mm clearance (thats an eyeballed guestimate btw) should be good. (I guess that definitively means that on the last deraileur I had the limiters were way out of whack to allow my deraileur to catch) So, I guess that means I am good to go (for now). Thanks for the info guys.
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  7. #7
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    Yeah, "dork disk" is the somewhat insulting name for the plastic or metal disk between the largest cog and the spokes. It protects the spokes if the chain gets spilled but is considered unnecessary if your shifting is set up properly. It won't protect the spokes from hitting the derailleur since it isn't that big.

    Your wheel should never come loose. If you have a quick release hub and the skewer is properly tightened the wheel will not move. If it is a nutted hub and the nuts are tight, the wheel won't move. If you have vertical dropouts the wheel really can't move except to fall out downwards. If this problem has happened to you twice in the past, you are doing something very wrong.

  8. #8
    hello roadfix's Avatar
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    Quote Originally Posted by Sir Lunch-a-lot
    You've lost me on the 'dork disc' (would that be that funny clear disc between the rear sprockets and the spokes, or would it be some sort of lude reference/insult to ones intelligence, or something else all together?)
    No, it's nothing personal. It's a common term and joked about item here...

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  9. #9
    Senior Member Sir Lunch-a-lot's Avatar
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    Quote Originally Posted by HillRider
    Your wheel should never come loose. If you have a quick release hub and the skewer is properly tightened the wheel will not move. If it is a nutted hub and the nuts are tight, the wheel won't move. If you have vertical dropouts the wheel really can't move except to fall out downwards. If this problem has happened to you twice in the past, you are doing something very wrong.
    I am pretty sure that wheel alignment was not the ultimate cause. It may have just been a contributing factor. I must have just set my limiters very wrong (and its possible that I had made other adjustments to the wheel and didn't align it properly in one of the instances), and then they all added up with me overshifting or something and... krunch! So, I suppose that the best thing to do is just do a "once over" before ever ride to ensure that nothing has mysteriously gone out of whack (whether it results from my own carelessness, or sabatoge...)

    Now that my settings are all set and happy, I went to take my bike for a winter bike ride to school this morning... only to discover that it sprung yet another leak in the self sealing back tire. (My guess is that this was due to not allowing the patch enough time to cure at room temperature before sending the bike back out to the sub zero weather outside. I also discovered yesterday that the self sealing feature seems to only work in warm weather... perhaps obvious things, but sometimes it takes a while to learn them). So... I'll have to have a look at that patch... and... yeah. Thanks for all your help guys.
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