Anybody ever pop out a front wheel due to disc brakes?- Mtbr.com
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  1. #1
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    Anybody ever pop out a front wheel due to disc brakes?

    There is a small group of people on usenet who warn that the forces applied by a disc brake tends to push the axle downwards. I guess that makes sense... I think one of them even has a web page detailing the HORRORS of this, and even a story about a guy that DIED!!! OH NOES!1!!1!! Has anybody had a wheel pop out on them due to this? Or at least if the axel moved a bit... I'm wondering if I should be paranoid and crank down the QR really tight, or whether this is no big deal. I think one can get bigger rotors (e.g. 8"), but that will only make the problem slightly less bad. How about grippier nuts on the QR?

    I have an older Marzocchi fork, with fairly minimal lawyer tabs.
    Last edited by beanbag; 12-03-2005 at 04:50 AM.

  2. #2
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    I haven't had any problems with the axle falling out.

    As long as you fasten the QR correctly, it shouldn't be a problem. I don't know which fork you have, but on most forks the dropout has some sort of "lips" around the qr-ends. This means that you qould have to have the qr really loose before it will slip trough, and by that time, you will probably have noticed the loose wheel.


    Of course, you could go 20mm-axle like quite a few people do nowadays. In my case this means King 20mm/Pike Race in front, and King HD with FunBolts in the rear.

  3. #3
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    I wonder...

    Quote Originally Posted by beanbag
    There is a small group of people on usenet who warn that the forces applied by a disc brake tends to push the axle downwards. I guess that makes sense... I think one of them even has a web page detailing the HORRORS of this, and even a story about a guy that DIED!!! OH NOES!1!!1!! Has anybody had a wheel pop out on them due to this? Or at least if the axel moved a bit... I'm wondering if I should be paranoid and crank down the QR really tight, or whether this is no big deal.
    I wonder if someone had their front wheel off and then put it back on. After tightening up, the disc rubbed and they loosened up a little too much and the wheel came off. I haven't any problems, but sometimes when I flat and put the wheel back on, it rubs. I have to back off a little to clear the disc. I do tend to over tighten. There is some kind of washer device that enables you to tighten the QR at the same place, before you removed the wheel. I started just laying the bike down in my pickup so I wouldn't have to remove the front wheel when transporting.
    Don

  4. #4
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    The only problem that I have had....

    with QR loosening with disc brakes have been with the Specialized Stout and Scraxle hubs. But I believe that this has more to do with the axle and QR being a one piece intergrated part as opposed to the more tradtitional axle/skewer. I've always used a qr with a high camining action, like Shimano, Hope, or Salsa (to name a few) and have had no problems. I do tend to tighten them to a point that would be consdered "over tightening" by most I suppose. But I have never had a problem with loosening QR's and disc brakes. I've read the articles that you are talking about. They have made me cautious and more observant of how my front end is acting. But there is more there than is being told I think. I just don't think we're getting all the data. There are no specific brands indicated for brakes, OR's, hubs, etc. That and this seems to be happening to larger diameter rotored discs, and there seems to be a correlation between riding style as well. And where is the correlated information? There just isn't enough data to support the alligations that are being made. Plus it seems to be a very rare occurance, and spotty as to who has suffered this malady. The seeming randomness of the incident seems to indicate more of an operator problem that an one of equipment. If this is a problem with forks, then why not the rear as well? The same forces are present at the rear. Anyway, it has made me more consious of my QR's. I check them before every ride and during the ride at stops. Like I said, I've had no problems so far, except as stated above. My recommendation would be to re-read the articles in question and be aware that it is possible. Do your preride checks religiously and check em during the ride at any rest stop. There are WAY to many people running disc brakes with standard QR's that are not having any problems to make me think this is some grand conspiricy to keep from spending money on the part of fork manufacturers. Just be aware that there COULD be a problem and watch out for it. The old saying, "forewarned is forearmed" comes to mind.

    Good Dirt

    Good Dirt
    Last edited by Squash; 12-03-2005 at 08:17 AM.
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  5. #5
    TNC
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    I have a Super Jr. w/QR axle.

    Quote Originally Posted by beanbag
    There is a small group of people on usenet who warn that the forces applied by a disc brake tends to push the axle downwards. I guess that makes sense... I think one of them even has a web page detailing the HORRORS of this, and even a story about a guy that DIED!!! OH NOES!1!!1!! Has anybody had a wheel pop out on them due to this? Or at least if the axel moved a bit... I'm wondering if I should be paranoid and crank down the QR really tight, or whether this is no big deal. I think one can get bigger rotors (e.g. 8"), but that will only make the problem slightly less bad. How about grippier nuts on the QR?

    I have an older Marzocchi fork, with fairly minimal lawyer tabs.
    This fork, brake, and bike combo would probably represent all the potential worst elements about what you're asking. This 6.75" travel '02 Jr. T came with standard QR dropouts...a real oddity nowdays. I put Super T cartridges in the fork, and it is a really nice piece of suspension action. I run an 8" rotor on it, and the whole deal was on a Bullit that got used for the "hard" stuff either locally, or in Moab, or in other big hit riding venues. Riding buddies who are even harder riders than me have pounded on this setup. Using Shimano XT skewers on the QR, and I've never had so much as even a loosening issue. Since going to a 20mm fork on the bike, I do notice a slight improvement in steering precision in severe rock gardens...but not a night/day comparison.

    One think I've seen in past posts about older Marzocchi forks worth mentioning. Up to a certain point in year models, some older Zokes actually had hollow, open, thin walled areas in their lowers that extended below the axle point. There are pics of some of these actually torn or ripped at the bottom of the fork. I'd bet that most of them were the result of a bad landing or other disaster rather than 8" rotor force. I did think that this was a dumb idea, leaving that area hollow and open like that. Maybe should have been "capped off" at least to strengthen the lower. Otherwise I wouldn't be too fearful of running an 8" rotor on a QR fork unless I was in to really big air or aggressive hucking.
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    Last edited by TNC; 12-03-2005 at 09:05 AM. Reason: add pic

  6. #6
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    The other thing I don't understand is why people think the problem is worse with larger rotors. I think the problem is reduced with larger rotors. Since the brake pad is further out from the center, less forces are required to generate the same braking torque.

  7. #7
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    I haven't had the axle pull out but I have had it move in the drop-outs on my first disc-brake bike. Make sure the QR is super-tight--much tighter than you would need for V-brakes. And XT skewers work pretty good compared to the no-names that usually come with a bike (E-Bay--$12).

    You should never have to mess with the tightness to get rid of disk brake rub. The axle will only let the fork (and hence the caliper) "pinch" in so far when you tighten it--unless you're super-man and can start bending metal. To get the rotor not to rub make sure you put the axle back in the same spot every time. Mark the cone nuts with a paint, a marker, or file a mark in it. Orient it the same way everytime you mount the wheel. The first time you do this you may have to re-adjust the caliper but after that you're golden.

  8. #8
    jrm
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    I've looked down and saw the QR flappin

    but even though i used the front brake to stop the wheel never came out fo the dropouts...

  9. #9
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    I have the XT hub with the 6 rotor bolt holes. The serrations on the QR looked pretty flimsy, so I changed it with an LX QR from back in '95. I also put a dab of white nail polish between the QR nut and the dropout to check for any movement. I rode up and down the street hitting the brakes, and so far there is no movement.

    Does anybody know of any mechanisms or devices that can help secure the axel more securely in the dropout (besides buying a thru axle)? One idea is a plate with a hole on one end that the axel goes thru, and the other end clamps on the fork leg. Another idea is to use my v-brake post and have something like a non-pivoting arm such that if the wheel starts to come out, the rim will hit that first. I know this sounds kind of stupid, but I'd rather not have to worry about a wheel falling off.

  10. #10

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    Quote Originally Posted by beanbag
    I have the XT hub with the 6 rotor bolt holes. The serrations on the QR looked pretty flimsy, so I changed it with an LX QR from back in '95. I also put a dab of white nail polish between the QR nut and the dropout to check for any movement. I rode up and down the street hitting the brakes, and so far there is no movement.

    Does anybody know of any mechanisms or devices that can help secure the axel more securely in the dropout (besides buying a thru axle)? One idea is a plate with a hole on one end that the axel goes thru, and the other end clamps on the fork leg. Another idea is to use my v-brake post and have something like a non-pivoting arm such that if the wheel starts to come out, the rim will hit that first. I know this sounds kind of stupid, but I'd rather not have to worry about a wheel falling off.
    Yes, you can modify your front hub to a BMX solid axle for $11. I would never worry about one of those falling off ever. They are the ones with nuts on the ends, not QR.

    Worth it if you don't take your front wheel off every ride.

  11. #11
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    Quote Originally Posted by Squash
    with QR loosening with disc brakes have been with the Specialized Stout and Scraxle hubs.

    Good Dirt
    My girl friend's bike has this problem with her Specialized front hub. I have to actually tighten the nuts that hold the hub together after a while. I can tighten them, crank down the qr and several miles into the ride that stuff is loose again to the point where the wheel has noticeanle play in it. At the top of the wheel I can sometime move it 1/4 inch back and forth. Not a comfortable feeling knowing something could come too loose... That hub is going to go if I can't find a permanent fix for it soon.

    -Dan

  12. #12
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    I've had an axle shift in the dropout once or twice but I'm sure that I was just sloppy when tightening the QR those times. It wasn't a big deal but it did change my opinion about lawyer tabs. Regarding your fork, I doubt it would take much of a tab to keep the wheel in if it did slip. I wouldn't worry about it.
    "The mouth of justice contemplates wisdom."

  13. #13
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    Quote Originally Posted by beanbag
    I have the XT hub with the 6 rotor bolt holes. The serrations on the QR looked pretty flimsy, so I changed it with an LX QR from back in '95. I also put a dab of white nail polish between the QR nut and the dropout to check for any movement. I rode up and down the street hitting the brakes, and so far there is no movement.

    Does anybody know of any mechanisms or devices that can help secure the axel more securely in the dropout (besides buying a thru axle)? One idea is a plate with a hole on one end that the axel goes thru, and the other end clamps on the fork leg. Another idea is to use my v-brake post and have something like a non-pivoting arm such that if the wheel starts to come out, the rim will hit that first. I know this sounds kind of stupid, but I'd rather not have to worry about a wheel falling off.

    You could make some threads inside the axle and use steel bolts. This will also make the front slightly stiffer.

  14. #14

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    Quote Originally Posted by Mr_Kaizer
    You could make some threads inside the axle and use steel bolts. This will also make the front slightly stiffer.
    Actually, do what I did onc when we busted a QR before a run.

    Go to a hardware store and look at the threaded small rebar they sell. The smallest one they sell fits perefectly into the hole where the QR goes through the hub. You can then use washers and nuts to tighten it into there. It works well.

  15. #15
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    So I went riding today...

    I put a drop of white paint on the QR nubs to check if there was any movement. My riding style is not really to blast down hills, but creep down very slowly. BTW, I really like how disc brakes let you drag the brake down a hill and not fade. So far I noticed no movement, so that is good.

  16. #16
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    Quote Originally Posted by dan51
    My girl friend's bike has this problem with her Specialized front hub. I have to actually tighten the nuts that hold the hub together after a while. I can tighten them, crank down the qr and several miles into the ride that stuff is loose again to the point where the wheel has noticeanle play in it. At the top of the wheel I can sometime move it 1/4 inch back and forth. Not a comfortable feeling knowing something could come too loose... That hub is going to go if I can't find a permanent fix for it soon.

    -Dan
    You'd better fix that soon before your gf gets hurt...... then you'll have to answer to the law, if you know what I mean

  17. #17
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    A good skewer with sharp teeth and a steel axle works fine. Shimano XT and Salsa are my favorites. Never had a problem with either, running 8" rotors and long rough descents.

    The calculations James makes include some fundamental errors, showing a flawed understanding of rotational dynamics (radial forces cannot be balanced by tangential forces!). This leads him to a conclusion that a mtb disc brake can generate a downward force in the range of 10-20 g's (10-20 times the force of gravity). Jet pilots with pressure suits go unconscious around 9 g's, and 20 g's would launch you over the trees.

  18. #18
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    I am relatively new to disc brakes and my bike has King hubs, Magura Marta brakes, Salsa QR, F100X fork and I have had lots of problems with the Salsa QR coming losing. I get it as tight as I can, then after a while I will hear and feel the looseness and will stop and tighten it again. The rear never does this. I have no idea what is causing this.

  19. #19
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    Quote Originally Posted by lemmy999
    I am relatively new to disc brakes and my bike has King hubs, Magura Marta brakes, Salsa QR, F100X fork and I have had lots of problems with the Salsa QR coming losing. I get it as tight as I can, then after a while I will hear and feel the looseness and will stop and tighten it again. The rear never does this. I have no idea what is causing this.
    I think it was stated that the slight bending forces created by the disc brake very slowly loosen the QR. I would stop riding until I got a QR that doesn't come loose.

  20. #20
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    You may have a Salsa titanium QR skewer -- ti is completely inappropriate for a QR rod on a suspension fork because it's too stretchy.

    Get a new XT QR for ~$15, or a new set of Salsa stainless steel QRs for ~$50, and your problem should be solved.

  21. #21
    YRTRNRSHVY
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    Quote Originally Posted by watermoccasin
    You may have a Salsa titanium QR skewer -- ti is completely inappropriate for a QR rod on a suspension fork because it's too stretchy.

    Get a new XT QR for ~$15, or a new set of Salsa stainless steel QRs for ~$50, and your problem should be solved.
    Mine are the stainless Salsa skewers. I weighed them and one was 50g and the other was 56g which is what the chro-mo ones are supposed to weigh.

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