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  1. #1
    me have long head tube TallRider's Avatar
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    too much exposed axle on a ss mtb hub - worried about bending

    I'm building a singlespeed mtb, using an old diamondback frame with horizontal dropouts and 132mm rear spacing. I'm just using the 7-speed cassette hub that came with the bike, and using a cog with spacers mounted on the freehub body.

    I removed a couple of spacers from the drive-side axle and stuck them on the non-drive-side axle, since the cassette lockring will be able to nearly touch the frame and I don't need to worry about the chain since the cog will be near the middle of the freehub body.
    This allows me to have minimal dish in the rear wheel.

    My worry now: is there too much exposed axle (i.e., distance between the bearings and the dropout) on the non-drive-side? This wouldn't be a worry for road riding, but more exposed axle on the non-drive-side could be a problem for off-road riding with lots of bumps, causing the axle to eventually bend and then need to be replaced.

    So I'm asking a question about optimization between two factors:
    1) I would like the rear wheel to be as close to dishless as possible - equal spoke tension, stronger wheel, more likely to last a really long time without breaking spokes or coming out of true. I accomplish this by switching spacers from the drive-side to non-drive-side axle (so effectively moving the hub body over with respect to the rim) and then re-dishing the rim.
    2) The further over I move the hub body (and it's not as if I can do it all that far; this is limited by the cassette lockring hitting the inside of the dropouts), the more spacers there are on the non-drive-side axle. This means increased distance between the non-drive-side bearings and the left rear dropout, and as this length grows, the bending moment on that section of axle increases. Too much bending moment, and your axle ends up bending, and will eventually need to be replaced. This is the reason freehubs are superior to freewheel hubs on multi-speed bikes, because freewheel hubs leave a long distance of exposed axle between the drive-side bearings and the right dropout (and it's extra-problematic on the drive-side, because there it's dealing with horizontal force from the pulling of the chain on the sprockets, along with vertical force from rider's weight and hitting bumps).

    I suspect that with 36 spokes the wheel is already plenty strong without having re-spaced anything, and it'd be prudent to move a spacer back over to the drive-side. But I'm really not sure.
    Does it look like too much exposed axle on the non-drive-side?




  2. #2
    cab horn
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    Tim - that looks fine with the amount of space on the NDS. You should see how much space is on my fixed gear to make the chainline work properly. Of course I only weigh 120lbs.

    Also, why can't you move the spacer from NDS over back to the DS? You can just move the cog closer to the dropout with your SS conversion kit can't you?
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

  3. #3
    Senior Member robo's Avatar
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    I was just thinking that before the days of cassette hubs, weren't the drive side bearings always quite a ways in?

  4. #4
    biked well well biked's Avatar
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    I think you'd be better off having less exposed axle on the non-drive side. It's kind of a question of one advantage leading to a disadvantage elsewhere, but my experience has been that 26" wheels with 36 spokes on something like those old Araya mtb rims (if that's what you have there) are plenty durable as is, don't come out of true often, and will not be a problem for breaking spokes as long as the wheel is built properly. I've done a bunch of off-road riding on wheels just like that, they're a very robust wheel-

    P.S.: I weighed about 175 back in the days of 7 speed mtb's, when I rode wheels like that-
    Last edited by well biked; 03-29-07 at 08:53 AM.

  5. #5
    me have long head tube TallRider's Avatar
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    I weight 180# and am 6'5" so need to worry more about wheelbuild strength and axle bending. Hence the optimization question.

    operator: I can move spacers back over to the drive-side and still get proper chainline. The reason for minimizing spacers on the drive-side would be to have a less-dished wheel.

    well biked: I do have those old wide-ish, single-wall Araya mtb rims. I think you're probably right about wheelbuild strength being plenty - I'll move at least the 1mm spacer back over from the non-drive-side to the drive-side.

  6. #6
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    I don't think you have a problem. I have a '93 Trek 7000 MTB that came with a 7-speed Deore LX drivetrain but was spaced 135 mm. The NDS side of the rear hub had at least as many spacers as yours does and it was never a problem even using it on some pretty rough W Va. trails.

    Modern axles are pretty high strength steel so they take a lot more to bend and/or break than their predecessors.

  7. #7
    cab horn
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    Quote Originally Posted by timcupery
    operator: I can move spacers back over to the drive-side and still get proper chainline. The reason for minimizing spacers on the drive-side would be to have a less-dished wheel.
    Ahh roger that, I need to learn how to read
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

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