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  1. #1
    Cranky Old Bastard
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    Experience with OC rims?

    Anyone have experience with Off-Center rims?

    For those that don't know; OC rims have the spoke holes drilled off center (usually 4mm) for use with an off-center hub (like any normal rear). The rim will still be centered while the offset allows spoke lengths to be closer to the same on both sides.

    The science is interesting and makes sense: more even spoke tension on both sides of the wheel. Should make the wheel stronger, stay true longer??? Does the theory actually work in practice?

    On the disc rear hub I've picked out the spokes are offset 3.5mm from center. The rims are 4mm offset, so the spokes may be exactly the same length both sides, does that mean the tension could be exactly the same also? If so, I would think that would make a perfect wheel, like a normal front.

    It is ironic that with disc hubs the front has more offset than the rear and can't be quite as perfect. But the OC rim still allows the spokes to be closer to the same length.

    I was looking at Velocity Aerohead OC rims but it seems they've been discontinued and replaced with the A23 OC.
    I'd picked out some standard Kinlins and wonder if the A23 OCs would be worth twice the money?

    TIA
    Last edited by Randy99CL; 04-18-2013 at 08:57 AM.

  2. #2
    RoadBikeReview Member
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    My old Dura Ace wheels (from 2008 or so) have off center rims. They have been great and always stay true despite hard riding on bad roads but I have no idea if the OC rims have anything to do with that. I suspect the OC might have something to do with their ability to make the wheels so strong with only 20 spokes in the rear but I canít say for sure itís a factor. Donít know.

  3. #3
    Online Wheel Builder
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    First off, an OC rim will not make a wheel stay true longer. Build quality, tension equality, and proper stress relief will be the real determinants of how durable a wheel is.

    I only have experience with one OC rim though, which is the A23 OC from Velocity. I have built them up to the White Industries T11 rear, and the Tune Mag 170. And I was really impressed with how high the tension was on the NDS. I'm not sure it makes much of a real world difference in rigidity, but it's definitely noticeable when tensioning in the stand.

  4. #4
    Cranky Old Bastard
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    Thanks for the replies guys!

    The way I see it, the uneven spoke tension has got to be the biggest problem with a rear wheel. The two hub flanges are stressed differently and the rim is stressed unevenly depending on which flange the spoke came from.

    I'm dealing with disc hubs, so the rim gets uneven stress (would it be a twisting motion?) when I pedal and the opposite uneven stress when I brake. The spokes stretch differently depending on whether I'm pedaling or braking.

    I'm new at this; does a disc (especially road) rear wheel have more problems with breaking spokes and rims? I would expect it would.

    I've convinced myself to spend the extra and get the A23 OCs; I just can't ignore the physics. As I explained above, in this case the tension should be very close to equal on all the spokes.

    And I've read so many good things about the 23mm wide(r) rims.

  5. #5
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    Quote Originally Posted by Zen Cyclery View Post
    First off, an OC rim will not make a wheel stay true longer. Build quality, tension equality, and proper stress relief will be the real determinants of how durable a wheel is.
    Sorry not following you here. A properly assembled OC rim better balances DS & NDS tension which equals a wheel that stays true longer.

    OC RIM = better tension equality
    Last edited by farva; 04-24-2013 at 08:54 PM.

  6. #6
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    Quote Originally Posted by Randy99CL View Post

    I'm new at this; does a disc (especially road) rear wheel have more problems with breaking spokes and rims? I would expect it would.
    Shouldn't be a problem provided radial lacing is not used. Radial laced wheels do not handle torque loads as well as cross laced rims

  7. #7
    Cranky Old Bastard
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    Quote Originally Posted by Randy99CL View Post
    On the disc rear hub I've picked out the spokes are offset 3.5mm from center. The rims are 4mm offset, so the spokes may be exactly the same length both sides, does that mean the tension could be exactly the same also? If so, I would think that would make a perfect wheel, like a normal front.

    It is ironic that with disc hubs the front has more offset than the rear and can't be quite as perfect. But the OC rim still allows the spokes to be closer to the same length.
    So I'm ordering the parts to build these wheels.

    Put the numbers into a spoke calculator and the rear are only 0.1mm different: 289.8 NDS, 289.9 DS. It does look like the rear will have equal tension on both sides.

    The front are not as close: 290.4 and 291.1 but still closer than with a normal rim.

    Question for wheelbuilders: Isn't it better to buy spokes a little long instead of too short? With alloy nips I'd guess that the spokes should go through the head of the nipple for support; if the spoke was short of the head I can imagine it would be easier for it (the nipple) to break off at the rim. Or am I overthinking it?

    The spokes are available in 2mm, odd increments. I'm thinking of just ordering all 291mm to make it easier.

  8. #8
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    That will probably work. If the spokes are too long you risk bottoming out the nipple before you get the desired tension but you are not anywhere near that.
    I would use brass nipples, there is no reason to use aluminum.

    Quote Originally Posted by Randy99CL View Post
    So I'm ordering the parts to build these wheels.

    Put the numbers into a spoke calculator and the rear are only 0.1mm different: 289.8 NDS, 289.9 DS. It does look like the rear will have equal tension on both sides.

    The front are not as close: 290.4 and 291.1 but still closer than with a normal rim.

    Question for wheelbuilders: Isn't it better to buy spokes a little long instead of too short? With alloy nips I'd guess that the spokes should go through the head of the nipple for support; if the spoke was short of the head I can imagine it would be easier for it (the nipple) to break off at the rim. Or am I overthinking it?

    The spokes are available in 2mm, odd increments. I'm thinking of just ordering all 291mm to make it easier.

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