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  1. #1
    s-o
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    Running a dynohub backwards?

    I'm building up a Cotic Roadrat as my winter bike, and plan to run it with disc brakes.
    The problem is that I want to use a dynohub up front, and since the Roadrat fork has the disc brake mount positioned on the front of the right fork leg, the dynohub (an Alfine S501) will have to run against the recommended rotational direction.
    Is this going to be a problem? Will the hub loosen itself, or will it tighten the bearings while running? Come to think of it, why does a dynohub have a recommended rotational direction in the first place? It's AC, so it should be quite agnostic about directions

    /s-o

  2. #2
    Gears? CliftonGK1's Avatar
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    If the Alfine is similar to the SON28 in general construction, then don't do it. The core of the hub can come unscrewed from the hub shell.
    "I feel like my world was classier before I found cyclocross."
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    Seņor Member USAZorro's Avatar
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    Not to mention it will work in reverse, sucking in light until the energy level becomes critical and it explodes.

    For a straight answer, probably would be best to contact the manufacturer, no?
    The search for inner peace continues...

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    Quote Originally Posted by USAZorro View Post
    Not to mention it will work in reverse, sucking in light until the energy level becomes critical and it explodes.

    For a straight answer, probably would be best to contact the manufacturer, no?
    Don't you watch Star Trek? Detonating your warp core is always the best solution if you need that last little bit of speed.
    1988 Miele Azsora

  5. #5
    Gears? CliftonGK1's Avatar
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    Quote Originally Posted by USAZorro View Post
    Not to mention it will work in reverse, sucking in light until the energy level becomes critical and it explodes.
    Wouldn't that eventually turn the headlight into a singularity and collapse space around it forming a black hole?

    s-o, you don't want to be responsible for destroying the entire solar system, do you?
    "I feel like my world was classier before I found cyclocross."
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    The only generator hub I know of that can be run in either direction is the SON 20R. Costs a little bit more but it may be worth it in your case.

  7. #7
    Reeks of aged cotton duck Hydrated's Avatar
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    Quote Originally Posted by USAZorro View Post
    Not to mention it will work in reverse, sucking in light until the energy level becomes critical and it explodes.


    I wanted to say that...
    "We sleep safe in our beds because rough men stand ready in the night to visit violence on those who would do us harm." George Orwell

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    Quote Originally Posted by s-o View Post
    Come to think of it, why does a dynohub have a recommended rotational direction in the first place? It's AC, so it should be quite agnostic about directions
    AC? Really?

  9. #9
    s-o
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    Quote Originally Posted by CliftonGK1 View Post
    If the Alfine is similar to the SON28 in general construction, then don't do it. The core of the hub can come unscrewed from the hub shell.
    That sounds like a really good reason not to.
    The best solution might be to buy a fork with a more conventional placement of the brake.


    Quote Originally Posted by USAZorro View Post
    Not to mention it will work in reverse, sucking in light until the energy level becomes critical and it explodes.
    That sounds unlikely. On the other hand, on a really bright day, I just might have the fastest reversing bike in the universe :-)


    Quote Originally Posted by USAZorro View Post
    For a straight answer, probably would be best to contact the manufacturer, no?
    I've tried that, but Shimano Europe seems to have better things to do than answering their mail ...


    Quote Originally Posted by CliftonGK1 View Post
    Wouldn't that eventually turn the headlight into a singularity and collapse space around it forming a black hole?

    s-o, you don't want to be responsible for destroying the entire solar system, do you?
    Of course not. That's CERN:s responsibility, so they will probably sue me for copyright violation if I did that :-p


    Quote Originally Posted by njkayaker View Post
    AC? Really?
    Really.
    (I know that Wikipedia isn't considered the most reliable source, but since most led light drivers for dynohubs have a bridge rectifier built in, wikipedia just might have a point there :-)
    Last edited by s-o; 09-02-09 at 05:52 AM. Reason: correcting typos, cat on keyboard

  10. #10
    Primate Metzinger's Avatar
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    Solution: don't run disc brakes in the winter. They're a bad choice unless you're commuting down Mount Doom everyday.
    Use a generator hub with a roller brake. Winter is what those things are designed for.
    Disc brakes look cool but aren't a good idea here.

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    Quote Originally Posted by s-o View Post
    Really.
    (I know that Wikipedia isn't considered the most reliable source, but since most led light drivers for dynohubs have a bridge rectifier built in, wikipedia just might have a point there :-)
    No reason wikipedia isn't a reasonable source for this. ("Dynamo" is a silly word for them!)

  12. #12
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    It won't matter on the alfine or any of shimano's dynohubs, they are all AC output, so the direction of rotation does not matter. And on the two shimano models I own, there is no mechanical reason not to either. I think the arrow is just to keep the output terminals on the 'standard' side of the hub. It lets the wheel builder know which way to align the rim, they have their own 'standard' way they like to do it also. Ditto for the person who fixes and remounts your tire, if it isn't you.
    Last edited by tspoon; 09-04-09 at 01:09 PM.

  13. #13
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    Quote Originally Posted by tspoon View Post
    It won't matter on the alfine or any of shimano's dynohubs, they are all AC output, so the direction of rotation does not matter. And on the two shimano models I own, there is no mechanical reason not to either. I think the arrow is just to keep the output terminals on the 'standard' side of the hub. It lets the wheel builder know which way to align the rim, they have their own 'standard' way they like to do it also. Ditto for the person who fixes and remounts your tire, if it isn't you.
    Here's a quote from Peter White regarding the SON Dynohub:

    If the hub is used backwards, the central core of the hub can unscrew from the outer shell. This can cause the hub to lock up, and it can easily damage the threads, making it impossible to reinstall the hub core. You'll be left stranded on the side of the road. This alignment is just as important as your pedal threads, which are right handed on the right pedal, and left handed on the left pedal. These threadings are different because if you had a right hand thread on your left pedal, the pedal could unthread from the crank. For exactly the same reason, the SON hub must be used with the connectors on the right side of the bike, the same side as your derailleurs and chain.
    Don't run the hub backwards unless you get confirmation that it will work from Shimano. Unless of course you like having your hub randomly fail after 100-1000 miles.

    Personally, I'd recommend running battery lights, using a fork that has the disc calipers on the correct side, or ditching the front disc brake for v-brakes. If you use a v-brake in the front you can still run disc in the back. Icy nasty weather is one of the few times where your rear brake becomes more important than the front so it seems like it could be a good compromise.

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