brake mods to change from 26" to 24" wheel?

Discussion in 'Cycling Equipment' started by jtaylor, Jan 20, 2006.

  1. jtaylor

    jtaylor Guest

    "bob mcree" <[email protected]> wrote in message
    news:[email protected]
    > Hi, for reasons of getting higher RPM for better performance of my hub
    > motor, i'm considering changing the front wheel on my old TREK 950 from
    > the stock 26" to 24". Can I get center pull brakes that will attach to
    > the stock braze-ons with longer arms for the smaller wheel? thanks...
    > -bob


    There are several different '24"' rim and tyre sizes - almost as many as
    there are '26"' sizes.

    Best thing is to borrow a set of the longest brakes your local (real) bike
    shop has, and try whatever 24" size you are considering. That'll give you
    an idea of

    a) if it will; and

    b) what length of brake will be required to make it

    work.
     
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  2. bob mcree

    bob mcree Guest

    Hi, for reasons of getting higher RPM for better performance of my hub
    motor, i'm considering changing the front wheel on my old TREK 950 from
    the stock 26" to 24". Can I get center pull brakes that will attach to
    the stock braze-ons with longer arms for the smaller wheel? thanks...
    -bob
     
  3. pool screen house supply, aluminum supply, a contractors hardware
    warehouse ect.
    may have scrap aluminum plate-1/8-3/16" x 1 1/2 or more.
    bolt to-shape for tire-drill and rebolt brake assemblies
     
  4. Chalo

    Chalo Guest

    bob mcree wrote:
    >
    > Hi, for reasons of getting higher RPM for better performance of my hub
    > motor, i'm considering changing the front wheel on my old TREK 950 from
    > the stock 26" to 24". Can I get center pull brakes that will attach to
    > the stock braze-ons with longer arms for the smaller wheel?


    No. There are some wheel size swaps that can be forced to work, but
    that's not one of them. Put a 24" wheel on a 26" fork, and the brake
    bosses will be directly alongside the rim. Not only do they prevent
    the use of linear-pull or cantilever brakes, but they would get in the
    way of a caliper brake if you opted to finagle something along those
    lines.

    There is some possibility that you could mount a cantilever stud
    adapter plate on the *back* side of the fork, but you'd probably need
    something like a drop bolt to mount it in the right location.
    http://www.danscomp.com/cgi-bin/hazel.cgi?action=DETAIL&item=489051

    A 700c fork with cantilever bosses can sometimes be pressed into use
    with a U-brake or rollercam brake on a 24" wheel. However, U-brake
    studs are 9mm in diameter while canti studs are 8mm in diameter, so
    you'd have to get both a compatible hybrid fork and a pair of precisely
    made sleeves to fatten up the 8mm bosses to 9mm. The good thing about
    doing this is that the fork would add back the 1" of front end height
    you'd lose by using a 24" wheel.

    You could probably just increase the voltage of your hub motor drive by
    12V, which would substantially increase your wheel RPM.

    What kind of hub motor are you using?

    Chalo Colina
     
  5. bob mcree

    bob mcree Guest

    thanks for all the mechanical info..

    >
    > You could probably just increase the voltage of your hub motor drive by
    > 12V, which would substantially increase your wheel RPM.

    actually higher voltage won't buy me anything because i can't get going
    fast enough for the motor to run in its 20 mph high efficiency range
    with the 32A I'm giving it now, and i can't give it any more current for
    speed control / battery reasons. higher voltage will let you go faster
    but only if you have enough power to get up to that speed in the first
    place.
    >
    > What kind of hub motor are you using?
    >

    I'm using the Wilderness Energy 600W brushed motor, it really draws over
    1000w at 36v. going to 48V would add way too much cost and weight and
    would not as it turns out give me any more range, just a higher
    theoretical top speed.
    > Chalo Colina
    >
     
  6. Chalo

    Chalo Guest

    bob mcree wrote:
    > .
    > actually higher voltage won't buy me anything because i can't get going
    > fast enough for the motor to run in its 20 mph high efficiency range
    > with the 32A I'm giving it now, and i can't give it any more current for
    > speed control / battery reasons. higher voltage will let you go faster
    > but only if you have enough power to get up to that speed in the first
    > place.


    I see.

    I put that same motor on my sweetie's electric bike, which also has 26"
    wheels. I set it up with a Curtis 1505 controller, good for 24V and a
    maximum of 80A. I've measured the peak amperage at 60A. That gives
    her a useful amount of torque, but a modest top speed.

    Chalo Colina
     
  7. bob mcree

    bob mcree Guest

    Chalo wrote:
    > bob mcree wrote:
    >
    >>.
    >>actually higher voltage won't buy me anything because i can't get going
    >>fast enough for the motor to run in its 20 mph high efficiency range
    >>with the 32A I'm giving it now, and i can't give it any more current for
    >>speed control / battery reasons. higher voltage will let you go faster
    >>but only if you have enough power to get up to that speed in the first
    >>place.

    >
    >
    > I see.
    >
    > I put that same motor on my sweetie's electric bike, which also has 26"
    > wheels. I set it up with a Curtis 1505 controller, good for 24V and a
    > maximum of 80A. I've measured the peak amperage at 60A. That gives
    > her a useful amount of torque, but a modest top speed.
    >
    > Chalo Colina
    >


    there's an interesting phenomenon that has been empirically shown to be
    true in general; that increasing the voltage on an ebike will give you a
    faster top speed but will not increase your range. this seems
    counter-intuitive but it has been demonstrated to be true time after
    time. i could increase my battery weight from 30 to 40 pounds to go from
    36V to 48V but all that extra battery wouldn't let me go any further,
    just faster. if i can't get going 25 mph or so because of hills, the
    extra battery would buy me almost nothing. -bob
     
  8. Chalo

    Chalo Guest

    bob mcree wrote:
    > i could increase my battery weight from 30 to 40 pounds to go from
    > 36V to 48V but all that extra battery wouldn't let me go any further,
    > just faster. if i can't get going 25 mph or so because of hills, the
    > extra battery would buy me almost nothing.


    Speaking of almost nothing: I think that's what you will get for your
    trouble if you switch from a 26" wheel to a 24" wheel. You will need a
    bigger change in wheel diameter to get a significant improvement in
    efficiency and mechanical advantage. Consider switching to a 20" wheel
    if possible. That would require a different fork yet, preferably an
    adjustable fork, so that the bike's ride height and angles would not be
    adversely affected. Such forks exist:

    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7213032224
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7212017482

    Something like this would allow you to use pretty much any wheel size
    you chose. Mounting a front brake would be another matter.

    Chalo Colina
     
  9. time to graph the alternatives- a 20" wheel reduces speed as the motor
    revs up to the desir4ed speed range
    sounds like NASA work.
     
  10. bob mcree

    bob mcree Guest

    Chalo wrote:
    > bob mcree wrote:
    >
    >>i could increase my battery weight from 30 to 40 pounds to go from
    >>36V to 48V but all that extra battery wouldn't let me go any further,
    >>just faster. if i can't get going 25 mph or so because of hills, the
    >>extra battery would buy me almost nothing.

    >
    >
    > Speaking of almost nothing: I think that's what you will get for your
    > trouble if you switch from a 26" wheel to a 24" wheel. You will need a
    > bigger change in wheel diameter to get a significant improvement in
    > efficiency and mechanical advantage.


    you're right of course. the 26 to 24 switch will only increase RPM by
    less than 10%. that might be enough to make a difference but it might be
    a lot of work for not much gain. i just didn't imagine putting a smaller
    wheel on. a 20" would increase by almost 25% and that would be
    significant. it would lower my top speed by 25% too, and that might be a
    real problem. that would take me down to 15 mph or so max motor assisted
    speed.

    I'll look into the forks you mentioned.

    > Something like this would allow you to use pretty much any wheel size
    > you chose. Mounting a front brake would be another matter.


    well, i need a front brake... using the motor for braking just isn't
    good enough.
    >
    > Chalo Colina
    >
     
  11. Nate Knutson

    Nate Knutson Guest

    bob mcree wrote:
    > Chalo wrote:
    > > bob mcree wrote:
    > >
    > >>i could increase my battery weight from 30 to 40 pounds to go from
    > >>36V to 48V but all that extra battery wouldn't let me go any further,
    > >>just faster. if i can't get going 25 mph or so because of hills, the
    > >>extra battery would buy me almost nothing.

    > >
    > >
    > > Speaking of almost nothing: I think that's what you will get for your
    > > trouble if you switch from a 26" wheel to a 24" wheel. You will need a
    > > bigger change in wheel diameter to get a significant improvement in
    > > efficiency and mechanical advantage.

    >
    > you're right of course. the 26 to 24 switch will only increase RPM by
    > less than 10%. that might be enough to make a difference but it might be
    > a lot of work for not much gain. i just didn't imagine putting a smaller
    > wheel on. a 20" would increase by almost 25% and that would be
    > significant. it would lower my top speed by 25% too, and that might be a
    > real problem. that would take me down to 15 mph or so max motor assisted
    > speed.
    >
    > I'll look into the forks you mentioned.
    >
    > > Something like this would allow you to use pretty much any wheel size
    > > you chose. Mounting a front brake would be another matter.

    >
    > well, i need a front brake... using the motor for braking just isn't
    > good enough.


    The 20" wheel thing might also work with a new fork with disc tabs
    that's either 29'erish, suspension corrected, or a suspension fork.
    Then you could run a front disc brake. I haven't thought about it much
    but you could probably get the geometry in the right ballpark with the
    right 20" size and tire size, as there's a lot of room between 406's
    with the smallest tires you can get for them and 451's with the
    largest. I'm not sure how the rake and trail on this would work out.
    Also don't know what kind of headtube and headset your bike has, but if
    it's 1" threaded then this will be a pain.
     
  12. Sorni

    Sorni Guest

    [email protected] wrote:

    > do one metric, one...


    so, like, one and change in american?
     
  13. Chalo

    Chalo Guest

    bob mcree wrote:
    >
    > i just didn't imagine putting a smaller
    > wheel on. a 20" would increase by almost 25% and that would be
    > significant. it would lower my top speed by 25% too, and that might be a
    > real problem. that would take me down to 15 mph or so max motor assisted
    > speed.


    Remember you'll have more thrust available; that will allow the motor
    to spin up to a higher RPM and your top speed may not fall much.

    > I'll look into the forks you mentioned.
    >
    > > Something like this would allow you to use pretty much any wheel size
    > > you chose. Mounting a front brake would be another matter.

    >
    > well, i need a front brake... using the motor for braking just isn't
    > good enough.


    If you have an unusually good bike shop in your area, you could have
    cantilever studs brazed onto a fork like that. If you are on friendly
    terms with a machinist, you could persuade him to make you a clamp-on
    fork bridge that you could use to mount a caliper brake, which you
    could slide up or down to get a perfect fit with whatever wheel.

    Chalo Colina
     
  14. bob mcree

    bob mcree Guest

    > If you have an unusually good bike shop in your area, you could have
    > cantilever studs brazed onto a fork like that.


    thanks for the advice. a disc brake is impossible because the hub motor
    takes up all the space between the forks. i am going to ask my welder
    friend about putting on some different mounts...

    -bob
     
  15. A Muzi

    A Muzi Guest

    bob mcree wrote:
    > Hi, for reasons of getting higher RPM for better performance of my hub
    > motor, i'm considering changing the front wheel on my old TREK 950 from
    > the stock 26" to 24". Can I get center pull brakes that will attach to
    > the stock braze-ons with longer arms for the smaller wheel? thanks...


    Probably not but you can certainly move the brazed on brake
    posts to the proper location.

    --
    Andrew Muzi
    www.yellowjersey.org
    Open every day since 1 April, 1971
     
  16. Dave

    Dave Guest

    On Sat, 21 Jan 2006 04:15:19 GMT, bob mcree <[email protected]>
    wrote:

    >> bob mcree wrote:

    >there's an interesting phenomenon that has been empirically shown to be
    >true in general; that increasing the voltage on an ebike will give you a
    >faster top speed but will not increase your range. this seems
    >counter-intuitive but it has been demonstrated to be true time after
    >time. i could increase my battery weight from 30 to 40 pounds to go from
    >36V to 48V but all that extra battery wouldn't let me go any further,
    >just faster. if i can't get going 25 mph or so because of hills, the
    >extra battery would buy me almost nothing. -bob



    I could be wrong, but it seems to me that range on an ebike will be
    proportional to battery capacity (Amp-hour rating) while top speed
    will be proportional to voltage. This is for a similar current draw
    at each voltage, of course, which may not be a very good assumption.

    Does this fit with your experience?
     
  17. bob mcree

    bob mcree Guest

    Dave wrote:
    > On Sat, 21 Jan 2006 04:15:19 GMT, bob mcree <[email protected]>
    > wrote:
    >
    >
    >>>bob mcree wrote:

    >>
    >>there's an interesting phenomenon that has been empirically shown to be
    >>true in general; that increasing the voltage on an ebike will give you a
    >>faster top speed but will not increase your range. this seems
    >>counter-intuitive but it has been demonstrated to be true time after
    >>time. i could increase my battery weight from 30 to 40 pounds to go from
    >>36V to 48V but all that extra battery wouldn't let me go any further,
    >>just faster. if i can't get going 25 mph or so because of hills, the
    >>extra battery would buy me almost nothing. -bob

    >
    >
    >
    > I could be wrong, but it seems to me that range on an ebike will be
    > proportional to battery capacity (Amp-hour rating) while top speed
    > will be proportional to voltage. This is for a similar current draw
    > at each voltage, of course, which may not be a very good assumption.
    >
    > Does this fit with your experience?
    >
    >

    every motor has an RPM at which it runs most efficiently. the motor may
    not have enough power to reach that RPM if the gearing is too high.
    reducing the wheel diameter would let my motor run at a speed where
    it runs more efficiently. yes more voltage gives you more speed but
    different motors run most efficiently at different speeds depending
    on the gearing/wheel diameter.

    -bob
     
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