Why don't hubs get hot?

Discussion in 'Cycling Equipment' started by Jeff, May 9, 2003.

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  1. Jeff

    Jeff Guest

    I just made my local climb and descent - 6 miles uphill, then 6 miles downhill, 20-40 mph. Ambient
    temp is 75 degrees F.

    I would expect some heat, but the hubs are cold.

    Are ball bearings so smooth? Does my hub dissipate heat so efficiently?
     
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  2. B. Sanders

    B. Sanders Guest

    "Jeff" <[email protected]> wrote in message news:[email protected]...
    > I just made my local climb and descent - 6 miles uphill, then 6 miles downhill, 20-40 mph. Ambient
    > temp is 75 degrees F.
    >
    > I would expect some heat, but the hubs are cold.
    >
    > Are ball bearings so smooth? Does my hub dissipate heat so efficiently?

    Yes, and yes. Your chain-driven bike drive train is ~98% efficient. The wheel bearings have
    extremely low friction. That means no wasted energy heating up your components - it all gets
    transmitted to the road/trail pushing you forward.

    Brakes will get hot, however. Rim brakes can heat up a rim so much (on tandems) that they'll
    actually melt the innertube. I haven't heard of this happening on a solo bike.

    -Barry
     
  3. Doug

    Doug Guest

    >I just made my local climb and descent - 6 miles uphill, then 6 miles downhill, 20-40 mph. Ambient
    >temp is 75 degrees F.
    >
    >I would expect some heat, but the hubs are cold.
    >
    >Are ball bearings so smooth? Does my hub dissipate heat so efficiently?

    The miracle of bearings really. Consider some applications where thousands or tens of thousands of
    pounds rest on those little puppies. Or to be more precise, are spread across many of them with some
    grease in there to keep things kosher. Bearings in general are incredible marvels of machining
    tolerances that we take for granted.
     
  4. I've seen rim brakes result in an exploding tube on a long downhill - solo not tandem It was pretty
    extreme downhill however

    hubs now do get hot - but that's because of the heat imparted by disc brakes..

    "B. Sanders" <[email protected]> wrote in message news:[email protected]... "Jeff"
    <[email protected]> wrote in message news:[email protected]...
    > I just made my local climb and descent - 6 miles uphill, then 6 miles downhill, 20-40 mph. Ambient
    > temp is 75 degrees F.
    >
    > I would expect some heat, but the hubs are cold.
    >
    > Are ball bearings so smooth? Does my hub dissipate heat so efficiently?

    Yes, and yes. Your chain-driven bike drive train is ~98% efficient. The wheel bearings have
    extremely low friction. That means no wasted energy heating up your components - it all gets
    transmitted to the road/trail pushing you forward.

    Brakes will get hot, however. Rim brakes can heat up a rim so much (on tandems) that they'll
    actually melt the innertube. I haven't heard of this happening on a solo bike.

    -Barry
     
  5. Ball bearings don't get that hot. Not at the speed a bicycle's hub is turning, any way.

    May you have the wind at your back. And a really low gear for the hills! Chris

    Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner
     
  6. Superslinky

    Superslinky Guest

    Jeff said...

    > I just made my local climb and descent - 6 miles uphill, then 6 miles downhill, 20-40 mph. Ambient
    > temp is 75 degrees F.
    >
    > I would expect some heat, but the hubs are cold.
    >
    > Are ball bearings so smooth? Does my hub dissipate heat so efficiently?

    It's because there aren't that many RPMs. At 40mph, you are only turning about 470 RPM.
     
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