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  1. #1
    Terry Porritt
    Guest

    Default Completely O/T.. Car wheel frictional power loss

    This is for all you car buffs.
    I notice that wheel trims and mag type wheels have either purely radial "spokes", or forward facing, or rearward facing, relative to clockwise rotation.

    Now it is relatively trivial to calculate the frictional power dissipated by a plain disc rotating in a fluid (of infinite extent) and there is from memory of turbine days, lots of published data for discs and turbine wheels, going back to the ark.

    But what about car wheels, and is it better to have forward facing or rearward facing spoke shapes, or is there no discernible difference?

    Base your calculations on a 14" wheel, and a linear road speed of 100km/hour. Home work to be handed in by 2.30 pm tomorrow.

    Thank you.

  2. #2
    Graham L
    Guest

    Default Re: Completely O/T.. Car wheel frictional power loss

    I suspect it's difficult.

    I know cycle racers use solid disks to avoid the drag of spokes.

    I read the autobiography of a guy who went to work for Rolls-Royce, and found that no-one had ever worked out the mathematics of the superchargers for Merlin engines. By the time he had finished, the Merlin was producing well over 2000 HP, from just over 1000 with the original supercharger which "worked".

    I remember from somewhere that the vanes on "snail" blowers work differently when sloped forward and backwards.. Forward gives more output, backwards is self-limiting (which helps to avoid motors burning
    out).

    14" and km/h ... Do the working in furlongs/fortnight to make the numbers easier.

  3. #3
    Terry Porritt
    Guest

    Default Re: Completely O/T.. Car wheel frictional power loss

    Better still Graham, versts/hour.

  4. #4
    godfather
    Guest

    Default Re: Completely O/T.. Car wheel frictional power loss

    Terry, please advise the wind allowance, its velocity (in leagues per decade?) and its direction relative to car motion.

    And my car wheels have wire spokes (about 48 of them in each wheel).

  5. #5
    -=JM=-
    Guest

    Default Re: Completely O/T.. Car wheel frictional power loss

    I'm picking that you've been rather bored lately or something Terry. I think you should send that one in to New Scientist. There are always weird and wonderful questions in there that people manage to answer.

  6. #6
    Terry Porritt
    Guest

    Default Re: Completely O/T.. Car wheel frictional power loss

    The very opposite of bored JM, I think it is the effect of some medication Im on, there is a rosy glow around the place these days, and all's right with the world

    Seriously, Goddie, I am hoping someone may know of any published data/measurements on wheels. It is just possible that the benefits of spoilers and other add-on go faster goodies,etc, may be negated by high windage loss wheels that are designed only to look good. The information must be out there somewhere.

  7. #7
    Graham L
    Guest

    Default Re: Completely O/T.. Car wheel frictional power loss

    It's the painted stripe that makes it faster. The best and cheapest tuning hint is to weaken the spring on the accelerator.

  8. #8
    E.ric
    Guest

    Default Re: Completely O/T.. Car wheel frictional power loss

    Did I read this question right?

    It depends on weather you put the wheels on the driver side of the car or the passengers side.

  9. #9
    Terry Porritt
    Guest

    Default Re: Completely O/T.. Car wheel frictional power loss

    Well Eric, the question really was whether forward facing spokes(spokes, for want of a better word) pump more air than rear facing spokes,and hence consume more power. If so how much power, and how much more that a plain surfaced wheel trim.

    The question of which side I hadnt considered, because that can always be taken care of with handed wheel trims/wheels.

    Cheers

  10. #10
    E.ric
    Guest

    Default Re: Completely O/T.. Car wheel frictional power loss

    It was when I saw "relative to clockwise rotation." in your first posting, I thought it was a trick question, as driver side the wheels would rotate in clockwise direction and passenger side would rotate anti-clockwise.

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