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The great SFPM Debate

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  • rides20
    replied
    Re: The great SFPM Debate

    ..the buffer might have to wait!..I just bought 2 RD350 frames...one for me and one to build for a friend of mine! sorry for going off topic, but I'm excited!

    Leave a comment:


  • fly
    replied
    Re: The great SFPM Debate

    Why didn't you just say so in the begining.

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  • rides20
    replied
    Re: The great SFPM Debate

    ..Cool...Now I think It's time for me to get a bigger buffer!

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  • mcaswell
    replied
    Re: The great SFPM Debate

    Look at it like this

    The CIRCUMFERENCE of a wheel is Diameter (D) x Pi (3.14)
    Or roughly D x 3

    So, a 4" wheel = 4 x 3 = 12.
    One revolution of that wheel will travel 12" along the ground

    A 6" wheel = 6 x 3 = 18
    One revolution of that wheel will travel 18" along the ground

    An 8" wheel = 8 x 3 = 24
    One revolution of that wheel will travel 24" along the ground

    If these wheels are mounted on your buffer, which does 1 revolution, a point on the circumference of will travel different distances, depending on the diameter of the wheel.

    If the motor revolves the wheel 3500 RPM - then the distance of that point on each wheel will travel further as the wheels get bigger.

    So, seeing as RPM is a time element, greater distances will be traveled in the given time of one minute.

    Clear as mud eh??

    Leave a comment:


  • fxstcguy98
    replied
    Re: The great SFPM Debate

    My turn, think of tying a rock at the end of a 10' string, if you held the string at arms length and spun in a circle the rock will be hauling balls to keep up with your hand.

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  • mpierich
    replied
    Re: The great SFPM Debate

    Originally posted by rides20
    ..Alright everyone bear with me here...
    Think of it this way...say a 6" wheel and an 8" wheel are traveling at the same RPM's. The circumference around the 8" is more inches than the circumference around the 6". That means that the surface of the 8" has to travel _more_inches _in_the_same_time_period_ than the surface of the 6", which equates to more feet per minute, or inches per second, or miles per hour even.

    I figger when a piece grabs on the wheel and leaves my hand (which happens a lot less frequently nowadays), it's traveling at about 80 mph.

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  • rides20
    replied
    Re: The great SFPM Debate

    HAHAHAHAHAH....I think i'll just stick to polishing! I guess I dont need to know why I can make stuff shine!HAHAAHH..Actually sswee, that was a big help it is actually a tad clearer now. Thanks (I clicked your add reputation button) HAHAHAHAAHAHAH

    Leave a comment:


  • sswee
    replied
    Re: The great SFPM Debate

    I was talking to rides20. Try the flash chat.

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  • pickleboy
    replied
    Re: The great SFPM Debate

    were you talking to me or him on this?

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  • sswee
    replied
    Re: The great SFPM Debate

    No, a motor turning 3000 RPM will turn 3000 RPM no matter what size wheel is on it. The larger the wheel the higher the SFPM.

    If you put a larger wheel on a motor and it turns slower than with a smaller wheel on the same motor.
    1. the wheel is too large for the motor. (a Chevy 350 in a Kenworth)
    2. the motor is weak and fixing to burn up.
    Last edited by sswee; 02-17-2006, 12:13 AM.

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  • pickleboy
    replied
    Re: The great SFPM Debate

    no bro you are still thinking in terms of rpm. the wheel is still spinning at the same speed. if you had a 4" wheel and turned it at 3000 rpm,it would be 3000 sfpm. and a 8" wheel at 1500 rpm would be 3000 sfpm. like your example of the wheels on a car. now spin them both at the same speed and you get 4"=3000 sfpm 8"= 6000sfpm. clear as mud right.

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  • rides20
    replied
    Re: The great SFPM Debate

    But isnt it still spinning slower by using a larger wheel?

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  • sswee
    replied
    Re: The great SFPM Debate

    From years in the machine shop, let's see if I can clarify. The formula Caswell gives is a short cut for the calculations. The long way is to find the circumference by multiplying Pi times the diameter. Multiply the answer by the RPM running. This gives you the IPM (inches per minute). Divide this by 12" to get the SFPM (surface feet per minute).

    On autos one tire size is approx. 3 mile difference on the speedo.

    6" wheel at 3000 RPM's

    3.14 * 6 = 18.8495" circumference
    18.8495" * 3000 = 56548.6677" IPM
    56548.6677" / 12 = 4712.3889' SFPM

    6" / 4 = 1.5
    1.5 " * 3000 = 4500

    The Caswell formula is more closer to actual since when you bear into a wheel you are not running at the 6" diameter but at 4" to 5".

    SS

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  • fly
    replied
    Re: The great SFPM Debate

    Yea just check your mph and you will see, ask the cop next time he stops you....Ha Ha Ha.....

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  • rides20
    replied
    Re: The great SFPM Debate

    If you have 12" rims on a car, and you travel at X rpm...then you put on a set of 20"s (polished ofcourse!) at the same RPM, the 20s are going to GO farther in the same duration of time, but will actually make fewer rotations than the 12's...This sounds like the S.A.T's ! HAHAHAHAH..And ehhhhemmmmm....... I've been "upgraded" to Amateur. HAHAHAHAHAh

    So all in all....the formula says Slower is better??
    Last edited by rides20; 02-16-2006, 07:24 PM.

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