Drag force equation

Discussion in 'General Questions' started by abudabit, Sep 15, 2008.

  1. abudabit

    abudabit New Member

    Does anyone know the equation to aproximate drag force? I have an aproximation of my CdA (drag coeffcient * front area) for a tadpole I'm building. I want to find the drag at 40 mph.

    The estimated CdA is 6.9-8.3 (assuming Cd is .9) depending on the rider.

  2. softride

    softride Member

  3. abudabit

    abudabit New Member

    Thanks. It didn't have the equation, but following a link from your link I found this calculator:


    And from the javascript I think I extracted the equation:

    .5885 * (m/s)^2 * Cd * (Frontal Area in SqMeters) = Watts

    mph / 2.2369 = m/s

    sq ft * .0929 = sq meters

    HP = 745 Watts
  4. abudabit

    abudabit New Member

    Came up with 120 watts, seems really low for 40 mph. :( I think there is something wrong with this equation or one of my conversions.

    .5885 * (40/2.24)^2* (6.9 * .0929) = 120

    Arggh, hate conversions.
    Last edited: Sep 15, 2008
  5. abudabit

    abudabit New Member

    Found the problem!

    I didn't convert from Newtons. Here is the full equation:

    .5885 * (m/s)^2 * Cd * (Frontal Area in SqMeters) = Newtons

    Newtons * (m/s) = Watts

    So I am looking at around 2142 Watts, or 2.9 hp countering the effects of drag.