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Thread: How to scan speeds faster than 158 mi/h (255km/h)?

  1. #11
    Joe (Moderator) joecar's Avatar
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    Apr 2003


    Quote Originally Posted by Blue70SS View Post
    What is the "336"? Is this the gear ratio or a multiplier used on the "gear_ratio"? (so if my rear end gear ratio is 3.25, would I use 325?)
    Or, if I'm interpreting correctly from previous posts, the "gear_ratio" is the currently selected gear's ratio, and the 336 is the differential gear ratio. Does a separate PID need to be created for "gear_ratio"?

    Hi Blue70SS,

    The 336 is simply the constant of conversion from mph to rpm and inches (and/or vice-versa); it is not related to rear axle ratio.

    so for example (using say 6th gear):

    TR6060 6th = 0.63
    your rear axle = 3.25

    using engine RPM:
    gear_ratio = 3.25 * 0.63 = 2.0475
    road_speed[mph] = (engine_speed[rpm] * tire_diameter[inch]) / (2.0475 * 336)

    using have transmission output rpm:
    road_speed[mph] = (trans_output_speed[rpm] * tire_diameter[inch]) / (3.25 * 336)

    I don't know if there's a pid for the M6 trans output speed in RPM.
    Last edited by joecar; February 22nd, 2018 at 12:06 PM.

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