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Ratio of motor RPM to wheel RPM?

Discussion in 'Roadster: Technical' started by Slackjaw, Jun 23, 2011.

  1. Slackjaw

    Slackjaw Member

    Joined:
    Apr 12, 2011
    Messages:
    354
    Location:
    Central NJ
    Does anyone happen to know the ratio between motor RPM and wheel RPM on a Roadster? I appreciate that it will be different for front and back wheels.

    I suppose a ratio between speed and wheel rpm would be as useful. Just trying to pin down a funny noise I can hear sometimes while driving.

    Thanks in advance
    Ian
     
  2. Slackjaw

    Slackjaw Member

    Joined:
    Apr 12, 2011
    Messages:
    354
    Location:
    Central NJ
    Thanks for the pointer. Had to google the terms on that page as I am not a car person, or at least I wasn't...

    So I understand this to mean that at 312 rpm, the wheels are turning 100 times per minute... And at 14000 rpm (= 120 mph) that equates to about 75 Hz.

    I heard a funny noise while driving last night and couldn't work out if it was coming from the tires or the motor, so this will help me. At 30 mph it will be about 19 Hz if coming from the wheels and about 60 Hz if coming from the motor.

    Thanks again!
     
  3. S-2000 Roadster

    Joined:
    Apr 10, 2009
    Messages:
    636
    Don't forget that the tires have their own particular tread pattern, which could generate yet another frequency based on the number of sipe gaps in the rubber. Changing to a different brand of tires can drastically change the frequency and intensity of certain pitched noises in a vehicle.
     

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