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Speed calibration (speedometer)

Discussion in 'Model S: Driving Dynamics' started by rpavlicek, Feb 19, 2013.

  1. rpavlicek

    rpavlicek ***** Neophyte

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    I assume the speedometer is calibrated based on wheel rotation. Is it based on the front axle? (makes sense since they won't slip)

    Does anyone know how to re-calibrate the car if you get different size tires on the speed-measured-axle (I guess Tesla would be the place to go)? Has anyone attempted to do this yet?

    Down the road I may consider different wheels (currently have the standard 19's), and was wondering what effect it will have on the speedometer.
     
  2. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    The wheels themselves don't have any bearing on the speedometer. It's the RPM of the tires that is important. You could have a 10" wheel (assuming it would fit over the brakes) :) and if the tire had the same RPMs as the OE tire the speedometer wouldn't change.
     
  3. Doug_G

    Doug_G Lead Moderator

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    The effective outside diameter of the tires is the same regardless of whether the wheel is 19" or 21". This is achieved by having lower profile tires.
     
  4. rpavlicek

    rpavlicek ***** Neophyte

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    Yes I get that.

    If you put 265/40 (20" wheel) on the rear, it will change the diameter (and therefore RPM). There isn't an aspect ratio for a 265 that will closely match the 245. (A 245/40R20, 245/45R19 and 245/35R21 are very close in RPM, but a 265/XXR20 will be bigger or smaller by a fair margin depending on what you choose for XX)
     

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