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How change in tyre size affects ground clearance

Discussion in 'Tyres & Alloys' started by shams, Jul 16, 2012.

  1. shams

    shams Esperto

    Messages:
    2,388
    Bangalore
    Heres how to calculate ground clearance change due to change in tyre configurations-


    Rolling radius is the distance to ground from center of tyre.

    It is depicted in the below picture with a red line:

    RR.jpg


    From the definition of Rolling radius we know that its enough to compare the difference in the rolling radii of two tyres to know how the ground clearance has been affected.
    Its calculation is demonstrated below with an example:


    For example if the tyre is 215/45 R17:


    Section Width of tyre = 215 mm
    Aspect Ratio of tyre = 45
    Rim Diameter of tyre (D) = 17 inches = 431.8 mm (1 inch = 25.4 mm)

    Sidewall Height (SH) = 215*(45/100) = 96.75 mm


    Hence rolling radius for the above tyre will be:


    (SH + D + SH)/2 = (2*SH + D)/2
    = (2* 96.75 + 431.8 )/2
    = 312.65 mm


    Some more examples:


    For Active/Dynamic:
    (165*.8*2 + 14*25.4)/2 = 309.8


    For EP (current Emotion)
    (195*.60*2 + 15*25.4)/2 = 307.5


    With 195/65 R15 tyres
    (195*.65*2 + 15*25.4)/2 = 317.25



    We do not know with which tyre profile the speedo is caliberated for Indian puntos so its difficult to guage how the speedo will be affected.

    Others please feel free to add to the above information !!
    1 person likes this.
  2. Pran

    Pran Superiore

    Messages:
    748
    Bangalore
    Grande Punto 1.3
    I have checked the error few days back using my MMI navigator for a 195 65R15 spec.

    Odo reading = 151km
    GPS reading = 164km
    Last edited: Jul 17, 2012

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