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Thread: Tyre Sizes for Better Ride

  1. #21
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    Quote Originally Posted by pinger View Post
    You'll have to calculate the rolling radius or diameter (or crib from Tyre Bible) and compare any difference to what is permitted.
    There is only so much latitude as the smart reads wheel speed for all sorts of functions (speedo is but one) and the various comuters on the car need to be kept happy. There is latitude to allow for tyre wear but it is limited. Get it wrong and you will have spent a lot and gained nothing.
    How do I find out how much variance is allowed?
    Last edited by Neo_the_One; 24-02-2016 at 05:01 PM.

  2. #22
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    The 453 fortwo is very much improved over the 451!! 453 wheels won't fit though, 4 stud! lol

  3. #23
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    Quote Originally Posted by lil.smartie View Post
    The 453 fortwo is very much improved over the 451!! 453 wheels won't fit though, 4 stud! lol
    But what about the tyre sizes? Not the rims.

  4. #24
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    Quote Originally Posted by Neo_the_One View Post
    How do I find out how much variance is allowed?
    I don't have a link as I always just do the calc.
    (Width x profile x two ) + 15'' converted to mm gives the rolling diameter.

  5. #25
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    Quote Originally Posted by pinger View Post
    I don't have a link as I always just do the calc.
    (Width x profile x two ) + 15'' converted to mm gives the rolling diameter.
    So from the current tyres to the ones on the newest Fortwo

    FRONT
    Difference in circumference: 85.95mm (5.03%)

    REAR
    Difference in circumference: 88.97mm (5.14%)

    Is this acceptable?
    Last edited by Neo_the_One; 24-02-2016 at 05:14 PM.

  6. #26
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    Quote Originally Posted by Neo_the_One View Post
    So from the current tyres to the ones on the newest Fortwo

    FRONT
    Difference in circumference: 85.95mm (5.03%)

    REAR
    Difference in circumference: 88.97mm (5.14%)

    Is this acceptable?
    I don't know the exact figure but I've seen 5% quoted as being the max. Hopefully someone can come up with a concrete figure.
    Meantimes, calculate the worst case wear scenario difference ie, a worn tyre and a brand new tyre. New tyres come with 8mm tread and are worn out at 1.6mm. Difference in diameters is 4 x 6.4mm ie 25. Ball park figure then is 25.6. Times Pi = 80.34 mm. That as a percentage must be close to your figures.

  7. #27
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    It is percentage difference between front and rear plus clearance in wheel arches that are important. Percentage front to rear difference is 1.25% so OK.
    Drives a Smart Cdi - 65 to 85 MPG

  8. #28
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    Quote Originally Posted by tolsen View Post
    It is percentage difference between front and rear.
    This

    Actually its a percentage difference between ANY wheel (left right front or rear) that's the party pooper.

    But as most people tendto stick similar tyres on left and right, its the front /rear difference that shows up, more so on a smart cos it's one of relatively few cars that have different wheels front to back
    You're so money supermarket and you don't even know it!

  9. #29
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    Speedo? Gearchanging?

  10. #30
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    Well yes, there will be a point where the speedo could get fairly inaccurate, and the feel of the gears a bit tall (and vice versa) lol....

    Bigger tyres - less axle rpm for a given road speed, so lower speedo reading (and the feeling of taller gears, loss of grunt ) obviously
    And vice versa

    And the ecu might get upset eventually because its expecting a certain (all) axle rpm for a given gear
    You're so money supermarket and you don't even know it!

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