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  1. #1
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    What dimension of tyres do I need?

    I've just bought some 19" alloys... rim width is 8.5J. My car is an A3 8P... would I be ok with 245/35/19 (i'm unsure what these numbers mean except for the last set)? Thanks in advance!

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  3. #2
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    Re: What dimension of tyres do I need?

    245 = tyre width
    35 = tyre wall height
    19 = tyre diameter

    stange mix of metric and imperial too...

  4. #3
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    Re: What dimension of tyres do I need?

    Would 245 be ok? I'm worried that they might not fit under the wheel arch...

    A friend told me I would be better with a 235 but he talks BS sometimes so i'm here for a 2nd opinion lol. Thanks madvw

  5. #4
    S3Steve's Avatar
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    Re: What dimension of tyres do I need?

    245 = width in mm

    35 = side wall aspect ratio(side wall height is 35% of the width, in this case
    35% of 245).

    19 = wheel diameter in inches.

    To work out what tyre size you require work out the rolling diameter of your original wheels and tyres then stick as close to that as possible.

    Rolling dia of above tyres =

    2*(35% of 245) + 19 * 25.4mm

    =171.5 + 482.6

    =482.6mm

  6. #5
    S3Steve's Avatar
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    Re: What dimension of tyres do I need?

    [ QUOTE ]
    Would 245 be ok? I'm worried that they might not fit under the wheel arch...

    A friend told me I would be better with a 235 but he talks BS sometimes so i'm here for a 2nd opinion lol. Thanks madvw

    [/ QUOTE ]

    Most S3's run 235 width tyres when using 19" wheels, not sure about the new shape A3's though.

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    Re: What dimension of tyres do I need?

    Just had a quick look and i'm using 225/45/17 atmo...

    Doesn't 171.5 + 482.6

    = 654.1

    and not 482.6?

    Thanks for your help S3steve, just abit unsure as to where you got your calculations from.

  8. #7
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    Re: What dimension of tyres do I need?

    Use a wheel calculator to compare current and proposed :

    HERE

  9. #8
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    Re: What dimension of tyres do I need?

    [ QUOTE ]
    Just had a quick look and i'm using 225/45/17 atmo...

    Doesn't 171.5 + 482.6

    = 654.1

    and not 482.6?

    Thanks for your help S3steve, just abit unsure as to where you got your calculations from.

    [/ QUOTE ]

    [img]/ubbthreads/images/graemlins/blush.gif[/img] Oops my bad.

  10. #9
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    Re: What dimension of tyres do I need?

    This is the standard way of calculating rolling diameter.

    Rolling dia for 225/45/17 = 634.3mm

    So I think you would be better off using 235/35/19, as this has a much closer rolling dia to your original tyre.

    Rolling dia for 235/35/19 = 647.1mm.

 

 

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