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Porsche Cup tyre sizing on a Quattro, HELP

Discussion in 'A3/S3 Forum (8L Chassis)' started by Adamh_A3Q, Nov 6, 2009.

  1. Adamh_A3Q
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    Adamh_A3Q New Member

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    Hey,

    hopefully somebody can help me, i can only find websites that will calculate old an new tyres but not front and rear.

    I currently have Porsche Cup 17s on my A3 Quattro with original tyres. Front 205/50/17 (7J) and Rear 255/40/17.

    I want to lower the profiles and stretch the rear tyres and i know i need to change all 4. so any help would be very much appreciated.

    ideally i would like 235/40/17s or mayb 235/35/17s on the back but im not sure what size the profile would have to be on the front. I dont want to change the size that much but i dont know how to keep the circumferences the same due to not wanting to break the Haldex system on my quattro. somebody also suggested maybe going to 225/40/17 on the back but i think this would stretch the rear tyres to much. its also lowered on a weitec kit (shocks and springs)

    any help would be great

    cheers

    Adam
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  2. RichA3Turbo
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    RichA3Turbo ...Watching you! Staff Member Moderator

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    Problem is with such a stretch, the tyres will be different circumference regardless as stretching pulls down the contact area towards the rim. You'd have to do some real good calculations. What size are the rears? 9.5"?
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  3. Adamh_A3Q
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    Adamh_A3Q New Member

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    i think they are just 9J. yea i did think about that aswel. anybody got any numbers that might be able to help with sizing or should i just not even bother trying?
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  4. jojo
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    jojo S3 Drift King! Staff Member Moderator

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    If you go for 235/40R17 on the rears, then the fronts would need to be 205/45R17 or there abouts. For 235/35R17's, you would need 205/40R17 for best match for rolling radius. These figures have not taken into account the stretch factor.
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