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RS4 whells and gearing

imported_GezzerS4 Oct 6, 2004

  1. I am looking to put RS4 18 wheels on my S4, question is what will it do to the speedo accuracy and is it correctable ???

  2. GregC

    GregC Member

    The diameter of the wheel with a tyre fitted if is the important bit. Tyres are sized as follows: eg 255/45 ZR 17. 255 is the width in mm, 45 is the percentage of the width that the tyre is deep, ZR as the speed rating and 17 is the inside measurement (the outside diameter of the alloy basically).

    As an example if you replace a 225/45 ZR 17 with an 18" alloy of the same width you would need to use a 225/35 ZR 18 to retain similar gearing - there would be a small change but given that a speedo is normally only within 5 to 10% you shouldn't have too much of a problem.
  3. AndyMac

    AndyMac Moderator Moderator

    I have 18" RS4 reps and with 225/40/18's fitted the difference in overall rolling circumference is 2000mm over 1985mm (+15mm), or 637mm diameter over 632mm stock. This is less than 1%, the max recommended difference is +/- 2.5%.
    If I do 100mph on the speedo, my road angel says I am doing 98mph, so it is actually more accurate than with the stock 16" wheels. The bigger concern is the additional weight of the wheel, which can be considerable, but worth bearing in mind especially with replica's.

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