Re: Tire size for A4

[quinn@hns.com]

Greg Spark wrote:
> I am about to acquire a set of 17x8 rims for my 1.8T A4.
> [snip]
> I am unsure what 17inch tire gives the same rolling radius - my dealer
tells
> me 235/45x17 but I thought from other sources that people are using
> 235/40x17.

Todd Young responded:
>My calculations show the following:
>
>205/55x16 = 220/55x17 = 240/50x17 = 270/45x17 = 300/40x17
>
>This would give similar overall tire diameter so as not to
>change the speedo.
Todd, I'm afraid you may need some new batteries in your
calculator!

Courtesy of my Excel spreadsheet, here is a list of roughly
equiv tire/wheel combos for the std 205/55/16 A4 whls (see also
http://www.tirerack.com/tires/tiretech/size.htm).  This table
also shows the % difference from standard and indicates that
the 235/17" sizes are the furthest 'out' of the selection
shown (though individual tires & makers probably differ by at
least this amount so, Greg, you shouldn't worry):

     Tire Diameters = 205/55/16
     ==========================
     Tire    Aspect  Wheel     Overall   Percent
     Width   Ratio   Dia(in.)  Dia(in.)  Difference
     -----   ------  --------  --------  ----------
      195      65      15      24.98      0.41%
      185      60      16      24.74     -0.55%
      205      55      16      24.88      0%
      225      50      16      24.86     -0.08%
      245      45      16      24.68     -0.79%
      225      45      17      24.97      0.38%
      235      40      17      24.40     -1.91% **
      235      45      17      25.33      1.80% **
      245      40      17      24.72     -0.65%
      225      40      18      25.09      0.84%

Note: all of these sizes are available from Tire Rack etc.

-Mark Quinn