http://www.kouki.co.uk/utilities/vis...ize-calculator

So using this site..im a bit interested in what others think of the results

I entered my stock size (255/35/19 S-Line) & then OEM Prestige (245/40/18)

The calculator says that the OEM presitge wheels are running 1.2% less

At 30mph(s-line) the prestige wheels would clock 29.6mph
At 60mph(s-line) the prestige wheels would clock 59.3mph

???
So a stock prestige is running slower the a stock S-line, or is the S-line actually going faster the it should be??

Now if I change from Prestige to S-line I get 1.2% greater
At 30(prestige) the s-line wheels would clock 30.4
At 60(prestige) the s-line wheels would clock 60.7

Now i've been trying all different setups from Audi from the prem, prem+, prestige and s-line...none of these side by side run the same speedometer reading?

Please everyone give me your thoughts on this