1" = 25.6 mm, so 5 mm is slightly less than 1/4". Measure the current position of your tire sidewalls and then use that to figure out how much further you want them to move. That is the difference you need to figure into the new wheels.
Just remember that moving the wheels further out or in will change how the suspension cycles. Further out will put a higher load on the springs due to the increased leverage, and can cause increased tire wear from the camber change.
'11 LTZ, born Aug 2010, Fairfax, KS
V6/A6, Red Jewel Tintcoat / Cocoa-Cashmere, Sunroof
Mods: WeatherTech mats, CHMSL Pulser
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