Question About Tire Sizes

[PULMEOVR]

Hi guys,

My stock tires have 58,000km on them and they are just about toast. I'm looking to replace them with 18" Saleen rims. What do I need to recalibrate my speedometer? And is it worth doing so, since my speedometer will read approx. .4% too fast with the new rims/tires?

Thanks!