I would only use spacers if they are the ones that slide in between the wheel and the hub on longer studs. Other ones like the ones that bolt on and then you bolt the wheel to them... no. ESPECIALLY not the non-hubcentric ones that AM/Ebay sells....
The correct way to do it is to get a better wheel/tire combo like has already been stated. But... if you must use spacers, you get a good hubcentric spacer and a set of longer ARP studs for the hubs they are going on. Press old studs out, new studs in and there you go. You need at least 6 threads of engagement and that is the BARE minimum.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.