I have 18s and they should fit but dont know 100% and I cant even measure since I dont have my car. Reguardless Id rather get a new set of wheels in exchange for better braking. At 1/2 off and almost the same price of regular Cobras its a steal.
Heres the info you need for clearance.
http://www.americanmuscle.com/brembo...0-cobra-r.html