i believe u have 225-45-17 right? c70 has steering bump stops that prevent u from turning too far and rubbing the wheel well... i think u may wanna try the tire size calculator here http://www.miata.net/garage/tirecalc.html

i think 235-40-17 may work...try the site. i think on the c70...ur 5 spoke rims should be 7.5 inches instead of 7 (altho a 7" will fit 225) to fit a 225 properly...should be...



the pilot sport u have should be better than most tires in the dry and in the wet... but definitely not worth going to snow. the cold temp will cause the rubber to harden...and some of the compounds that are in a tire will become separated from others as the tire warms back up... rendering less traction. if u need something for light snow...the pilot sport a/s is a great all-season tire to provide some traction in the light snow... they are one of the best...but also one of the most expensive.