first if idrop my car 2.5 inches will i need a camber kit. also i was wandering if i went with a smaller tire size how would i recalibrate my speedometer?

where are you wandering to?

You will want a camber kit unless you want your tires to wear un-evenly.

For the tire size, there really is no way to recalibrate. You can try this webpage and it will show you how much it will be off. http://www.miata.net/garage/tirecalc.html