Rear tires bigger than front ?
 

I have some 17'' mesh style rims that were already on my car when I got it, I do most of my own work on my cars, but when it comes to rims and tires I'm pretty much clueless.

Anyhow the tires in the rear are stretched low profile tires, they look pretty weird to me, is this the offset ? or just tire width ? I'd like to understand how to get new tires that will actually fit the rims.

Offset is the position of the mounting face relative to the center line of the rim.

http://www.1010tires.com/WheelOffsetCalculator.asp

You just need wider tires. Go to a tire shop, and ask them what size they would suggest. Max width will depend on wheel width.

http://www.miata.net/garage/tirecalc.html

Thanks, that little diagram on the offset calculator helped me understand offset pretty quickly.