I found some wheels i like and they are 17X7 and the next size up is 19" . I was hoping for 18" is 17" too small? will they still look right? I have only bought and used rims on trucks so I dont know much about cars. With the truck I just said "yeah 31's will fit on those" and that was the end. With the car I hear so much talk I start to wonder if I order wheels will they be the right ones. What is offset? Somebody just school me on what i need to know.

 

IMO 17's are a perfect fit still allowing you to run 40 series tires. Keep in mind if your ride is a commuter you want to try keep the ride smooth. I have not heard if there is a way to recalibrate the speedo/odometer so you want to retain close to the original tire diameter. This link will help http://www.miata.net/garage/tirecalc.html .

 

If you look at the sticky one thread above this one, you'll find your info. I've got 215/40/17's on my car. In my opinion it looks perfect. The width really fills out the wheel well and is almost flush with the body of the car. I debated getting some 18's on there, but the tire place talked me out of it. They told me it'd be about $500 more! Actually they just told me that I may notice a decline in the ride quality and that they are easier to blow out than 17's. I really like the look of 18's on these rides though. If you can manage to not get rims without a lip they ultimately look bigger than they are. People mistake my 17's for 18's quite frequently. I think it just ends up depending on what you want out of your tires and rims. If you are a big commuter, I wouldn't recommend anything bigger than 17's... if not, then go for it!!