I know this horse has been beaten to death so I'm sorry, but I am just confused right now.....all the threads I found in a search were for 18x9.5 wheels. I need info on 18x9.

I bought my Z used and the previous owner got MB Weapons 18x8 +30 offset all the way around. There are 225/35/18 in the front and 245/35/18 in the rear.

I figure the cheapest way to get the staggered look is to get the same wheel in 18x9 for the rear. The options for offset are +15 or +38. I assume I want the +15 for a slightly deeper look than the fronts, but my real confusion is on the tire size.

Tire Rack and Discount Tire both recommend 245/45/18 for 18x9 rims. Since I have 245 on there now, won't that defeat the purpose of going with a wider wheel? Can't I go with like a 265/40/18? Can I even go with a 35 series tire? Should I run the 245/35/18's in the front instead of the 225?

Here are the wheels

 

Proper tire width?. Tire manufactures recommend a range of wheel widths for their tires. You can find this information at the manufactures home page or the Tire Rack.

Tire size? Use one the many tire calculators on the internet. Compare the overall tire height of your present tires to those that you are considering buying. The key is to match the original tire height.

 

Thanks, I have checked on the Toyo site as well as Tire Rack and Discount Tire, but none of them recommend a 35 series tire, so does this mean I should not be running a 35 series tire at all?

 

OK, OK, I think I've seen the light......

I went to this tire calculator......
http://www.miata.net/garage/tirecalc.html

and I basically want to come as close as possible to the factory sizing?

Factory:
F - 225/45/18
R - 245/45/18

Aftermarket:
F - 245/40/18
R - 275/40/18

These aftermarket sizes should match perfectly?