First thing to note, my sedan is on a stock 350Z suspension so it's lowered approximately 1" inch from the stock G35 sport suspension. Okay, now onto the question of will this fit.

Stock Wheel: 17x7 +45 offset
Stock Tire: 215/55/17

Aftermarket Wheel: 17x8.5 +40 or +30 offset
Aftermarket Tire: 255/45/17

According to the tire calculator the speedometer difference will be less than 1%.

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

According to the offset calculator the +40:

The clearance from stut housing to the inside of the wheel will be 14mm LESS
The outside edge of the wheel will EXTEND an extra 24mm

and the +30 offset:

The clearance from stut housing to the inside of the wheel will be 4mm LESS
The outside edge of the wheel will EXTEND an extra 34mm

http://toy4two.home.mindspring.com/offset.html


I know two members on this board are succesfully using 8.5 wide rims.

https://g35driver.com/forums/showthr...t=stock+offset


Will the wheel/tire combo I'm thinkinb about fit properly? And if so which is the correct offset? I'm thinking the 40mm as it seems the 30mm will stick out the fender. TIA.

 

The 40mm offset will work the 30mm definately will not. Enkei took and measured a sedan for clearances. I remember the rear specs and measurement's, but since the front used a stagger with 225 wide tires I didn't bother to remember the front specs that they used or the clearances.
But in the rear they used a 18"x9" rim with a 38mm offset and a 245/45-18 tire mounted. That combo was 2mm away from the rear fender lip. A 255 wide tire is of course 10mm wider then a 245, since we are only concerned about tire to fender lip clearance, we half that increase to see how it effects clearance.

With 8.5" wide and a 30mm offset.
The clearance from stut housing to the inside of the wheel will be 14mm MORE
The outside edge of the wheel will EXTEND an extra 2mm. This mean's that the the 2mm of clearance to the rear fender lip is used up, but you still have to add on half of the 255 tires extra width, putting the combo 5mm over the fender lip.

With 8.5" and a 40mm offset same as above but with 5mm of clearance from the rear fender lip

In the front I see no reason for the 40mm setup not to work. With a 255 tire on, you are only 7mm further inwards then those running 8.5" wide rims with 245's. Looking at the ultimate in running close clearance on the inside of the fender well/suspension, 9" wide 30mm offset on 275 tires, your 14mm further away from the inside then that setup.

I noticed that the MX's are only $125 a tire, lucky you

 

Darren, the +30 will definitely stick out. You should be OK with the +40. I don't know if you got a good look at my car at Red Robin but I'm on 18x8.5 +38 and it's perfect. Another 2mm inset will be fine.

 

Eloy, Gsedan35... thank you as always. Now hopefully I get that bonus check in Feb as promised. Then I can finally get a good tire/wheel setup!

 

Just an FYI... On my sedan, mild lowering w/ HKS Hypermax LS coilovers of about 1", I'm running Volk CE28N 18x8.5 w/ a +40mm offset at all four corners. I have not had any rubbing issues with 245/40R18 tires.