how wide can i go on my tires when they are 225/50 R18?

 

they're 7.5" wide wheels, so 225 is optimal. If you want to go wider, you'll need wider rims

 

Yep^^

 

245/45/18

 

The OEM 18s are 18x8, a 225/50, 225/45, & 235/45 is the ideal mount on that wheel, a 245/45 will work if you're wanting the widest tread block. With the widest recommended tire on the particular wheel you will sacrifice a bit of sidewall stability if really pushed to the limit, that's why the 225 & 235 choices are best here.

Always best to look at the tire manufacturers data page for the tire you want to buy. They list the recommended wheel width range for each tire, it can vary between tire lines and sidewall series too.

Here's an example, click on the link, scroll down to 18" sizes and you can see on the far right the recommended wheel widths. You can see the 8" is the minimum width and the darkened number is the ideal mount for that specific tire.
https://www.toyotires.com/tire/patte...e-summer-tires

 

They're either 18x7.5 front 8.5 rear for staggered or 7.5 all around for square.

 

The sedan runs those sets, here's the coupe sets
2008 through 2013 Infiniti G37 Coupe Rim and Tire Specifications, weight, offset and information

Here's the Sedan sets~
http://www.infinitig37.com/Sedan-wheel-tech.html

 

in that case, 245's

 

This is a big pet peeve of mine...Doling out wrong information/advice like it's correct. If you're not sure then qualify your post with that. I guess this should be in the random rants thread...

 

it's called being mistaken. It happens sometimes. You can be sure of things and still be wrong.

 

Check Victory's post history, his input around here is extremely helpful, I've learned quite a bit from him over time. Easy to get some things turned around as there's a lot of parts around here that swap from model to model and some are specific.

 

I apologize, my post was not intended to be reproachful towards you personally.
I have lost money in the past from someone giving me wrong information with certainty so I've learned to always double-check/verify any help/information I receive but I know a lot of people don't do that. Thank you for your effort in helping the OP