First off, sorry if this has been spoken about before, but new to the forum and not quite sure how to view everything.
Basically I have just bought a set of 4 18 x 9j et +15 wheels and only recently found out about the VDC issues of running square setups (I believe that is correct?)
I was wondering if anyone had any experience running the following tyre combinations and if they are compliant with the VDC system.
245 40 18 front and 265 40 18 rear.
245 40 18 front and 275 40 18 rear.
255 40 18 front and 275 40 18 rear.

OEM 225 45 18 and 245 45 18 seems to have a % difference between front and rears of 2.69179%245 and 265 = 2.41984% difference

245 and 275 = 3.6% difference

255 and 275 = 2.39091% difference

I am leaning more towards the 265 rear route as from what I have read 275's are a bit wide for a 9j wheel.
Appreciate I was a bit silly buying a set of 9j wheels rather than opting for a bigger rear but just trying to rectify the issue.
In short, what brings me back closest to OEM specification for VDC compliance and overall ride height?
Thanks in advance for the help!

 

Z33 sweet spot is a 245/275 combination (or 255F).

On a 9" rear wheel, you are at exactly the 120% practical width with a 275. (9" x 25.4mm = 228.6; 228.6 x 1.2 = 274.32mm) You can MOUNT an even wider tire but the performance fall off occurs at 120%

VDC (and TCS) equipped Zs are expecting a 3% +/-0.25% diameter delta between F&R. Generally, you won't run into problems going slightly outside that range. But yes, 245/275/40-18 (or 245/35 & 275/35-19) is a long tested best combination.

 

245/40-18 and 245/45-18 is also an option if you want to run square.