Well yeah but I heard some are okay. Some just say to get close to stock rear diameter and the difference between 245/45/18 stock rear and 255/40/18 is just 2.43%. I dont plan on drifting at all so idk if 255/40/18 would be okay to run square since its pretty close to rear stock diameter

 

Do a 275/40 in rear and it will be fine

 

This. ^^

It's a slippery slope. Some VDC cars - for one reason or another - don't seem to care. But then, one day, you'll be driving along and the TCS/VDC/SLIP lights come on and bzzzzzt, the right pedal goes away.

The car's ECM is looking for a delta in wheel speed (rear slower rotation) in the range of 3% plus/minus 0.25% FRONT TO REAR and not a deviance from stock diameters necessarily. Running square "tells"' the ECM that the rear tires are spinning the same speed as the front tires OR better stated, that they are spinning faster than they should be and the ECM interprets this as a "tail out condition" and applies VDC even if traveling in a straight line.

Moral of the story: On VDC-equipped cars, best to just play it safe and run staggered (the 275/40 rear that Trav mentions) unless you are disabling VDC altogether (defeat mode, yaw sensor disabled, etc) There's very little need to run square unless you are tuning the chassis for track use. On street-driven cars, there's zero practical gain other than the oft mentioned "I wanna rotate tires." Nope, not a practical desire with the possibility of VDC intruding in your life; ya just gotta bite the bullet and count on replacing tires more often.