So, i got a new set of wheels from someone. the wheels are a 18X9.5 +30, and the tires are 245/45/18 in rear and 225/40/18. My ABS, VDC, and SLIP lights are all on. I heard you have to stay between 3% but i dont exactly know what that means, so could you guys help me out?????

 

Are you sure you have the tire sizes listed correctly? A more common combination is 225/40 and 245/40 which will work fine. The wheel/tire calculator which is listed at the top of the wheels/Tires sub-forum is a great tool to check the 3% rule. Using it your new set up is 5.98% different which is almost twice the recommend 3% difference. You could replace the fronts with 224/45 or the rears with 245/40 to get everything else back in harmony. What the % refers to is the difference in rolling diameter between the tires, here's more info:

https://g35driver.com/forums/tire_rim_calculator.php

 

Is this just with the all wheel drive G35 or also RWD? I want to go wider in the rear but keeping the same wheel height is something I'd try to do anyway since the speedometer is currently dead on.

 

It's for both. The VDC system works the same for sedan, sedan AWD and coupe and has the same requirements for all 3. Remember it's not the wheel height we're talking about, it's the tire diameter/height. You could theoretically go with 18" wheels F and 19" wheels R like some manufacturers like to do, you'd just have to adjust the tires to keep them all w/in the magic 3% number.