I have aftermarket 18" wheels and tires on my 2006 GLS Sonata V6. Anyone know the max width i can go on the tires? Currently have 225/45/18 with no problems?

 

It depends on the width of your wheels, and how much room there is between the sidewall and the fender/fenderwell or suspension components. Offset of the rim, (negative or positive) has a large impact on clearances also.

Climb underneath, (with the weight of the car on the suspension) and start measuring. If not sure how to do that, explain what you want to do to the local tire/custom wheel dealer dealer. Look for the shop that handles a lot of aftermarket wheel sales, and is willing to get out a measuring stick... be leary of the shop that just banks on a computer keyboard for what will fit. Those will be the guys that know what's going on.