18x8... 235/40 or 235/45?
 

need help deciding between 235/40 or 45s for my 18x8 +40 wheels. i like the idea of a little more sidewall on the 235/45. and i dont want a wider tire since this car is underpowered. 235/45/18 sound good? car wont be slammed, just slightly lowered.

ps: looking at falken ziex 912

between the two, definitely 235/40/18.

235/45/18 is 7% (too much) larger in diameter than the stock tire, and therefore will noticeably affect the speedometer reading and gearing of the car. rule of thumb is you want to stay as close to stock tire diameter.

personally i would get a 225/40/18 on that 18x8, it will fit perfectly squared on the wheel, still have good sidewall to protect the wheel and add even slightly less unnecessary rubber-to-ground contact.

I'm with Steve - 225/40 on an 18x8 is perfect for functionality and looks, and little to no weight gains if you get the right wheel/tire combo.

225/40/18

Sorry jacking thread. If I go 18x9 on the rear, what will be ideal tire size? 255/35?

Yes. 245/35/18 works as well, but is very slightly stretched.

225/40/18 is the better size.

i just got Forgestar F14 18x8.5/9.5 wheels, and the tire shop only had some 235/45/18 Pireli PZero Nero laying around so i just put them on while waiting for 235/40/18 front and 245/35/18 back.
But i must say..i like these 235/45's ..with the light wheels ,the ride is smooth and the car seems to be much faster with less unnecessary tire spin and road grinding. Seems a bit bulky,and it kinda took away my staggered, but i think its ok,,doesnt really rub, only if i drastically turn the wheel maybe but i cant notice while driving. i dont see any rub,,,but i will lift the car to see if it touches anything at full turn. I did take to other used tire shop and they do alot of tires and they said its fine and to keep the 45 because here alot of cracked rims because of low tires.

im in north jersey..mad potholes and crap so i dont want to lower another car or get 19's. Car looks mad aggressive without lowering so i might sick with this and maybe get atleast 245/45/18 for the rear. People keep saying nice car, so in person its looks real nice. ::: but ill try and attach a photo