If i put 18 inch wheels on my car will anything change? Like will the speedo read differently and my odometer be off?

 

I am doing the same thing.Going with18x9 235 40 19 tire. Your speed should only be off by about 2 miles,if as much.

 

But say you were traveling at like 70 mph, then how much would it be off? Wouldnt the difference in speed be linear to how fast you're traveling? The faster you go the more of a difference the bigger wheels make?