Start by getting your tire/rim combo road force balanced. Now that you know it's a tire or rim you need to find out if it is a bent wheel or a bad tire. Both with start out immediately if they are road forced balanced.
Your wheels are properly hub centric, right? If they are not you will never be able to get the vibrations out and your car will eat struts and shocks.
225/45R18 will make your car accelerate more slowly, make your odometer and speedometer wrong, and may rub. The error and acceleration difference will be about 4%. All other things being equal, taller sidewalls means a better ride. Beyond that, lots of tires get different internal designs from 40-series and below, making the ride even harsher.
Your wheels are properly hub centric, right? If they are not you will never be able to get the vibrations out and your car will eat struts and shocks.
225/45R18 will make your car accelerate more slowly, make your odometer and speedometer wrong, and may rub. The error and acceleration difference will be about 4%. All other things being equal, taller sidewalls means a better ride. Beyond that, lots of tires get different internal designs from 40-series and below, making the ride even harsher.
