You probably don't want to reduce the circumference of the tires... The only best way is to probably upsize to 19s.
For example, if you change 235/45 to 235/40 or 235/35, the distance covered per revolution is less than what your car is programmed to (suppose it's 225/50 R17)
You can probably live with 225/45 18, since that will drop the sidewall from 4.16in on your 235/45 18 to 3.99in on the 225/45 18. There may be a little stretch putting 18x8 onto 225, but it should be fine. But it shouldn't look as beefy after a drop.
Here is a comparison.
http://www.1010tires.com/Tools/Tire...50R17/235-45R18/235-40R18/225-40R18/225-45R18
See if that could help you.
For example, if you change 235/45 to 235/40 or 235/35, the distance covered per revolution is less than what your car is programmed to (suppose it's 225/50 R17)
You can probably live with 225/45 18, since that will drop the sidewall from 4.16in on your 235/45 18 to 3.99in on the 225/45 18. There may be a little stretch putting 18x8 onto 225, but it should be fine. But it shouldn't look as beefy after a drop.
Here is a comparison.
http://www.1010tires.com/Tools/Tire...50R17/235-45R18/235-40R18/225-40R18/225-45R18
See if that could help you.
