Would using 18 inch rims all around look bad or hurt the cars stability and handling? The rims in the back would be 18x9 and the fronts would be 18x8.

 

I think it could look fine.

Stability and handling? just make sure you get a rear tire that is close to oem circumference

 

The back spoler holds presur under high speeds down at the angle of the car the hood acks as a front spoler honding presur on front of car, this is what i was told by a man that races high speed races ,

 

OK, I cant spell verry good but , you understand what i just said ???

 

The ABS needs original spec wheel circumferences front and rear to be able to detect when any of the wheels are slipping. If you don't maintain the original wheel circumferences, then the ABS will always be trying to correct what it sees as a stablility problem.

 

both wheels spin @ same speed so ABS wouldn't be affected. Now going from an open diff (3 channel) to a LSD or locking diff (4channel) can screw with ABS Module and TCS Module.