BMW Repair: rim offset, 18 rims, wheels and tires

Question
hi, i have a 90 750 il and was looking to go to 18" rims with 245/40/18 tires is there anything i have to worry about? also did my car come stock with synthetic oil? can i use it if it did not? and lastly if i put synthetic in can i go back to conventional?  thanks for your time! steve

Answer
Steve, you can use synthetic if you like, but the car came standard with 15w-40 conventional motor oil. I don't see any problem switching back and forth. I would stick to one or the other though. Synthetic is better. I don't know what wheels and tires fit on your vehicle.
-Evan