If you keep the same overall diameter, your speedo will read out the right speed. Say your 15" wheel and tire diameter is 26" (just using this as an example)...if you get an 18" wheel with a lower profile tire, but the overall diameter stays the same (26") your speed will read out the same. Width doesn't affect this.

You're correct the bolt pattern is 5x114.3 and stock offset is +45.

 

rims



Id pull a wheel and make sure it says +45 on it several sites showed my 2006 camry xle as +45 They are +50 for the 16 inch alum wheels
That being said a 45 offset is fine for anything from 215 60 16 to 215 55 17 or 235 45 18 even 245 40 18 with fit with a fender roll on stock suspension height

Iam running veloster turbo rims 18x7.5 49 offset with 235 40 18 and i have .23 inches of strut clearence i got 40 sidewall because i was afraid it was going to rub i could have gotten 235/45 18 and now wish i did the spedo would have been closer to right and the ride would have been slighty better

I have a mint set of 06 xle 215 60H 16 unroyal tiger paw touring with 10/32 tread for 400 tires are brand new no curb rash on the rims at all