For 235 wide tires, you should go 235/60/R16 if you want to keep overall diameter nearly the same as original, 235/70R16 is way too much (more than 6% bigger than oem, you may have rubbibg issues). The size for 16" that most people buy is 215/65R16.
http://ejelta.com/tiresize/index.html?w ... maxdelta=2
http://ejelta.com/tiresize/index.html?w ... maxdelta=2
