The original steel rims that comes with mehran are only 4 inch wide and 12 inch in diameter with tire profile 145/70/r12.
if you are going for after market rims then search for Japanese rims which have width of 4.0 jj or 4.5 jj or max 5 jj while the tire size you can change is 155/70/12 or 155/80/12. this size combination will not put any major difference in fuel consumption, suspension or body load.
if you go for higher than 5 inch, they will create problems with suspension.