If you follow the manufacturer's weight chart, you will see that they give a certain PSI to handle the axle weight and it is always the same PSI regardless of the number of plies or rating. An F or a G rated tire would need the exact same PSI to carry the same weight. The only difference is that the G tire can carry more weight, if you increase the air pressure. Inflate the new tires to the proper PSI according to the actual weight on your front axle and you will not be able to tell any difference in the ride.