Probably a bad idea unless you are willing to make a few suspension adjustments to make up for it.
Going from the stock sizes to the 120/65-180/55 combination will have the effect of raising the front 6 mm and lowering the back 3 mm. This is exactly the opposite of what is generally done to make the bike handle better. By lowering the front 6 mm and raising the back 3 mm you would probably be back to the stock handling characteristics except for the additional weight.
Going from the stock sizes to the 120/65-180/55 combination will have the effect of raising the front 6 mm and lowering the back 3 mm. This is exactly the opposite of what is generally done to make the bike handle better. By lowering the front 6 mm and raising the back 3 mm you would probably be back to the stock handling characteristics except for the additional weight.
