I know this is going to surprise you but I think the encumbrance rules in B/X are about the best for any version of D&D.
Really B/X gives two methods for calculating the encumbrance for a character:
Method 1 - Add up all of the "coins" for all of the equipment carried. Similar to other versions of D&D. The nice thing about B/X is that they give the slush number of 80 coins for all of the miscellaneous equipment and provisions.
However, I always use method 2 as seen on the right side of the "OR" in the first column of the table - Strictly determined by what armour is worn and if they are carrying treasure. No numbers, no math - ridiculously simple. Your dwarf enters the dungeon wearing platemail - his movement rate is 60-ft. Hopefully, when he leaves the dungeon his movement rate is 30-ft because he is now wearing platemail and carrying treasure.