War of the Burning Sky
My homebrew system is to split traditional armor class AC between difficulty-to-hit (DTH) and difficulty-to-damage (or damage reduction DR). Here’s how they work.
DTH: Difficulty to Hit
A character’s base DTH is 10. This is the DTH of an average person trying not to be hit. In comparison, the DTH a stationary object is 5. Each adventurer then adds their dexterity modifier to their DTH, then adds their wisdom modifier up to the dex modifier. For example, if an unarmored cleric has a wisdom mod 4 and dex mod 2, their total DTH is
10+Dex+(Wis ≤ Dex) = 10 + 2 + 2 = 14.
DR: Damage Reduction
Armor adds damage resistance to attacks that do land, at the cost of possibly lowering your DTH. Basically, once your character has been hit by a successful check against your DTH, the attacker rolls damage. Depending on the armor you’re wearing and the damage type, your armor reduces the damage done by the DR amount listed. For example, say your DTH is 11 and you are wearing half plate armor. Someone shoots a bow at you and rolls a 18 to hit (which succeeds, as 18>11). The bowman rolls 8 damage, but since your DR is 12 against piercing, your armor absorbs all the damage, so you take none. If the damage were 15, your armor would absorb the first 12 and you would take 3 damage.
Lastly, if your armor is constantly absorbing hits, it should have some way to track that damage. Instead of implementing some sort of HP for armor, we consider a saving roll whenever the armor is critically hit (by an attacker rolling a natural 20). Each armor has a “durability”. When the armor is critically hit, the armor wearer rolls a d20. If the roll is higher than the durability of the armor, the armor goes down one condition. The conditions are
Good armor is in quality condition, although it is likely scuffed and stained. Damaged armor can still be worn and used as normal, but has significant wear, possibly including tears or holes. Damaged armor can be repaired by a blacksmith (or tailor) to become Good again for a reasonable fee. Ruined armor has ceased to be effective at all, and provides no DR to the wearer; however, it still limits the max dex of the wearer. Ruined armor is almost worthless, and would cost nearly as much as a new set to repair.
In standard modern D&D rules, adding armor to a character increases their “armor class” (AC). The armor class is used to determine how difficult it is to hit a character, so more armor means taking less hits. Before considering armor, a character’s AC is 10 plus their dexterity modifier. Different armor types have different restrictions on dexterity modifiers; in the most extreme case, wearing full plate mail a character can’t use their dexterity modifier for their armor at all.
Why AC is too simple
There are two rolls involved in attacking. The first roll is the attack roll, and decides whether the weapon does damage to the opponent. The second is the damage roll, which determines the amount of injury done.
The game rules, however, have armor increasing your defense against the “to hit” attack roll. Logically, wearing armor doesn’t actually make a person harder to hit; in fact, if it restricts your ability to dodge, armor could make you easier to hit. What armor does do is reduce the amount of damage you take once you are hit, maybe deflecting it entirely.
This isn’t a terrible choice on the part of the game designers; realistically, you can use armor class to smear out some statistics and call the roll “to hit” a roll for the chance to actually apply damage (whether that’s hitting a dodger or finding a chink in armor). Here we propose a modular adjustment to increase realism.
New AC: DTH
The rationale for adding wisdom into DTH is that simply being dexterous is useful in dodging hits. On the other hand, knowing how to apply dexterity (Wis) is equally important; however, experience can’t be more helpful to dodging than your physical ability to be mobile and coordinated (Dex). In terms of balance, a very dexterous fool should still be hard to hit, but a wise klutz should not. Lastly, I feel if wisdom isn’t added, even an incredibly dexterous (18) monk will only have a DTH of 14, which means an average NPC hits over 25% of the time. Adding a dodge-oriented feat and/or a wisdom modifier can adjust that DTH to be more realistic.
Some items that might modify DTH include magical armor, which adds its enhancement bonus to DTH as well as DR. Additionally bracers or rings of speed or dexterity add to DTH.