D&D 5E Trading AC for DR in 5e

[Blue]

Also keep in mind that this means that she will be subject to many more "on-hit" effects than other PCs with the same armor. In a fight with wolves, for example, she's likely to be subjected to many more Strength saving throws (to avoid being knocked prone) than a similarly armored ally.

I'm still thinking about the whole system especially trying to work out fair change for one PC but not the whole party. But for this particular issue I'd suggest that if damage is reduced below 0, it's treated as a miss. So no Wolves knocking prone or OAs that stop movement.

Though I think that would work better with a soak die then a flat DR, so some small attack could occasionally still have effects and some large attacks could occasionally miss. But that's adding another layer of rolling which could slow things down.

 

[the Jester]

Note that the Heavy Armor Mastery feat does this as its primary benefit. Personally, I'd tell her to take the feat if she wants DR, but I'm pretty harsh on "treat me different from the other pcs" requests.

 

[TwoSix]

This would really need to be playtested. Especially in 5e, where having +3 AC is great at all levels but soaking 1d8 damage isn't amazing. +3 AC is a reducing of damage taken by 15%, while 4 damage each attack is only 15% if you were taking 27 damage (such as 4d8+9 or 3d12+8). If you're taking more damage than 27 then the AC would have been better, while if you're taking less, the soaking is better.

Just to nitpick, but that isn't quite true. +3 AC is equal to a 15% reduction in the frequency of attack success, but that does not correspond to a 15% increase in taken damage, because the hit frequency for all attacks is already below 100% (and usually well below). Just as an example, if the enemy has a +5 to hit bonus against your AC of 17, its hit frequency is 45% (Needs a 12+ on the d20 to succeed.) Add a +3 bonus to AC, and it now has a hit frequency of 30% (A 15+ on a d20). That makes the damage reduction for the bonus +3 equivalent to 33% (Previous damage was 0.45*Damage Value, New damage is 0.30*Damage Value. So the change is [0.45-0.30]/0.45).

Believe me, you do enough theorycrafting for your World of Warcraft tank, calculations like Armor, Damage Reduction, and Time to Live values (the actual most important value for defensive calculations) become second nature.

 

[kerbarian]

Here's another thought. Simple and seems like it might work out okay:

Every point of AC above 12 turns into 1 DR. Instead of DR, plate grants resistance. The DR and resistance only apply to damage that's the result of an attack roll (i.e. only when AC would have helped you). Shields still add to AC, not DR.

So light armor is unaffected, a breastplate is AC 12 (+dex max 2) plus DR 2, chain mail is AC 12 plus DR 4, and plate is AC 12 plus resistance.

It's a bit of a compromise all around -- it doesn't turn all armor into DR, just some of it. As with any DR, it will be more effective at low levels than high levels. However, it keeps all the armor types distinctive and interesting, and if the character in question eventually plans to get plate I think resistance ends up being a decent way to model it at high levels.

 

[Flexor the Mighty!]

Interesting thread. I've been thinking of taking the AC and HP system out and remaking it where HP are meat and AC is DR. Trying to make it more realistic where some types of weapon are more effective against certain armor and some types are totally ineffective against certain armor. Shields would become obsolete when you got to plate armor level and two handed and piercing weapons were necessary. Wouldn't be a very cinematic style of game to be sure.

 

[Jester David]

Just to nitpick, but that isn't quite true. +3 AC is equal to a 15% reduction in the frequency of attack success, but that does not correspond to a 15% increase in taken damage, because the hit frequency for all attacks is already below 100% (and usually well below). Just as an example, if the enemy has a +5 to hit bonus against your AC of 17, its hit frequency is 45% (Needs a 12+ on the d20 to succeed.) Add a +3 bonus to AC, and it now has a hit frequency of 30% (A 15+ on a d20). That makes the damage reduction for the bonus +3 equivalent to 33% (Previous damage was 0.45*Damage Value, New damage is 0.30*Damage Value. So the change is [0.45-0.30]/0.45).

Believe me, you do enough theorycrafting for your World of Warcraft tank, calculations like Armor, Damage Reduction, and Time to Live values (the actual most important value for defensive calculations) become second nature.

My math isn't good enough to really get the *exact* numbers down, but I am mostly aware of what you describe.

Each modification of a d20 roll is a 5% variation, so a +3 AC bonus is 15%. But, as is demonstrated in your math, the +3 AC has no impact on the attacks that are already misses. All the AC bonuses in the world have no mathematical impact if the attacker rolls a 2. So it really only varies the hit percentage, the percentage of rolls that would hit. Since you can ignore half the rolls that are not impacted, it moves from 15% to 30% (give or take).

But, since the +1 = 5% math is fairly common knowledge, and the above is complicated and requires a lengthy post to explain, I find it easier to ignore and go with the more commonly accepted (yet less accurate) math. Otherwise people will go "whaaaaa...?" and auto-ignore the argument based on a hastily perceived math error.
At least when (as in this case) the difference between 15% and 33% is irrelevant to the argument. The 15% reduction to hit rates was already better than damage soaking, so pointing out it would actually be 30-odd% and *even better* while risking incomprehension was unneeded.

 

[TwoSix]

At least when (as in this case) the difference between 15% and 33% is irrelevant to the argument. The 15% reduction to hit rates was already better than damage soaking, so pointing out it would actually be 30-odd% and *even better* while risking incomprehension was unneeded.

The real takeaway is that AC increases aren't linear in value. AC bonuses are actually more valuable the higher your current AC is. (Until the attacker can only hit on a 20, then the value of an AC bonus drops off a cliff.)

 

[I'm A Banana]

What would the impact be if instead of a numerical DR, I had heavy armor grant "greater resistance" (-75%) vs. piercing/bludgeoning/slashing, have medium armor grant resistance, and light armor grand "half resistance" (-25%), with the rule that 0 damage = a miss? Maybe scale better with level? Math would be pretty easy, maybe even easier than normal DR in a lot of circumstances....

 

[Greenstone.Walker]

So light armor is unaffected, a breastplate is AC 12 (+dex max 2) plus DR 2, chain mail is AC 12 plus DR 4, and plate is AC 12 plus resistance.

I worry that this has a massive impact on the bounded accuracy concept, because a medium armour wear is now completely immune to anything that does 1d4 damage.

 

[Quartz]

Note that the Heavy Armor Mastery feat does this as its primary benefit. Personally, I'd tell her to take the feat if she wants DR, but I'm pretty harsh on "treat me different from the other pcs" requests.

I agree.

Heavy Armour Mastery is restricted to heavy armour and boosts Str.

How about this as a feat:

General Armour Mastery
Prerequisite: Any Armour Mastery feat .

You can use your armour to deflect strikes that would kill others. You gain the following benefits:

While you are wearing armour with which you are proficient bludgeoning, piercing, and slashing damage that you take from non-magical weapons is reduced by your proficiency bonus. This replaces the damage reduction granted by HAM.

While you are wearing armour with which you have Mastery, as well as the above you have Resistance to bludgeoning, piercing, and slashing damage.

This could be implemented at first level by allowing a human character to take two feats instead of the stat bumps.