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

[spinozajack]

Hi guys, I was curious about making a balanced DR system for my home game, so google brought me here. Hi!

After reading the comments I agree that a % based approach is the only solution that can be balanced with the base game, especially when some players are using it and others aren't. Even if you run this system for the whole table, it should still be as balanced as possible to the base game so that the monsters do not become under or over powered. And you can still run published adventures without conversion.

What I think is the best solution is to use instead of 1 point of AC above 10, as some specific value in DR, that you scale the damage proportionally as others have mentioned. Of course this is slow and unworkable to do it for every attack, so the best way to avoid that is just to pre-calculate a lookup table for incoming damage to outgoing damage for each armor type.

That would be very fast in play and perfectly balanced versus traditional AC, except for status effects on hits that others have mentioned. The additional flat DR from Heavy Armor Master could be simply added to the table so even the subtraction step could be removed.

You can even make it more realistic with such a table, like for example heavy armor gives -2 to base AC, but you boost the DR value curve up a bit to make the net expected damage taken on incoming attacks to work out to the same thing as they do not. That makes status effects like wolf grapple checks happen even more often against plate wearers, but that's actually cool and realistic too. That's a penalty though, but a good one. People wearing heavier armor should move more slowly and be easier to hit. But take much less damage when they are hit.

I hope if there's an Unearthed Arcana article on the subject of DR it uses a % based table lookup, which is accurate, balanced, and a drop-in replacement for the existing AC system which requires no work except looking at a table for the player (or DM) who wants to use it on a given creature. Rounding damage should be rounded to the nearest integer, not rounded down. If you get hit but take 0 damage, you treat it as a hit for things like grapple checks but not things like poison saves.

 

[spinozajack]

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.

I believe you have to look at the statistical effect on incoming damage vs a range of to-hit values vs your base AC, to figure out the DR value for a given attack's base damage.

So, make it proportional to the expected damage reduction of AC 10 to your armor's AC, on a range of attacks. Then you simply print out a lookup table with the precise value that AC 11 - 25 values would reduce average damage by (averaged across a great many attacks), and use that table of Incoming Damage vs Taken Damage, with each row in the table be in 1 HP of incoming damage increments.

You just need one printout for each armor type, or armor type + shield. So 9 tables total, hand the one out to the player who's using DR and have them do a lookup in the table to see what damage they take given what armor they are currently wearing.

Perfectly balanced to the base game maths when you consider a large number of attacks. And fast too. Table lookups are easy and straightfoward. If the player gets tired of it, they just revert to the base AC system again. Easy opt-in optional rule, works per-player too to keep them balanced versus the group. Except a slight penalty to status effects on hits which would of course happen much more often. Heavy Armor Master's flat 3 DR could still be useful and incorporated into the table itself, to give a greater chance at completely negating a hit, including status effects. You could treat 0 damage as a miss from a rules standpoint when deciding whether a save is necessary for status effects. Or do it on a case by case basis. Maybe wolves don't get easy bite grapples on plate armor wearers unless their teeth sink into an exposed area and draw blood. Poison saves shouldn't happen when 0 damage is taken either.

 

[I'm A Banana]

Hi guys, I was curious about making a balanced DR system for my home game, so google brought me here. Hi!

Welcome to ENWorld! Enjoy the nerdiness.

As for your proposal: a table would work OK, but I've got a bit of an aversion to having to look up values on a table in play to see what happens (random generation tables excepted, of course!). I'm leaning toward the greater resistance/resistance/lesser resistance model currently, as it seems to keep viability over mulitple levels without making one immune to goblins.

 

[Jester David]

I believe you have to look at the statistical effect on incoming damage vs a range of to-hit values vs your base AC, to figure out the DR value for a given attack's base damage.

So, make it proportional to the expected damage reduction of AC 10 to your armor's AC, on a range of attacks. Then you simply print out a lookup table with the precise value that AC 11 - 25 values would reduce average damage by (averaged across a great many attacks), and use that table of Incoming Damage vs Taken Damage, with each row in the table be in 1 HP of incoming damage increments.

You just need one printout for each armor type, or armor type + shield. So 9 tables total, hand the one out to the player who's using DR and have them do a lookup in the table to see what damage they take given what armor they are currently wearing.

Perfectly balanced to the base game maths when you consider a large number of attacks. And fast too. Table lookups are easy and straightfoward. If the player gets tired of it, they just revert to the base AC system again. Easy opt-in optional rule, works per-player too to keep them balanced versus the group. Except a slight penalty to status effects on hits which would of course happen much more often. Heavy Armor Master's flat 3 DR could still be useful and incorporated into the table itself, to give a greater chance at completely negating a hit, including status effects. You could treat 0 damage as a miss from a rules standpoint when deciding whether a save is necessary for status effects. Or do it on a case by case basis. Maybe wolves don't get easy bite grapples on plate armor wearers unless their teeth sink into an exposed area and draw blood. Poison saves shouldn't happen when 0 damage is taken either.

This seems needlessly complicated, almost as a way to discourage the player. It's a little adversarial for my comfort; it'd be easier to just say "no".

 

[spinozajack]

Welcome to ENWorld! Enjoy the nerdiness.

As for your proposal: a table would work OK, but I've got a bit of an aversion to having to look up values on a table in play to see what happens (random generation tables excepted, of course!). I'm leaning toward the greater resistance/resistance/lesser resistance model currently, as it seems to keep viability over mulitple levels without making one immune to goblins.

Thanks!

I agree that rules should be kept simple in the basic game, but no matter what you do, you are going to add complexity by enabling DR; it goes with the territory.

My question is, is looking a value in your armor's DR chart quicker than calculating 25% or 75% of every single attack's damage? I believe it is. Much so. Also your system wouldn't scale smoothly with incoming damage compared to relative AC improvement. Cutting a number in half is reasonably fast for most people to do every incoming attack. But 25%? 75%? I don't think so. It's a division and rounding operation for the 50% case already, but the other one would have people busting out calculators so fast it would make your head spin. Until they stop using the system because fractions are unwiedly. Anyone can do lookups easily and quickly.

However, having said that, I realized some other things that must be kept into consideration.

1) Crits would have to bypass the table entirely, to match the base AC system. Good. Crits should do that, like an arrow piercing through the slits in a visor. Completely ignore armor.

2) A Barbarian's thirst-for-blood CON bonus to AC could also be a lookup in the table. So his new to hit value would be 10 + Dex, and his sturdy consitution would add incoming damage reduction (if the player wants). Since each point of AC improvement beyond the previous would already be balanced, you could even arbitrarily split up AC values into DR or non-DR buckets with a simple table that the community could vet for maths errors.

3) What's more D&D, than a lookup table? Lookup tables are very fast operations. You need only print out the column for your own armor type as well, so no need to scan in two dimensions for the value you want, you just read down. You could even make it into a wheel going from 1 to 20. I can see lots of fun potential in this.

4) The base AC could be kept at 10 + dex for light armor, 10 + dex (max 2) for medium, and 10 for heavy, or it could be 8 + dex, or 8 + proficiency bonus when you have heavy armor on and the Heavy Armor Master feat. You could re-estimate the relative % reduction values in the lookup table to account for any of these changes relative to the base system's expected incoming damage (averaged over many attacks).

 

[I'm A Banana]

My question is, is looking a value in your armor's DR chart quicker than calculating 25% or 75% of every single attack's damage? I believe it is. Much so

Maybe!

For me, I just think handing my player a table to consult is going to be a non-starter (an extra thing she "needs"), but telling her "take 3/4 damage" is something she can do pretty quickly (she's an engineer, after all!).

 

[spinozajack]

Engineers also love charts and graphs and tables though

Calculating 25% / 50% / 75% is, aside from the slowness and extra effort, going to get tedious, no matter how much of a mental wiz she is. I personally don't want D&D to remind me of work too much, especially the tedious repetitive parts. I like to calculate damage that I deal, not damage % reductions. 50% reduction like resistance works because it's simple. That's why it's in the game already, I think.

Anyway, difference of opinion and all that. Happy gaming! I would be willing to make the chart and post it here for the maths nerds to rip it up a bit

If I were to actually use this rule as a player, I could definitely want to print out the incoming vs final damage out in a circle with values on two rings, and loop it around. Then maybe a picture of the armor and/or shield I'm using with some blood on it. I think that would be really fun to use when receiving damage personally. "Oh let me see, you say I take 15 damage? Oh no, I take... 10".

 

[TheSleepyKing]

Most methods of exchanging AC for DR just don’t really work. They essentially make the D20 roll irrelevant, since hits will happen most of the time. The only thing that matters then is the damage roll.

The way I would do it is this: get rid of AC altogether and create a new stat. Let’s call it defence.

Defence = 10 + proficiency bonus + dex bonus (with armor limits)
A shield gives +1 (buckler) or +2 (medium/tower) defence.

Attack rolls are made against defence.

Then armor serves as DR equal to half it’s normal AC bonus (I haven’t really worked this out, but I’d probably break the normal rule and round this up). The DR applies to all types of damage.

This method is pretty simple and has the benefit of being somewhat realistic. It’s not without wonkiness, of course, and it’s probably going to horrify people who want any changes to be perfectly balanced in terms of DPS with the way the game was before. I’d say it would have these major effects:
- Players and creatures all become a little tougher, so combat goes on longer. Heavily armored characters get tankier, but even squishies are likely harder to hit.
- Given that players will likely be more heavily armored than most of their opponents, it does make combat a little easier for them.
- It will probably be the case that “str fighters” (high DR) will be better early on, while “dex fighters” (high defence) shine later in the game. This can be balanced by the DM by occasionally using large numbers of low-level enemies rather than big guys with alpha strikes.
- Low frequency/high damage attacks are generally going to be more valuable than high frequency/low damage attacks. Monks will be pissed. (Of course that's really true of any DR system).

 

[fewilcox]

In 5e, how much DR should a point of AC be worth?

Before I can answer that, you need a bit of history, both mine and the roleplaying industry's.

Our very first roleplaying purchase was GURPS Basic Set 3e, but the first game we ever actually played was HackMaster 4e, which was in '04 or early '05 so we had started a collection of GURPS 4e books.

In GURPS armor (from a bear's hide to a tank's ablative plates to a starship's force field) gives DR (Damage Resistance) X, subtracting X from the damage of incoming attacks. But as it thankfully lacks an AC equivalent, it's hard to make a comparison.

(For the curious: GURPS is built around skills. A ranger tries to roll 3d6 under his Bow skill (generally 14-16 for a starting adventurer) to kill his supper. If his roll succeeds and the prey wasn't caught completely unaware, it gets to make a Dodge roll (8 for an average human) to try and avoid the hit. A deer's hide is DR 1, so the GM will subtract 1 point from the ranger's damage before applying it to the deer.)

HackMaster 5e, on the other hand, does exactly what your player is asking. GURPS is our go-to system so it's the one I know best and the one I think in and compare everything else to, but my current campaign is HM5e so I think I can be of help.

If you've played AD&D 2e and any sort of point-buy system (like GURPS), then HackMaster 4e will be familiar. It is basically D&D 2.5 merged with a point-buy game. Since it is at heart an evolution of AD&D it uses the standard d20 vs AC, but of course had good ole THAC0 (which I was delighted to find the D&D 5e PHB's index).

For 5e Dave Kenzer and friends decided to try and keep the same feel as HM4e and the old school D&D that spawned it, but with completely modern mechanics, including armor that lowers defense but provides DR. It once again lacks a direct AC equivalent, though. Instead of boring, old static target numbers, most non-damage rolls are opposed, with both players rolling 1d100 for skills or 1d20 for everything else plus mods. In combat the defender wins any ties, and can even critically defend, earning a free, immediate counterattack. (It also works in the last two editions of D&D since post-THAC0 AC is basically a Take 10 defense roll.)

Since it is still d20-based its armor table may be of use to you even though it lacks fixed target numbers. You can get the rules, pre-gens, adventures, and everything else you might need for free on the Kenzer & Co website, except the chargen rules. The rules come in the free PDF HackMaster Basic and include the armor table, but here are the bits vital to this discussion (plus a few more armors that were previewed before the PHB released):

(NOTE: Since HM5e uses second-by-second combat instead of rounds, lower Initiative is better.)

Armor	DR	Defense	Init	Category
None	0	0	-1	None
Thick Robes	1	-1	0	None
Leather	2	-2	0	Light
Padded	2	-3	+1	Light
Studded Leather	3	-3	+1	Medium
Ringmail	4	-4	+1	Medium
Banded	6	-4	+2	Medium
Chain Armor	5	-5	+2	Heavy
Scale	5	-6	+3	Heavy
Splint	6	-5	+2	Heavy
Plate	7	-5	+2	Heavy

Hopefully you can make something out of that.

It just occurred to me that I never specifically said that I am in full support of armor providing DR. It's how it is handled in my two favorite systems so it's what I'm used to and has become my preference.

 

[77IM]

I love the hit-point-pool idea. If each point of AC from armor is worth about a 10% decrease in expected damage, that's roughly the same as having 10% more hit points. If the "typical" PC has 6 HP per level, some creative rounding gets us:

Padded, Leather: bonus HP = 1/2 your level (minimum +1)
Studded Leather, Hide: 1x your level
Chain shirt: 1.5x your level
Scale, breastplate, ringmail: 2x your level
Half plate: 2.5x your level
Chain: 3x your level
Split: 3.5x your level
Plate: 4x your level

Defense DC:
Light armor = 10 + Dex
Medium armor = 10 + Dex (max +2)
Heavy armor = 10
Shield = +2

I like that this is quick to calculate and the calculation is done up-front on the character sheet instead of every single round, like DR or soak dice. It also makes spell attacks much nastier -- they hit more often and many have non-damaging effects that are really bad. (General consensus is that attack-roll spells tend to be weaker since saving-throw spells often do half damage even on a successful save.)

These bonus hit points would represent an increase in your maximum hit points. There would be no special rules around them, you just have more hit points when wearing armor. If you remove the armor (or it gets destroyed) your relative number of hit points remain the same. Like if you are at half your hit points and remove your armor, you go down to half your new hit point total; if you then put on some better armor, your current hit points go up to half your new higher hit point total. In practice, PCs RARELY switch around armor like this: most players decide what kind of armor they like and stick with it.