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.
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.