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D&D 3E
I'm looking to use an Armor as Damage Reduction system for my game. I… 
16th-Jun-2006 05:52 pm
I'm looking to use an Armor as Damage Reduction system for my game. I am aware of the variant in Unearthed Arcana, but I'm looking for a system where armor gives only DR and not also an AC bonus. Any ideas on a good scale for the DR (so what DR leather armor gives, what DR full plate gives)? Or how to have magic bonuses (such as on "full plate +2") apply?

My current thought is to have DR range from 1/- (leather armor) to either 4/- (full plate) or 8/- (full plate), or possible have the armor reduction be a range (so leather reduces by 1d2, fullplate by 2d4 or something). I was originally thinking that I could just have the "+1" magic bonus add to the armor's DR, but I'm starting to wonder if that will work. Any suggestions?
17th-Jun-2006 02:12 am (UTC)
I ran some numbers actually. What I figure is that losing 8 points of AC means the opponent hits you 40% more often, so on average does 40% more damage. So if the opponent does (on average) 20 points of damage or less, you've got the advantage (he's losing 8/20 of his damage, which is a 40% reduction). If he does 21 of more points of damage, he's losing 8/21 of his damage, which is a 38% loss--a number that only goes down as the average damage dealt goes up.

So for creatures that do less than 20 damage a hit, you're doing better. For those that do more, you're doing worse. As a point of comparison, a Green Dragon's bite attack (primary physical attack of an "average" evil dragon) does 20 points of damage average at age Very Old (CR 19). On the other hand, a Huge Earth Elemental (CR 7) does 20 points of damage on average. Based on these two data points, it seems like armor will generally improve for most the game (which I'm okay with), but there are always big baddies who can bust through it.
17th-Jun-2006 02:16 am (UTC)
Furthermore, the chance of getting hit increases by .05*Bonus [Bonus is the armor bonus], so we're looking for the Damage where Bonus/Damage = .05*Bonus. Simple math gives us that Damage = Bonus/(.05*Bonus), or Damage = 20. Thus the threshhold for your armor doing well is always 20 damage on average, no matter what armor you're wearing.

So the question is, do more creatures do >20 damage a hit or <20 damage a hit?
17th-Jun-2006 02:19 am (UTC)
You went into that way more accurately than I had the patience for, but you're dead on.
17th-Jun-2006 02:23 am (UTC)
I like math a lot ;p

You also have a good point, that any abilities that rely on simply hitting the guy rather than doing actually damage are going to be more powerful. It's something else to consider, but I think it will work out since I think most creatures do less than 20 damage average a hit.
17th-Jun-2006 02:25 am (UTC)
Yeah, but the DM is going to know which ones don't.

When it comes down to it, D&D is a subjective game balanced by the DM rather than an objective game balanced by mechanics.

*shakes fist at Rule 0*
17th-Jun-2006 03:40 am (UTC)
Fortunately, most of those things involve a save (I'm running a sorceress in August that has a snake familiar, so I've been looking it all up) and save-based special attacks are often kind of sucky. They get less powerful as the characters advance, basically. Which is kind of the opposite of the armor thing, but it's not a big enough discrepancy to cause a problem. I think. (It's late.)
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