Armor Penetration Information

Ok, many of you have already seen this, but since it is not only interesting, but factual, I wanted to provide a couple extra thoughts on the current posts.

I begin with a direct quote from Ghostcrawler:

We didn’t want Armor Penetration Rating to be too powerful against low armor targets, like it had been in BC. We also didn’t want Armor Penetration Rating to be too powerful against high armor targets.

So, we decided on a system where there is a cap on how much armor the Armor Penetration Rating can be applied to. So, the first X armor on the target is reduced by the percentage listed in the Armor Penetration Rating tooltip, and all armor past that X is unaffected. Another way of understanding that is we multiply the percentage in the tooltip times the minimum of the two values: the cap, and the amount of armor on the target after all other modifiers.

Computing the cap is a little tricky unless you are already familiar with how World of Warcraft armor works. There is an armor constant we’ll call C. C is derived as follows (in some pseudocode):

If (level<60)
C=400+85*targetlevel
Else
C=400+85*targetlevel+4.5*85*(targetlevel-59);

For a level 80 target, C=15232.5. For a level 83, C=16635.

The cap for Armor Penetration then is: (armor + C)/3.

A level 80 warrior creature has 9729 armor. C=15232.5. So, the cap is (9729+15232.5)/3=8320.5. Let’s say a player has 30% armor penetration from armor penetration rating and no other modifiers that complicate the calculation (talents, Battle Stance, Sunder Armor, etc.). The game chooses the minimum of 8320.5 and 9729, so 8320.5. That is multiplied by 30% = 2496.15, and so that much armor is ignored. The effective armor on the target is 7232.85 (9729-2496.15). From a player point of view, the armor penetration rating didn’t ignore the full 30%, but instead ignored 25.66%. (85.5% as effective as expected).

So, I see one point of interest here that we should be (possibly) happy about. Namely that there is no "cap" per-se on Armor Penetration, except that you cannot possibly ignore more than 100% of the Armor penetration cap amount. Thus we can stack our Armor Penetration up to (but not over) the 100% mark (which is already pretty tough to get to anyway.

I'd LOVE to have enough AP gear to actually test this theory, but I'm having a significant amount of difficulty getting to that point.

If you read the early post on how to calculate this sort of thing, let me amend whatever I may have said about the Armor Penetration rating. Since the modifications to AP (they buffed it significantly), the new "base" value that needs to be used appears to be about 3.754 (it is slightly more than 3.75, but that's a rough estimate of how much more).

So, Arms warriors can expect that in heavy combat situations, on top of the 10% armor penetration we have from battle stance we're going to to want 5 sunder stacks (eliminating 20% of the target's "removable" armor) and we'll assume that for stressful situations we will also allow shattering throw to remove an additional 20%, so we want to know how much AP rating it would take to get to 50% passive armor penetration (yes, you may have trinkets that boost it occasionally, but let's first find out what the number to stay below is).

And the answer turns out to be 616.

Now, I was goofing around looking at some items I could use, and I noticed that I can get up to about 400-500 easily, which nets us about 32%-40% passive AP.

With this in mind, watch out for trinkets like the Mjolnir Runestone (which are phenomenal if used correctly). You don't need to worry about them being "not as good as advertised", only worry that (if you notice), adding 612 AP rating for 10 seconds won't do you a lot of good if you're already stacked to 400-500 AP, since you'll be pretty much hitting your cap around even without any "extra" armor penetration rating, just from the trinket.

For those adventurous few that are seeking more than 50% armor penetration, here's the guide for caps up to 100%, I'll start at 50%, though.

50% = 616 AP rating

60% = 739 AP rating (I suppose so you can dps in Berserker stance?)

70% (so you're capped with only 5 sunder stacks) = 862 AP rating (with a 612 boost from the runestone, this would be fairly simple, and then you can ignore Shattering Throw for all intents)

90% (so you're capped even without sunders) = 1108 AP rating.

100% (so you're capped even in Berserker stance without sunders?) = 1231 AP

My thoughts on this are that basically, if you want to shoot for the 862 rating cap, that could be very nice. If you assume that you're doing this with the 612 rating boost from the trinket, that means you'll have about 250 Armor Penetration rating all the time, with the trinket boost coming into play every so often. You still have a reason to keep your sunders up, and you'ld be looking at having:

Passively: 30.3% armor reduction (of the armor that is reducible, see above)

W/Sunders: 50.3% armor reduction

W/Sunders & Shattering Throw: 70.3% armor reduction

W/Runestone (Grim Toll also works) proccing: 80.02% armor reduction

W/Sunders & Runestone (Grim Toll also works) proccing: 100% armor reduction

So essentially, since these have an internal 45 second cooldown on procs, and they last 10 seconds, we can say that (provided you have your sunders up) you could expect to have 45 seconds of 50.3% armor penetration followed by 10 seconds of 100% armor penetration every 55 seconds or so.

This would amount to an average of 59.33% Armor penetration all the time (obviously with the sunders).

Notice that this is equivalent (basically) to stacking the 616 AP rating. Also be very careful when making statements like "Grim Toll/Mjolnir's Runestone is BiS trinkets for blah blah blah" because each of these separately proc a 612 AP rating, and you have to look at your chance of having them proc separately or simultaneously.

For example, if you have them both equipped and have the 250 AP rating to go with them, and they proc separately, then you could enjoy a comfortable 20 seconds of 100% armor penetration out of every 55 seconds of combat, or approximately a 68.37% Armor penetrated (of that which is penetrable) overall. However, if they procced at the same time, even with all that massive overload, you would have exactly the same 59.33% Armor penetration that you'd have with only the runestone, since you can't penetrate more than the 100% of the penetrable armor.

Because the benefit from either of these trinkets is so massive, I might suggest going ahead and not worrying if one takes you over the count, but I don't know whether or not I'd gamble on both at once. For example, this set of (admittedly high level) gear would give you 584 Armor Penetration (before enchants and gems) and isn't the highest you could get. However, it would give you 57.44% passive Armor penetration with the 5 sunder stacks giving you a 77.44% passive Armor Penetration, and the 10 seconds when the trinket pops, you get the extra 22.56% for 10 seconds, which would give you an average AP of about 81.54% overall. Notice it's not a big increase from the passive amount, but it is an increase even over using Grim Toll/Runestone only even if they proc separately all the time. Also, it's nice to know that you can always add an extra 20% AP with Shattering throw during any of those internal cd's of the Runestone that you know you want the extra oomph during.

Another nice thing about your gear is that it should be balanced enough to privide a healthy amount of crit rating (here you get 682 or approximately an extra 14.86%), enough hit and expertise rating to get the rest of the way to hit cap and expertise cap with some gems and enchants, and plenty of strength and Armor (which will be more important for us after patch 3.2, which is the only reason I bring it up) to give us a healthy dose of Attack Power.

A secondary piece of information to take from this is that we now know (A) how to anticipate a mob's armor values a little, and (B) how to cheat the system in PvP. Suppose you're worried about a warrior stacking 100% armor penetration in an arena. . . get the highest armor value you can before you go after him.

Note that this is because of the way they average these values together. If the armor value for the mob etc. were less than half of the C value they give for that level, then the overall armor penetration possible would be 100% of the armor the mob has. So for level 80 this gives a lower armor value of 7616.25. Any target with this amount of armor or less would essentially be "disarmorable" with 100% armor penetration. On the other hand, if you are wearing 21000 armor, that same 100% armor penetration will only allow them to remove 57.51% of your armor value, which may come as a shock to them.

So assuming that level 80 mobs do actually have differing armor values, Armor Penetration will still be on a sliding scale of effectiveness, with the more armored foes being less vulnerable to it, but now we know how it works.

I think I've found the gear set I'm going to work towards here (at least until the new patch when better is available). This accomplishes (once enchanted, gemmed etc) about 422 Armor Penetration (34.28% penetration + 10% battle stance, + 20% sunders gives 64.28% Armor Penetration most of the time, with 100% for 10 seconds out of every 55 seconds, giving an average of 70.77% without considering Shattering Throw), balanced out with 1019 crit rating (about 22.2% extra bringing me to 34.24% unbuffed), about 1285 extra strength and enough hit and expertise to be just barely over the caps (albeit the soft cap in the expertise case).

Ok, not too bad, now to actually accomplish it. :D