Looking for help choosing between Armour Penetration runes and flat AD

Oddnerd·8/10/2015, 10:47:31 PM·1 votes·543 views

Hi all, I started playing again and am updating my runes/masteries. I notice that for AD characters flat AD runes tend to dominate the build guides, while the once ubiquitous armour pen runes seem to have fallen out of favour. What is the reasoning behind taking more initial AD rather than +19 arm pen, when it seems at face value that reducing armour by flat 19 would be huge in the early part of the game (people usually start with 30-40 base)?

Any explanation of the theory behind flat AD/arm pen selection would be great.

1 Comments

rampaging poet8/11/2015, 11:26:37 PM1 votes

I think the reason people usually take flat AD over flat pen is that the AD helps with last-hitting and provides stronger early-game damage. Taking someone from 40 armour to 21 armour increases your damage to the enemy by just over 10% of your base physical damage (from 71% damage dealth to 82% damage dealt). You'd need about 150 AD for that increase to match flat AD marks and quints. Armour Penetration runes will probably still give you more damage late-game because they stack multiplictitively with your AD, but you'll have a harder time last-hitting and the enemy will deal more damage than you in the early game.