How early can you do dragon analysis: Part two
By Fistful of Force
Continuing from the previous segment, we can see that in terms of doing the dragon, the dragoneers must have at least 180 hp + ~110 hp every second they take to do it, and they must do at least 3200 (220*highest champion level).
However, this is only technically, and not realistic. In the best case scenario you will buy a pink ward and do it quickly enough that the enemy does not bother to contest.
Always try to make sure that you will have some kind of advantage when you do dragon. If you see a person top, than you can be sure that he won't be able to get there in time (it takes about 30 seconds to get to drag from top at 350 movespeed). If their jungler, sup, adc, or ap is dead, and your teammate is alive you can do drag.
However, seeing as this is not always possible, you will also have to deal with contesting.
Any damage you take from them is added on to the damage you take from drag. CC will add on precious seconds to the time it takes to do it.
But the greatest problem you will have when doing dragon is distraction.
Every millisecond you take a to chase a enemy teammember is a millisecond you take more damage.
Attacking at max range means that they can easily run away and kite you. But you have to chase them, and meanwhile you're taking damage from the dragon. If they are attacking from 550 range (ez's attack range), or getting poked from afar (1100, his q range) you will have to use 1.5 seconds to get to him if he's attacking and 3.1 seconds if he's poking. Not to mention the fact that he has arcane shift.
This means if you take the time to be distracted by him, you will take an extra 350 damage at the least. Quite a bit if you only have ~1000 damage. In cases like that, you must either let it go and try again later, or defeat them with overwhelming damage.