Combustion Timing

This is going to be a bit of a wonky post. Worst of all, it’s the worst sort of wonky post: the kind that I’m not absolutely sure is accurate. I will try my best and explain my reasoning but if anyone sees anything wrong with it please let me know in the comments.

The question is a simple one: when should I look to cast my first combustion at the beginning of a boss fight?

Until recently I didn’t think much about it because I didn’t think there was anything I could do that would make much of a difference. I wanted to cast it as soon as possible for a couple reasons.  First, the earlier I cast it the more likely combustion will be available to cast at a later time when there are some buffs up or just toward the end of the fight where I might be able to cast a third combustion. Second, I generally cast Lifeblood at the beginning of the fight which gives me an extra 480 haste, and I want combustion to take advantage of that.

When I got 2 pieces of the Time Lord’s Regalia, however, that calculation changed.  The tier bonus applies a stacking buff that increases haste by 50, up to a total of 500 with ten stacks. Ideally you want your most powerful spell to be cast with this buff as high as possible.

This is not quite true, however. The interaction between haste and combustion is that with sufficient haste, combustion will yield an extra “tick” of damage.  Haste beyond that point is useless for the purposes of combustion until you get to the next level where an extra tick is granted. This is what some people would call a soft cap. Thus, the question for me is at what point during the stacking debuff will Saxsy get that extra combustion tick?

This is actually a very complicated question.

Elitist Jerks’ Fire Mage Compendium is a good place to start. It says that you get an extra combustion tick for each 10% of haste you have, starting at 5%. Notably, it provides the wrinkle that makes things complicated: haste rating on gear is multiplicative with raid buffs and talent buffs, so you can’t simply add all source of haste up to get a real reading. Typically you would have a 5% raid buff from a hybrid caster (boomkin, shadow priest, elemental shaman) and a 3% haste buff from talents. Elitist Jerks assumes you have these buffs and has calculated the appropriate haste ratings necessary to get extra ticks of combustion:

• With 812 haste rating, you get 2 extra ticks. (15% haste total)
• With 1996 haste rating, you get 3 extra ticks. (25% haste total)
• With 3180 haste rating, you get 4 extra ticks. (35% haste total)

Haste beyond that is likely unobtainable without time warp or a similar effect, at which point you will likely want to cast combustion whenever you can, so I’m not going to consider it.

Let’s take Saxsy’s gear now. She has an 1847 haste rating. To get a third extra tick from combustion, she would need either 3 stacks of Stolen Time or Lifeblood. If I cast Lifeblood directly on the pull, it is highly likely that I will have 3 stacks of Stolen Time before Lifeblood wears out, which means for the purposes of Combustion I should cast it as soon as the conditions are ideal for it (3 dots and a big ignite).

Side note: In theory to get a fourth tick I could reforge my gear to get above 2200 haste (3180 necessary for the 4th tick - 500 from 10 stacks of Stolen Time - 480 from Lifeblood). This would be a relatively simple matter because I have reforged 537 haste into crit on my gear. I’m not sure it would be worth it but it is something I will consider.

That will appear to be that, then. There is one slight problem, however: we do not always have the 5% spell haste buff in our raids. Our standard setup is with a shadow priest who provides that buff, but if he is not there, the people we have as backups do not provide that buff. Elitist Jerks assumes the presence of the buff in its combustion calculation, which means I have to recalculate for the lack of the 5% buff.  These numbers assume the presence of the 3% buff from talents, because if you don’t have that you really shouldn’t be raiding. Here’s my calculations:

• To gain an extra tick from combustion, you need 249 haste from gear.
• To gain 2 extra ticks, you need 1493 haste from gear.
• To gain 3 extra ticks, you need 2737 haste from gear.
• To gain 4 extra ticks, you need 3981 haste from gear.

These numbers may not be exactly right because of rounding; I have always rounded up to be conservative, but the calculation for whether you can round down is something I haven’t yet fully grasped (it’s not simply whether the gear rating is has a fraction below .5).  So now let’s apply this to Saxsy’s gear.

Saxsy will always get 2 extra ticks.  To get a third extra tick, she needs 2737 haste, or 890 more than her current gear. This can only be done with a combination of Lifeblood and Stolen Time. Lifeblood will give 480, leaving 410 for Stolen Time; thus, she needs 9 stacks of Stolen Time for the extra tick.  This suggests that I should wait until I get 9 stacks, cast Lifeblood, and hope for a good combustion.

Note that waiting like this might get me an extra 15k-20k damage, depending on how lucky I am with getting a good ignite on the target. There’s a serious question as to whether waiting that long for Stolen Time to stack would provide a net dps benefit; the percentage chance of losing a third combustion on a boss would not need to be very high to offset the extra damage from waiting. So I’m still not sure it’s a good idea. But at least I now know the ideal conditions.

Subsequent combustions will almost always have a full 10 stack of Stolen Time and Lifeblood, so there’s something to be considered about getting to that 2200 haste level from gear. I may play around with that.