How much bite damage does an Oversized Goblin Feral Gnasher Barbarian do?

Question

Should "Hard Head, Big Teeth" for Oversized Goblins be 1d6 (1d8 with Savage Bite) or is the alternate racial trait 1d4 no matter the goblin's size?

It's not obvious to me how these three things interact:

1. Oversized Goblins are a Goblins Subrace:

   Oversized goblins are Medium size, and grow to 4 to 5 feet tall. They tend to be particularly obese, weighing between 225 and 275 pounds. Instead of the normal racial ability score modifiers for goblins, oversized goblins gain a +2 bonus to Strength, a +2 bonus to Dexterity, and a –2 penalty to Charisma.

2. "Hard Head, Big Teeth" is a Goblin Alternate Racial Trait:

   Hard Head, Big Teeth: Goblins are known for their balloonlike heads and enormous maws, but some have even more exaggeratedly large heads filled with razor-sharp teeth. Goblins with this trait gain a bite attack as a primary natural attack that deals 1d4 points of damage. This racial trait replaces skilled.

3. Feral Gnasher is a Barbarian Archtype for Goblins:

   Savage Bite (Ex): At 1st level, a feral gnasher gains a savage bite attack. This is a primary natural attack that deals 1d4 points of damage. If the goblin already has the hard head, big teeth racial trait, the damage increases to 1d6. At 10th level, the damage from a feral gnasher’s bite increases to 1d6 (or 1d8 if the goblin has the hard head, big teeth racial trait) and deals ×3 damage on a critical hit. This ability replaces fast movement.

Answer 1

Nothing explicitly calls out this combination and tells us the answer directly. But I think a comparison to a more simple case leads us to the answer.

Consider a non-oversized goblin feral gnasher with hard head, big teeth. Per the description of feral gnasher, the damage with the savage bite is 1d6. Suppose this goblin was then the beneficiary of an enlarge person spell, making them Medium. That explicitly increases their savage bite damage to 1d8.

So a goblin feral gnasher with hard head, big teeth that is Medium not because of enlarge person, but because they are also an oversized goblin, should also have a savage bite that deals 1d8 damage. Being a size category larger increases weapon damage by one die step; there is no reason to think that shouldn’t apply here. It’s a little awkward because you are calculating the effect of the size increase (an inherent racial trait) after the class feature savage bite, but that’s just a convenient work-around for the fact that neither savage bite nor hard head, big teeth directly address oversized goblins.