Vehicle armor class: how is it calculated?

[The Red Mage]

Exactly what it says on the tin.

According to the rules, "a vehicle has a base Armor Class based on its size and other defenses the vehicle has."

What are these other defenses? Why, for example, does a Steam Giant only have an AC of 6? Wouldn't a giant cauldron of iron count as having an armor bonus of some kind?

So, anyone know how Paizo calculates a vehicle's AC? This has been bugging me because I've been working on vehicle stats for a futuristic OGL modification of Pathfinder and I like the vehicle rules from Ultimate Combat.

[The Red Mage]

Any ideas pathfinders?

[Purplefixer]

This is an excellent question. It goes well with the questions about why touch AC is backwards for vehicles.

[Darksol the Painbringer]

From the PRD:

Attacks against Vehicles wrote:

To calculate the vehicle's actual AC, add the current driver's driving skill modifier (or Wisdom modifier, if it is using that ability to drive the vehicle) to the vehicle's base AC. Touch attacks against a vehicle ignore its driver's driving skill or ability modifier; thus a vehicle's base AC is its touch AC. A vehicle is never considered flat-footed.

AC wrote:

The AC assumes the vehicle is in motion and the driver has not modified the AC with his driving skill. If the vehicle is not in motion, it has an effective Dexterity of 0 (–5 penalty to AC), and an additional –2 penalty to its AC.

As far as the standard AC, look to the table it lists on here and correlate the size of the vehicle you're using, as well as its relative CMB bonuses in regards to its size.

So to sum up, you take the vehicle's base AC (shown in the table) plus the Driver's Driving skill or Wisdom modifier. If you're taking in Touch Attacks, only include the base AC. (Clerics are the best drivers in the game, who knew?) So if I'm a Cleric with a 4 Wisdom modifier, using a Large vehicle puts me at 13 AC (or 9 Touch). Since vehicles are essentially Construct creatures, they cannot be caught Flat-footed. Obviously, somebody who is a trained driver will have a significantly higher AC than somebody who isn't, but against touch attacks, you're just simply screwed.

**EDIT**

As Chemlak specified and after I crunched the resulting numbers, his formula matches the numbers listed in the table. So the total calculation is 10 + size + Wisdom/Skill modifier.

[Chemlak]

In the vast majority of cases vehicle AC is 10+ size modifier. I'm still trying to figure out heavy chariot.

Edited to correct vehicle with discrepancy.

[Hark]

I feel like Heavy Chariot is just a typo. It does seem that Touch AC and Flatfooted AC maybe backward. A moving Vehicle should be harder to touch, not easier, so Driver skill modifiers should apply. While a Driver caught unaware, flat-footed, should not apply their skill modifier.

Materials that a vehicle is made of affect its HP and Hardness. I actually see no reason that you couldn't actually add armor to a vehicle to improve its AC, though that is obviously not the chosen method for the game.

[Darksol the Painbringer]

Hark wrote:

I feel like Heavy Chariot is just a typo. It does seem that Touch AC and Flatfooted AC maybe backward. A moving Vehicle should be harder to touch, not easier, so Driver skill modifiers should apply. While a Driver caught unaware, flat-footed, should not apply their skill modifier.

Materials that a vehicle is made of affect its HP and Hardness. I actually see no reason that you couldn't actually add armor to a vehicle to improve its AC, though that is obviously not the chosen method for the game.

There aren't rules for it, but I don't see why there aren't, considering there are such things as Barding, why not Fortification subjects for vehicles?