Be that as it may, there's plenty of description on how to use it, but none on how to derive it. I always intended it to be a quick and dirty evaluation, but for some reason that never made it into the text. So, here's my quick and dirty attempt to put that down.
A quick note: size isn't a reflection of the inherent toughness of a vehicle, that would be armor and the damage meter. Size instead reflects the difficulty in shooting something worthwhile on the vehicle. An 18 wheeler might be pretty easy to hit when you spray it down with automatic fire, but most those bullets are going to punch through the side and hit nothing but air. Even if you concentrate fire on the cab, you'll chew up upholstery and the like, but a whole lot of those bullets won't actually do anything more than cosmetic damage. Thus, size is exactly that: size. It's not toughness.
So, with that out of the way, here are my previously unwritten thoughts on size:
Size 0 is the baseline. This means there's no modifications to the attack and damage rolls in combat. Characters, even trolls, are size 0, and by extension so are most small vehicles. By small I mean mostly motorcycles. Even if a bike is significantly heavier than a character, there's not a lot of empty space on these vehicles, so a hit probably means a real hit.
Size 1 are vehicles with just a little storage capacity and empty space around their shells. I'm thinking something like the Jackrabbit here.
Size 2 is getting into car territory. 2 door, 4 door, compact, sedan, all of that. At this point there's a fair bit of air enclosed in that body, and there's probably nothing but a bench seat behind the driver. You can tag the people on a called shot, but there's nothing back there worth hitting otherwise. This category also covers 2 seater helicopters and speedboats. This is going to be the most common size players encounter unless they're in exotic settings.
Size 3 vehicles are really big. We're talking limousines and other extended body vehicles like citymasters. Anything this big tends to stand out; people don't commute using these conveyances.
Size 4 is a category reserved for cargo vehicles. These things have a ton of open space, usually with the intention of filling said space. Cargo trucks, hovercraft, and larger troop carriers all fall into this category.
Size 5 is the biggest it gets. If you look at it and need to swivel your head side to side to take it all in, it probably belongs here, assuming most of that space isn't filled with vital components.
Now, that covers big things. What about small things? I don't have much need for that, since my rigger is dead set against ever using a drone, but I did give it a little thought at one point regardless. While it's entirely untested, I think that you can reverse the size rule and apply it to smaller vehicles such as drones. Negative size modifies an attacker's roll as follows:
- Add the absolute value of the size to the threshold required to hit
- Increase the method by 1 when determining damage for every 2 points of negative size
A shooter with a Razor of 3 fires at the drone. He must score at least 3 yang on his roll, since the drone's size adds 2 to the base threshold of the attack check. If the drone also engages in defensive actions, the attacker needs to beat the drone's yin +3 (because +2 will yield a net of 0 yang, which is a miss).
The shooter hits, scoring just one yang. Normally this would mean he does base weapon damage, but the drone's negative size means he gets to treat his Razor as a 4 when looking to code up his damage score. He couldn't apply any 4s to his attack roll, but he's free to roll them into his damage now that he's scored a hit.
This means that small drones are much harder to tag, but don't take punishment as well. Now, you could just make damage meters on these things small, but this lets you have drones that can still take more than a single hit, provided it's not a big one. Plus, you could use this on a much broader scale than an ever decreasing damage track. After all, you can't shrink something past a 1 box damage track, but size could drop infinitely, theoretically.