Unlike most components, the chassis doesn't have its own component.txt file (which is where you usually set things like this). However, I still find it funny that you posted this for the following two reasons.
1. All of the stock armors come with their own text files but they don't appear to be used. I suspect that the chassis armor was implemented differently before the final release and it got changed/removed after they created a menu for it. If you tell the game to include it in the components menus then you can't apply them and adding more attributes doesn't effect bots that are using the corresponding armor. Even if you edit the .bot file to include the chassis armor as a component, it still crashes your game.
2. Armour_Definitions.txt, armor_cell.gib, and icon_puncture.tga all suggest that the chassis's armors have pierce, concussion, and heat values. However, only the concussion value is used (as the hitpoints multiplier). The link between all three of these files is that the icon_puncture is used on the armor selection screen (armor_cell.gib) to represent the hitpoint multiplier which is actually the concussion value that was listed in Armour_Definitions.txt. The EXE supports the addition of the missing attributes to the armor selection screen but changing the values within the corresponding definitions has no effect on the bot itself (neither offense, defense, nor mobility). The data is saved inside of the bot file but none of it except the concussion seems to do anything. The fact that these attributes exist suggests that they either had or were trying to add these features but the code got re-purposing to save time (a common practice in programming).
