(This question came to me while I’m at work, so I don’t have y books available to double check this, but also don’t want to risk forgetting it as I transition from leaving work and dealing with everything else I have to this weekend. So apologies n advance if this has already been covered.)
There are at least a couple of places in ACKS where a rule has been made in respect to the type of armor worn. Barbarian class adventurers can only wear chain mail or lighter. The Running proficiency can only be used when wearing chain mail or lighter. If a player is wearing plate mail +3 should he be treated as if he’s wearing chain mail or lighter armor since the plate mail +3 does weigh less than regular chain mail?
I am not an Autarch, but my ruling would be based on the type of the armor and not the actual weight.
Each type of armor has its own ways in which you support its weight and its own ways in which it impairs your movement, regardless of the actual weight of the armor.
Based on Alex’s comment in http://www.autarch.co/forum/swashbuckling-and-armor-encumbrance-0, I would expect it to be based on form. As he says, though, it’s your game - do what’s fun for you.
Thanks for pointing that out, I had not seen that remark. I don’t want to see thieves using chain mail +2. That may not make sense in some ways given that some magical chain or plate might actually weigh less, but at some point I have to acknowledge balance over verisimilitude. (Something I very rarely do.)
Even if they don’t weigh much, chain may still be noisy, plate may interfere with certain movements (and be noisy), etc. I’ve always interpreted class armor restrictions as being based on the physical form of the armor, not on how much it weighs.
In general it’s based on the form, not the weight, but as always feel free to modify the rules as needed for your campaign!