Effects of Body Mass

[Flyndaran]

That would give me 12 HP on the dot with my normalized strength of probably 11 and slight pudge, that comes out quite nicely.
But there must be some variation. Biology is never that predictable.

[whswhs]

Originally Posted by Flyndaran

That would give me 12 HP on the dot with my normalized strength of probably 11 and slight pudge, that comes out quite nicely.
But there must be some variation. Biology is never that predictable.

What does "predictable" mean? If you mean that you can't predict one real, physical trait exactly from another real, physical traits—say, body surface area from body mass, or brain mass from body mass—well, yes, I'm right with you. But HP are not a real, physical trait. They're a game stat and nothing more. There is no real, objective physical trait that measures what HP are used to represent. So it's perfectly reasonable to define HP in terms of some physical trait. It's not an independent measurement of a different but correlated variable; it's a mathematical transformation of an already measured variable.

Bill Stoddard

[Flyndaran]

Hit points have realistic effects with regards to injury. Predictable in that they can be fixed to specific numbers with zero variability.
I stand by my statement that biology is inherently fuzzy. Two people with identical masses can have different degrees of ability to handle injury outside of Health based death checks.

[whswhs]

Originally Posted by Flyndaran

Hit points have realistic effects with regards to injury. Predictable in that they can be fixed to specific numbers with zero variability.
I stand by my statement that biology is inherently fuzzy. Two people with identical masses can have different degrees of ability to handle injury outside of Health based death checks.

There is no realistic physical variable that measures how badly someone is injured. Both the hit points of a character and the damage rolled for a weapon are purely game mechanical numbers.

Bill Stoddard

[Flyndaran]

Originally Posted by whswhs

There is no realistic physical variable that measures how badly someone is injured. Both the hit points of a character and the damage rolled for a weapon are purely game mechanical numbers.

Bill Stoddard

Two people of equal mass will suffer differently from otherwise identical injurious impacts.
Ignoring that just for precision of gaming numbers seems odd to me. But your game, your rules.

[Varyon]

Originally Posted by whswhs

I use weight = (HP/2)^3, which gives 125 lbs. for 10 HP, and 167 lbs. for 11 HP. I don't quite like having weight be a multiple of BL, because BL varies as an area (cross sectional area of limbs) but weight should vary as a volume.

Bill Stoddard

Personally, I feel 8xBL covers human ranges a bit better. When creating new species - or adapting real ones to GURPS - I'd probably go with 2*(average weight)^(1/3), then figure out an appropriate Lifting ST for an average specimen, and figure out what multiple of BL their average weight is closest to. That allows other species to have a more narrow range of weights for their HP. It may or may not be realistic, but I think it works as a much more gameable setup.

Originally Posted by Flyndaran

Hit points have realistic effects with regards to injury. Predictable in that they can be fixed to specific numbers with zero variability.
I stand by my statement that biology is inherently fuzzy. Two people with identical masses can have different degrees of ability to handle injury outside of Health based death checks.

Agreed, and this is precisely why I'd allow HP to vary from what it "should" be according to mass.


Alright, from the looks of things, I didn't miss any factors in my initial estimate, so I think it's about time to start looking at price.

For Grappling, high body weight imposes a penalty on others who use mass-based moves on you. Each +1 is comparable to a half-level of Improved Parry (one skill), or [2.5]. However, this virtual Improved Parry is passive, only applies to mass-based moves, and corresponds to a difficulty in friendlies moving you around. That implies maybe something more akin to [2] or lower - and as you can accomplish much the same by simply carrying around more weight (which can be shed much more rapidly than inherent weight) and your foe's Training Bonus offsets the penalty, I'd be more inclined to go with [1] per +1. That's somewhere around [1] per additional BL (based on HP, not ST) pounds, or [-1] per BL fewer pounds, or +12.5% mass.

For Knockback, this is something like IT:DR or Vulnerability to Crushing, albeit with a No Wounding modifier. For Collisions, this is increased or decreased Striking ST, with a Slams Only modifier. For falls, this is IT:DR or Vulnerability to damage from falling. Altogether, I think it's relatively fair to call this a Feature and move on.

Blowthrough is again a case of IT:DR or Vulnerability, this time against Piercing damage and with the caveat that it only comes into play if there's overpenetration involved. It would be [15] or [-15] without that caveat, maybe somewhere around [10] or [-10] with it, for a modifier of 1.5. We'll go with [+10] for 1.5, [+20] for 2. This is for +50% mass, implying something like [+1] per +5% mass.

Carrying Capacity is Payload (External -50%), or [1] per -BL/5 lb to body mass. We'll simply reverse this for heavier characters. That's [+1] per +2.5% mass. This is built as a stacked Alternate Ability to the Athletics effect, below, making it [1] per -12.5%, but [-1] per +2.5%.

The Athletics effect is arguably something like a [10] Talent. However, it doesn't improve learning speed or give any sort of reaction bonus, and it doesn't allow for carrying anything outside of your Payload, above. Altogether, that probably justifies around [5] per +1, so [5] for -BL, [10] for -2xBL, [15] for -5xBL (first +1 - achievable by running around naked - is free). We'll simply reverse the signs for being heavy (this arguably gives back more points than it should, as it's like an Anti-Talent but less restrictive, but it's probably close enough). That's [+5] for +12.5%, [+10] for +25%, and [+15] for +62.5%.
For the Move portion, it's probably easiest to assume a base Move of 5. Every +1 from above corresponds to a +1 to Move - as each of the above is [+5] and the change to Move is the same, that simply doubles the above numbers - [+10] for +12.5%, [+20] for +25%, and [+30] for +62.5%.

Armor is probably the most difficult to figure out. It's something like the Cheaper Gear Perk combined with a proportional Payload that is External and Armor Only. Ugh. The easiest way to figure it out is to assume average mass (just like we assumed average Move, above). We'll further assume the Cheaper Gear Perk is negated by the fact your character has lower MaxDR for any given material.
We'll modify the equation from Pyramid #3/52 slightly - as average mass is 160 lb, we'll use (weight/160)^(2/3). This works out to around -10% to armor mass per -BL to character mass. An "average" armor loadout is probably something like Light Encumbrance, or 2xBL. Because the armor is also easier for allies/mounts to transport, we'll just go with our Payload being [1] per BL/5 lb, just like External alone, which is, conveniently, 10% armor mass. That means the modification to armor is worth [+1] per +12.5% mass, to a maximum of 5 levels of the trait.


Now, the above values alternate between 5% and 12.5%, which have a common multiple of 25%, so we'll use that. Grappling works out to [2] per +25% mass, [-2] per -25%. Blowthrough works out to [5] per -25% mass, [-5] per +25% mass. Carrying Capacity works out to [2] per -25% mass, [-10] per +25% mass. Athletics is a bit more complex - [20] for -25% mass, but only [30] for -62.5% mass (reverse signs for higher mass). Armor works out to [2] per -25% mass, [-2] per +25% mass.

Leaving out Athletics - which should only come into play at breakpoints - this means every +25% mass is [-15], every -25% mass is [7]. This works out to [-1] for every +1.67% mass, [1] for every -3.57% mass. EDIT: Throwing Athletics back in (it should still be counted below the first breakpoint, as it increases the amount you can carry and get the "stark naked" boost), it adds in another [-1] for every +1.25% mass or [1] for every -1.25% mass up to +25%, after which point it is [-1] for every +3.75% mass or [1] for every -3.75% mass.


A final point that I actually did miss in my first post was consumption. This would be optional, but you could easily apply the guidelines from Bio-Tech to scale the amount of food and water lighter/heavier characters must consume. As with armor, this shouldn't be able to exceed the increase/reduction resulting from a +1 to SM, which is -50% ([3]) at 30% weight, +50% ([-5]) at 125% or so weight.

[Not another shrubbery]

Originally Posted by McAllister

Can you purchase HP-less mass? HP with a special -100% modifier that only counts towards calculating mass-based effects?

Weight has been treated as essentially a Feature for a while. If it mattered, I suppose you could always calculate a virtual HP level based on that.

[Flyndaran]

Originally Posted by Not another shrubbery

Weight has been treated as essentially a Feature for a while. If it mattered, I suppose you could always calculate a virtual HP level based on that.

It's a feature for most Gurps situations, but can kill your character in others. Being strong enough to carry an extra 100 pounds is nothing on earth in Gurps. But on a 1.5 G world, suddenly you have a lot more weight to lug around.

[Varyon]

It has occurred to me that setting default ([0]) body mass based on HP, ST, or any other trait is inherently flawed. Rather, it seems more appropriate to have an absolute mass as the default, and any variance from that either costs or gives points. Yes, this does mean being a cat is now worth more points, and being an elephant is worth less. For campaigns where the default assumption isn't a human (or equivalent), feel free to set the default mass differently.

For most campaigns, a default mass of 160 lb* works well. Typically, to determine a character's weight, use 8x(HP^2)/5 (you may vary this as you see fit, of course). For Grappling, every +20 lb (+12.5%) is [1], every -20 lb is [-1]. For Blowthrough, every +8 lb (+5%) is [-1], every -8 lb is [1]. For Carrying Capacity, every +4 lb (+2.5%) is [-1], every -20 lb is [1]. For Athletics/Move, every +2 lb (+1.25%) is [-1], every -2 lb is [1], up to +40 lb (+25%), after which point every +6 lb (+3.75%) is [-1], every -6 lb is [1]. For Armor/Clothing, every +20 lb is [-1], every -20 lb is [1]. [EDIT]A raw change per +n lb is inappropriate. Rather, this should be handled as sufficient Lifting ST to negate the change, with the Limitation "Only for carrying armor/gear," and reversed. Factoring in price should be handled as doubling to value of the trait, based on Cast Iron Stomach being -50% for "price only." My next post has the relevant equation; note this eyeballs the "Only for carrying armor/gear" Limitation as around -16.7% (I originally had it as -20%, but felt an end multiplier of 5 in the equation worked better than 4.8)[/EDIT]. For Consumption, every +~26.7 lb (+~16.7%) is [-1], every -26.7 lb is [+1].

Overall, this means - leaving aside Athletics/Move for the moment - every +80 lb (+50%) is (4-10-20-4-3)=[-33], every -80 lb is (-4+10+4+4-3)=[11]. That means every +~2.4 lb (+~1.5%) is [-1], every -~7.3 lb (-~4.5%) is [1]. Athletics/Move, from above ([+1] per +2 lb until a change of 40 lb, after which point it's [+1] per +6 lb), is added to this.

Things can be broken up. Grappling effects, Knockback, and Slams/Falls (note Knockback, Slams, and Falls combine into a Feature) should always use your character's actual weight, but for anything else a "virtual weight" is acceptable - a human-sized 1 ton robot might be able to wear armor as though it only weighed 160 lb. Carrying Capacity and Athletics/Move should always both use the same virtual weight, however (for simplicity, simply ignoring both of these effects may be ideal; consumption is also probably a good idea to ignore, just grab Reduced Consumption or Increased Consumption if desired).

Another thing to consider are toxins. For simplicity, the size of a toxic dose should scale based on body weight, such that you need twice as much to affect a target that weighs twice as much as usual. This is either IT:DR or Vulnerability to Toxins, which is something like [+20] (Occasional), and a +2 to HT for the same, arguably around [+3], for a doubling/halving of body weight. That is, +160 lb (+100%) is [23], -80 lb (-50%) is [-23]. Of course, +320 lb (+200%) is only [35] or so, and -107 lb (-67%) is [-35]. The easiest thing to do here is just to keep in mind that a different weight than default justifies IT:DR or Vulnerability to Toxins (at [10] or [-10] per level; every +1 SSR to weight justifies a level), optionally with Resistant/Susceptible to Poison available as well.


Body mass does interact, after a fashion, with SM. For the most part, any mass increase due to SM should be handled as noted above. There are two volume effects that should also be kept in mind, however. First, one's virtual mass for purposes of armor/clothing cannot go beyond the average mass for the next SM up or down (for SM 0, this is +100 lb). Secondly, once SM comes into play Consumption shouldn't be ignored any longer - it should use the guidelines from Bio-Tech, but rather than being a Feature should be approximated using Reduced/Increased Consumption. As I outlined here, the non-mass-based effects of SM more or less work out as Features unless you are using a houserule that adjusts wounding modifiers based on SM. If that's the case, take the mass-based effects from here and tack on [25] for every +1 to SM, [-25] for every -1 to SM.

*Yes, I'm aware 160 lb is a weight, not a mass. If you'd like, think of it as "a mass that weighs 160 lb in 1G." Of course, in different gravities, Grappling and Falls end up being a bit different, but as Grappling favors higher-weight characters and Falls penalize them, call that a wash.

[Andreas]

Originally Posted by Varyon

someone with higher HP than their mass indicates is someone who is particularly resilient, for example. Here's what I have so far.

Blowthrough: Someone who is thin and wiry simply isn't going to absorb as much of the energy of a bullet passing through them as some hulking brute. While this makes the latter a more effective meatshield - he can absorb more damage - the fact he takes more damage in the process is problematic. Net Advantage for being lighter.

Wheter this is appropriate depends a lot on what the extra resilience from more hp represents. If it is just being better able to deal with an equally sized injury, then this is approprite. However if it represents the body being harder to injure in the first place (for example someone with low HP for his mass might have bones that break easily, skin and muscles that tear easily etc.), then blowthrough should scale with HP rather than mass.

I tend to think that the second option is the more natural interpretation of what HP different from what your mass would indicate represent. Being better able to deal with injury of the same size is already represented by HT and traits such as Unkillable 1.