aside from it being a means of balancing, what's the real deal with the Stun damage from redlining?
where does it come from?
i don't have my books with me, as i am at work right now and i forgot the USB Device with the PDF's . .
could one not argue, that with sensory cutoff you could simply ignore the stun, as you have switched off all pain from that particular limb?
furthermore, if the stun damage is supposed to come from the stress the overclocked arm for example would inflict on the meaty torso, then what would happen to someone having both arms and the torso replaced?

is there anything regarding this?
aside from balancing issues mind you . .

Not unlike Essence loss, the "drain" caused by redlining is (meta) psychological in nature. Imagine it as a kind of reverse phantom pain. Having a limb that is super agile, super strong and super tough strains the self-awareness of your morphogenetic field, the ability that you are indeed still you, so to speak. Hence, the high essence loss caused by what could otherwise be considered a simple prosthetic. Only in this case, due to the constant presence of the unnaturally able limb, the morphogenetic field slowly adjusts to the unusual prowess.
If you redline however, you add a suddenness and, simultaneously, a further radical improvement of your physical abilities to the already present strain. Suddenly going from "super strong" to "twice as strong as super strong and suddenly able to haul a minivan at my enemies" breaks the willing suspension of disbelief that your mind has to maintain in order to accept the artificial limb, and causes a sort mental "backdraft" that manifests as stun damage.
...
In other words, I have no clue, sorry...

Well, it is from strain to the torso. Your arm isn't reinforced right for that level of power. When you have a cybertorso, you get a higher max strength, so it indirectly affects your strength when redlining-- you can have your base arm strength set even higher, which allows for even more redlining.

still does not explain why you get stun damage O.o
and higher base strength just means higher capacity for overclocking and thus higher damage potential to your target AND yourself due to the stun damage . .

1. Stun damage quickly turns into Physical damage once it stacks up.
2. Stun damage represents more than you think it does. Note that unarmed combat, by default, inflicts Stun damage. You can get cut and bloody very easily when you get punched.
3. The Stun damage from redlining represents your body and cyberlimbs straining from overuse. Sort of like how a superhero looks when he's overtaxing himself on a feat of strength. They can do it for a short amount of time, but the longer that strain goes, the bigger the impact it has until the body just can't take it anymore.

yes, yes, i know ^^
my problem is mainly with the size of the stun . .
on the lower end, you can handle the stun, but it does not help you to redline in most cases, as the effect would still be too small to make much of a difference . .
and in the range where you can REALLY do awesome things?
yeah, the stun overflows into physical, allmost instantly, and almost instantly fill up your physical monitor too . . so you're dead because you liftet a car. .

Eh? It's a linear increase of damage. For every +1 you go over the limit, the damage increases the exact same amount whether the original stats were 3 or 9. The only difference is the bigger, bulkier limbs built for work have the potential to go higher than more standard limbs (but there's no requirement to do so). So if that guy with a 3-limb wants to go to 6, he suffers just as much damage as the guy with a 9-limb going to 12. The guy with the 9-limb, however, has the potential to go as high as 18... but doing so completely overwhelms the rest of his body and he's going to breakdown in short order.

In other words, the body can handle the same amount of stress regardless of how powerful the limb itself is (since the body was reinforced just enough to handle the limb at its default rating). But the more powerful the limb, the more stress it can apply to your body when its overtaxed, and the more stress it applies the more damage it does. Pretty damn logical if you ask me.

hence, cyber-torso and sensory cut off . . if you can say:"nah, i don't wanna feel the fire burning on my arm" then why can't you say:"nah, i don't wanna feel ANY excertion from my cyarms on my cytorso" by not involving anything else from the body(lifting with the arms instead of the legs, maybe doing bench-press stuff)
obvious answer: balance, else our friend tank the troll would be bench-pressing vans and stuff like that . .
and yes, i do think it's kinda stupid that stun overflows into physical . . nothing like being full body cyborg replacement and getting knocked unconscious because your armor was so hard that you don't get any holes . .

It has little to do with the limbs itself and more to do with your overall body being stressed. Cybertorso's don't change that, they're just extra reinforcement that let you tweak your limbs that much more (and thus achieve the benefits of redlining without, well, redlining). "Sensory cut-off" isn't an option in the game to remove wound penalties; though if you had a Pain Editor or the like it would work just fine. The damage would still be there, however.

And why do you think it's stupid that stun turns into physical? If I sit there and just keep punching you in the face til you're hamburger... well... nuff said.

mainly for shooting stuff i think that's stupid . .
and the pain editor?
only works on stun . . the first round, you take maybe 15 stun damage, and can ignore it, if you have a stun track of 15 boxes . .
now next round if you don't stop, it's 15 boxes of physical right there, not even pain editor let'S you simply IGNORE that . . your character might not even feel it, but rules wise, it's still bad . . and if you happen to have a physical track of 18 boxes, in the third round you're dead or dieing with overflow of 12 boxes . .

Here's a question: what's the source of the Stun damage sustained by fatigue?

Annoyance.

Pretty much the same as redlining; it comes from overtaxing your system.

but how do i overtax a system that has nothing to do with my body any more? @.@
arms and torso are metal, more or less completely . .
i'd rather they had put one stress point per round of redlining on the redlined limb, up to a maximum of your physical monitor . . if that's full? limb says:"frag you, i'm taking a day off!"

Because your body includes your cybernetic limbs, too. They weren't designed to go over the norms you're redlining past. It's all abstract; damage represents a plethora of different things. It's the same reason you take damage when you get shot in the chest even though you have a cybertorso.

well, there WAS the precedent in SR3 with the cyber-head . . but mostly, i fully agree with you . . don't get me wrong on this please, it's just one of these moments where i have problems with the abstract damage rules x.x . .

... because the higher end stun damage from redlining represents you dislocating your arm (which might be metal, and you can turn off the pain from it, but your still taking the pain from your shoulder becoming disconnected), and the physical damage that spills over is you ripping your arm out of your socket (effectively). Just a partial example, because there is stress and trama and so on, but that's the general idea. (The cyberlimb is tied into the rest of your body after all. Which is why you need a reinforced torso for the burly limbs.)

Also, the wound penalties could be a result of degraded performance coming from the broken cyberlimb. It's not always just pain that causes a penalty; it could be anything.

Ever seen a hydraulic system bust open? I'm pretty sure cyberlimbs don't like it when that happens to them.

Recall that unless you are a brain in jar (CCU borg) your flesh and blood organs are still in there inside your cybertorso, providing your brain with nice stuff like blood, air, food, ect... (If you are a CCU, these rules don't apply to you). So even if you are nearly completely cybernetic, there are still flesh and blood parts to get messed up. And at the red-lining levels you are contemplating, its not hard to imagine at all. You quote what 15S? that means you had to be increasing your STR by at least 7 beyond whatever it's normaly designed to do, giving you and overall STR of at least 14. Your at ripping the doors of a tank level at that point. So... seen Ghost In the Shell? Something like that might happen...

Seriously though, when you red line a cyberlimb you (by definition) exceed its design operating parameters. So yeah, that augmented support beam in your cybertorso? The one that was specifically designed to keep your enhanced strength from deforming your cybertorso and bruising your precious, precious kidneys? Turns out they meant it when the put those limits in place, because beyond them that beam don't work so well any more. Push it to hard and something might break and rupture and organ, which could really ruin your day.

What Cain said about the cyberwear itself failing is another possible interpretation.