that's a lot of info!! thank you!!
and yeah, I hear you about the stainless. ive NEVER worked with it at all. but I have a friend who is a major welder, self employed, and he has 2 big Grumman workhorses, and an F250 diesel worktruck, retired king county police truck, actually. 10mpg, lol... actually he says the HUGE Grumman workhorse, which, empty, weighs I would guess, over 10,000lbs, and LOADED with his tools and materials, over 18,000lbs, gets BETTER mpg than the F250 pickup truck. anyhow, im off track. he has told me, on MULTIPLE occasions, that stainless is VERY prone to rust, if you use the wrong wirebrush, <I already knew THAT>. or even if you just work mild steel in the same 18x20ft room, the airborne particles can ruin a major project that he spent thousands of dollars, and dozens of hours on. and he says he has just taken some of these major projects in the past, with a deadline ticking down just a day or two away, and chopped them up, and scrapped the whole thing, because it patina'd. same thing with aluminum. he has a bunch of old retired bedsheets and comforters, and he covers EVERYTHING, anytime he works mild steel in that room. so none of the aluminum or stainless gets "polluted".
but 4130 isn't stainless. stainless has like way more chromium. like 9-12 percent. chrome-moly <misleading name> only has like one percent chromium.
and 4130 is what they make great bumpers and rollbars from. cuz its lighter weight. well, in a sense its lighter, cuz you use less of it. also, another advantage most of these rollcage websites don't know, or at least don't mention, is that 4130 keeps a lot more strength after an impact. like, lets say you roll your car off a cliff, and into a big tree. and it rolls 3 full flips, and slams into the trunk of a big fir tree or maple, say like 8 foot diameter tree. well, mild steel will often be JUST as strong, on the FIRST impact. it will protect you, pound for pound of material, as the expensive 4130 rollbar. but then your car flips again and again, and slams into that tree. well, on the second impact, that same rollbar has like <just rough guesstimating again, here> 60% of its original strength, or integrity. say, like.... damn, its a hard guess, but lets say that, assuming the mounting points are literally INVINCIBLE for the sake of a simple calculation for me. well, lets say the rollbar can take the first impact, and LOOk to our naked eyes to be perfectly solid, and not even have ANY visible dent or damage at all. well, if it starts out at say.... 16,000lbs of capacity. <hard thing to measure in a tube structure, versus a simple rectangle billet>, well, that original 16,000, STILL looking like brand new to our eyes, is NOW worth about 10,000lbs of integrity. but the 4130, even though it is THINNER, is rated about twice as strong as the mild steel, pound for pound. and so, if we assume it started out as capable of taking a 16,000lb impact, NOW its only good for about 13,000 or 14,000lbs, for the second impact. then the 2nd roll happens, and you bounce off that rollbar again. well, now the mild steel tube is only worth about 6,000lbs. and the 4130 is maybe 10,000. both are probably noticeable deformed at this point. then it flips again, and the mild steel tube is worth... maybe like 1,500. I know that's a lot bigger drop, relative to the first drop. but keep in mind, its not just the metal itself, now, its SHAPE has been compromised. that convex or straight form, is now riddled with stress risers. think how fragile and weak an eggshell is, once its already been compromised.... egg=ultra strong. eggshell, extremely weak. in fact, to elaborate on that point, I raise chickens. free range, they just wander my entire yard at will, and lay their eggs in the bushes, blackberries or wherever they feel like. so I am well aware of how an egg works. typically, they INSTINCTIVELY know to somehow lay their eggs, smaller point UP. never on their side. sure, they might shift later on. but anyhow, even natures miracle shape, the birds egg, has strong sides and weaker sides. the LONG sides, a.k.a. the waist of the egg, is MUCH weaker than the top and bottom. its a much broader curve, and the unborn chicks instinctively peck at THAT specific part, when they are ready to be born. <also, they are pecking at the INSIDE of the curve, the concave form>. try punching your windshield from the inside or the outside. I guarantee you, you will shatter half the bones in your fist, if you try it from the OUTSIDE, the convex curve. but even as a 85lb wimpy 6th grader, I could easily punch out a windshield from the INSIDE....
where was I?
oh, okay, assuming you are still reading this long ramble... don't be too quick to add uneccessary weight to anything automotive, because theres more to gain from proper and efficient SHAPE than there is from just dumping more and more metal into it. everyone laughs at SMART fortwo cars? well, im not personally planning to BUY one, myself. but if you watch videos of the crash tests, that little smart car does BETTER in frontal impacts, than a ford explorer or a jeep grand Cherokee. with like, half the weight, or less. a rectangle is a CRAP shape. eggs or triangles are so so much better. and 20lbs of QUALITY steel is always stronger than 50lbs of recycled soup cans.