By the way those "spaghetti" .89 torsion bars are what Chrysler engineers (you know, the ones that designed the rest of his car) specified for a Dart with a big block. I think they will do just fine.
That argument only has any merit if your car is 100% factory. Same skinny bias ply tires, same horsepower, ALL of it. And it still assumes the factory engineers didn’t make any mistakes (they did) or that the bean counters didn’t change things for sales and marketing, which they also did. The factories do not make perfect cars, they generally make the cheapest car they think they can sell without getting sued.
Even the standard all season radials people run like the BFG T/A’s have significantly more grip than the factory bias ply’s did. And of course if you run wider, taller tires than factory that changes everything too. And add more horsepower.
Most modern cars, and I’m talking basic commuters not performance cars, have a wheel rate around 200 lbs/in give or take a bit based on weight. A lot of them also have sway bars in addition to that. That’s basically a 1” torsion bar on these cars.
