Drag racers used tube axles and split the radius rods but they didn't go over bumps or around corners at speed street rods followed the old drag race design which was ok for straight line driving. you can end up with terrible handling and bump steer on the road they can point ypu in the wrong direction real quick . the same goes for the rear suspension
I.ve had hair pins break
the i beam can flex (twist from one end to the other. 4 bars make more sense on a street driven car