There are a few people around the car business who don’t like old cars.

Partly because, they say, they like progress, and things that are new are obviously going to be superior to things that are old. But partly because, they say, new cars feel tight and rigid and precise, and old cars all feel the same: baggy and soft.

Now, I don’t buy into that theory, because many old cars are brilliant. But I do have a hint of understanding – if not sympathy – with their viewpoint on how loose old cars can feel. Bushes wear, which puts a bit of slack into the steering and suspension, dampers can tire, and older cars weren’t usually built to the same levels of torsional rigidity as modern ones.

It’s their body stiffness I’m most curious about. Yes, I know I should get out more. Lots of torsional stiffness, or rigidity, is a good thing. A strong structure means it’s easier to get the suspension working well from it. Anything above, say, 30,000Nm/degree is apparently as stiff as you need a new car to be. At that point, you can tune suspension largely how you please. Race teams like to go a lot stiffer again, but the cost and weight involved in doing the same on a road car are prohibitive.

But I wonder if torsional rigidity, like dampers and bushes, fades over time. As metal gradually fatigues through constant use, does, say, a 20-year-old car that had a 20,000Nm/degree twisting stiffness when it rolled out of the factory only have 15,000Nm/degree now? Or less? Or does it stay the same?