This is new thread on an issue that was that getting slightly off topic in the original thread. Let's consider a slight variation of the Ehrenfest experiment. The fairly rigid carriages are all linked together by elastic couplings and are on a suitably highly banked track. As the velocity of the train increases, the elastic couplings get progressively more stretched putting a measurable strain on the carriages. At high enough velocity, the strain on the couplings get so high that they all snap. Once the couplings have snapped the stretching strain on the carriages vanishes and we end up with essentially the rod thought experiment I first proposed with no longitudinal strain parallel to the track, but there will of course be transverse strain as the carriages/ rods will of course be compressed down on to the track by the reaction force to the centripetal force exerted by the track. The transverse strain is not an issue here because I am only considering longitudinal length contraction. The Thomas rotation is also not an issue here, because the orientation of the carriages/ rods is maintained by the banked track. The key issue here is, can you in principle fit more carriages on the track when they are moving at relativistic velocities, than the number of carriages that will fit on the same track when they are at rest wrt the track?