Actually I believe the correct rule of thumb regarding determination of unsprung weight is only 50% of the tb is considered "unsprung". Think about it, half the bar is attached to the sprung chassis, and the other half to tb connector. Since the tb is uniform shaped, thats likely pretty accurate. In leaf springs and say shocks, the same rule of thumb is used, but likely is not as accurate since their masses are not uniformly spread out along their connecting axis.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
