Both the Siemens and the CAF cars in Sacramento "hunt" but it's not the traditional hunting as much as the center truck banging around. The ride's actually not too bad over the end trucks. Not sure how the old VTA cars ride; so far, the few that are working are kept on the Blue Line which doesn't go where I'm normally headed. The VTA cars are very considerably bigger than the Siemens and the CAF, though - they are limited to 3-car trains which are about as long as the 4-car trains allowed of the other cars.

Not sure what causes the center truck "hunting" (using quotes because I'm not sure if it's really hunting or something else). It's not too bad until they get out on the PRW and kick the speed up into the 50+ mph range. Also, it seems to me to be worse on the newer concrete-tie track than on the older wood-tie track. Nobody's ever published about it that I have heard of. Bob2 seems to know of a lot of these studies - maybe he has some references.

Perhaps this is related to articulated joints with two carbodies sharing a truck/bogie? IIRC there were complaints about ride quality of the UA Turbotrain and some of the early streamliners, compared to conventional equipment, that were anecdotally laid on the light weight and articulated construction. Does anybody remember how those multi-unit articulated Daylight cars on SP rode?