Not sure if I'm describing that quite correctly in the title, so I took a quick video. Basically, the front wheels of the tanker car rotate as a pair along an invisible axis that's in between the wheels, whereas the rear wheels behave correctly.

https://drive.google.com/open?id=1U_ofIVhzrrAOW4OYTD0lD8fa4-HsHcYm

hah, that's a good one. I'll fix that tonight