Athearn Impack Cars wheel issues

[Wildcatfootball]

I have a few strings of Athearn's old impack cars, but they all roll pretty bad... I took out a few wheel sets, and I've never seen such small wheels in HO before. Where can I get metal replacements for such small wheels and what diameter are they any way? 30? 28?

 

[jbaakko]

28" and yes, North West Short Line (NWSL) makes metal ones that can be used as replacements.