i have two Bachmann starter sets that i am looking to upgrade. the cars seem nice and look good to me. i would like to upgrade to metal wheels. i purchased a pack of Proto 2000 33" wheels that the LHS said would fit. they do fit, but don't spin without a lot of effort. infact, it drags the wheels down the track. any idea as to what metal wheels i could buy to fit the Bachmann frieght cars? thanks.