What is the difference between these bachmann trucks with wheels
42534 & 42535 come without wheelsets
42536 & 42537 come without wheelsets
42534 Friction Bearing truck no wheels (https://shop.bachmanntrains.com/index.php?main_page=product_info&cPath=265_420&products_id=2758)
42535 Roller Bearing truck no wheels (https://shop.bachmanntrains.com/index.php?main_page=product_info&cPath=265_420&products_id=2759)
42536 Friction Bearing truck with wheels (https://shop.bachmanntrains.com/index.php?main_page=product_info&cPath=265_421&products_id=7382)
42537 Roller Bearing truck with wheels (https://shop.bachmanntrains.com/index.php?main_page=product_info&cPath=265_421&products_id=7383)