The GP40,35,38 , 50 F models are good diesel runners on 18"radius track . most of all the 4 wheel truck models will do well . the 6 wheel truck models the ones with -2 at the end of the model number do well on 22" radius but on 18" radius have a tendency to derail if the track is not laid well or a little rail height difference at the rail joiner's. don't get me wrong they will run on 18"r track but they like the bigger radius better . and watch your turnouts with short connectors and s-cerves .Bachmann makes really reliable diesels so have fun .