I'm a newbie to model railroading and chose n scale because space is limited. The rear coupler on my atlas engine derails the car it is pulling when it goes around a 9 inch radius atlas turn by pushing the coupler on the car to the outside of the curve. This causes the outside wheel to ride up and out of the track. The cars will not do this to each other but my engine will always do it to the first car it is pulling. What can be done? (asides from using 11 inch radius turns) Your help would be greatly appreciated.