when your going forward the back end has to follow the front around and follows a different path to the front wheels,so reducing how sharper corner you can go around(an obvious example to show you what i mean would be a long lorry,the trailer/back end drags behind and so it has to take a wider line around the corner to be able to get the back end round).in reverse when you steer you are really steering from the back(the front is now the back because your are reversing).this enables you to point the back of the car(which is now the front due to you reversing)where you want and the back no longer follows you around due to it now steering around the corner and not dragging behind hence now being able to go around sharp corners(this is why fork lift trucks etc steer from the rear).That probably sounds like jibberish but its hard to explain,ah well at least i tried.
