People often ask me where the main landing gear should be located when converting a trike gear model to taildragger layout. I have found that a good, simple rule of thumb is to locate the gear such that the model's tail can be raised 30 degrees from horizontal before it tries to nose over, if you fly off a grass strip. This method takes the height of the center of gravity into consideration, not just its fore and aft location. A high wing model, with higher center of gravity, thus needs its wheels located further ahead of the CG than those of a low wing model. If you normally fly from a paved strip, 20 degrees will do the job, and make the model less prone to ground loop. Landing gear location on a taildragger is always a compromise - further forward makes the model resist nosing over, but promotes ground looping. Further back reduces ground looping tendency, but increases the tendency to nose over.