I have just done some calculations for my rise to the rear hill. The circumference of a circle is found by multipling 3.141 times the diameter. So a 15" radius would have a circumference of 94.2 inches (30x3.141). Thus the half circle length is 47.1 inches. Now the percent grade is: rise divided by distance. If the rise is 4" and the distance from the start of the rise is just the 1/2 circle then the grade would be 8.5% (4/47.1). Bad percent of grade for a normal train? What is the best grade for a normal train; diesel or steam?