QUOTE: Originally posted by ndbprr OK, the circumference of a circle (the distance you would walk if you walked all the way aaround the circle) is the diameter of the circle x pi or 3.14. So a circle one foot accross would be 1x3.14 or 3.14 feet. A two foot circle would be 2x 3.14 or 6.28 feet. So the bigger the radius the bigger the outside of the circle. Now I am assuming that N is roughly 1/2 the sixe of HO and you need 2" clearance when the train goes around the circle once so the bigger you can make the diameter the longer the distance and the lower the grade. So if you can use 24" radius in N that = a 4' diameter x 3.14 which would yield a circle 12.56' in length. Mutiply that x 12 for inckes and you have a circle that is 150.72" in length that needs to rise 2" to clear the original level. If I divide 2" / 150.72 it gives a garde of 1.32% which is a grade that shoudn't affect many engines or train lengths. If I go down to 18" radius the grade increase to 1.8% still an ok grade. much below that you are probably asking for problems as the drag may topple equipment. Now as far as your curvature problem. You have something wrong in the way your flextrack is laid. Either vertical variances or you aren't maintaining a constant curve. try making your self a template. Ribbon rail used to make track gauges of various radii to place between the rails to hold it constant until spiked down. Any machine shop could make you one easily or anybody with a CAD program could draw one for you that you make out of styrene or aluminum.