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Your math is pretty close, Jim, and your logic correct. No way a conventional circular helix can utilize 22" radius without having 2.6% or more for a ruling grade. The thickness of the track used ( Atlas is about 3/16" thick overall ), plus the total thickness of the roadbed used, must be added to 3" to give a logical clearance, and one that pretty well conforms to NMRA standard in HO. So, to keep the 22" radius, keep the grade to 2.6%,and use Atlas flextrack, you have to use roadbed no thicker than 5/16", with the track fastened directly to it. If you want to use cork roadbed over 1/2" plywood, you'll need to go to a 2.8% grade. (I factored the circle down on these calculations to 43 1/4" diameter, since the inside rail is the determinate radius for vertical clearance). I have one spot in my layout where I 'squeeze' passenger cars around a 22" radius, but it is easy to get to, and fairly level. I would be reluctant to do so on a 2.6% grade or where any track is hidden, but it may be possible if track is perfectly laid. Compliments of the Season & best regards / Mike
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