@Stoneboro Branch posted:Yes; in two rail O scale a tight radius is considered to be about 40”. That translates to an 80” diameter circle; just a tad under 7 feet. Atlas O Scale SW’s can negotiate maybe a 36” radius if the track’s real nice and you lay in a transition curve. Forget about road power at that radius. Turnbacks are space eaters in two rail!!
I beg to differ. In designing an industrial area on my layout I tested Atlas SWs for minimum radius. The SW8 will negotiate a 17" radius curve but you need about 24" to couple a 40 foot car and 23" to couple a 34 foot tank car. I ended up with 26" radius for better reliability. My Iron Horse Models (Precision Scale) SW1 needs 22 inches or the universal joints become disconnected.
Real EMD SW series locos were designed for 100 foot minimum radius (25" in O scale).
From the Southern Pacific SW1500 operators manual:
"Truck swing limits single unit curve negotiation to a 60 degree or 100 ft. radius curve.
Two units coupled are limited by footboard clearance to a 38 degree or 154 ft. radius curve.
Locomotive coupled to a 50 ft. car is limited by coupler swing to a 40 degree or 146 ft. radius curve."
