This video details my opinions on curves, grades and switches for G scale trains. My railroad features mostly mainline 1:29 scale trains with body-mounted Kadee couplers.
Operating long passenger cars and freight cars with body mount couplers can require some track strategies for best results. The biggest points to take away: Avoid grades over 2%, avoid curves tighter than 16ftdia (LGB R5), and avoid making S-curves!