Mostly frame and tranny! A lawn tractor is designed for light work and mowing. Garden tractor is designed for ground engaging implements front and rear so frame is much heavier, tranny is stronger and can handle high weight loads. A lot of the lawn tractors have very good engines with a lot of horse power but if you stress the frame they will bend or collapse, and trannies will go bad when pulling more than slight loads or handling steep hills. By the way welcome to the forum from Titusville, Pennsylvania!