Trail-running shoes have bigger lugs for better grip while going over rocks, roots and uneven trail. The size and pattern of the lugs vary based on the type of terrain the shoes are designed for, so it’s best to match your shoes to the surface you’ll be running on. Also, the rubber is typically softer than what’s on road shoes so that it can grab and bend around obstacles in the trail for good grip. Because of the softer rubber, wearing trail-running shoes on the road, where they will regularly pound and rub on hard pavement, can wear the soles out more quickly than if you stick to the softer surface of a trail.