Mountain bikes are typically ridden on mountain trails, fire roads, logging roads, and other unpaved trails. These types of terrain commonly include rocks, washouts, ruts, loose sand, loose gravel, roots, and steep slopes. Mountain bikes are built to handle this terrain and the obstacles that are found in it, like logs, vertical drop offs, and small boulders. Mountain bikes, therefore, are more sturdily constructed than regular bicycles, have larger knobby tires, more powerful brakes, and the lower gear ratios needed for steep grades with poor traction.