A mountain bike has thick tires and a sturdy frame. It can be heavy because it is made to withstand rough terrain. From personal experience, it is not the best style of bike to use in a short triathlon. It’s perfect if you want to ride for recreation or somewhere on a rugged path. You can get a quality mountain bike for a relatively cheap price. With gas prices so high it can be really convenient to have one in your garage if you feel like saving money and burning calories at the same time.