Turn your bike into a parent/child tandem with Trek's Mountain Train 241. This high-quality one-speed trailer bike is made of high-tensile steel for durability. It attaches easily to your seatpost and the boom arm folds for easy storage and portability. The Mountain Train also comes with an adjustable stem so you can get the handlebar position just right. And, it has a 24-inch aluminum wheel for easy pedaling, too.