Dirt bikes and ATVs do not have many common features due to size, weight and use differences, but some similarities include disc brakes and electric fuel injection. The engine size and transmission system are always going to be larger on an ATV than a dirt bike because the machine is much larger and needs more power in order to perform.
Most ATVs have large engines usually between 350cc and 450cc. The ATVs can come with smaller or larger engines as well, but these are less common than the standard size. The tires are nothing alike, though both ATVs and dirt bikes have off-road style tires. An ATV has four tires, which can be anywhere between 14 inches wide up to 25 inches wide. The type of tread on the tire can go from smoother for sandy trails to highly textured for rougher terrain where riders need more traction.
Dirt bikes are much smaller than ATVs, which means that the engines are smaller, lighter and more compact. A common engine size for these bikes is 250cc. The tires are much smaller as well, but have the same kind of tread as ATV tires. Dirt bikes can go on most of the trails that ATVs can, though they do not have the weight to do some of the climbing some ATVs can do.