Taking into account that the vast majority of seatposts are the same in looks and functionality, there are a few things that one needs to consider before buying one. More specifically, it is essential to look at the diameter, material and the clamp type. Most of the modern frames fit either a 27.2mm diameter or a 31.6mm (oversized) seat post. The arguments for each of these sizes are that an oversized seaptops is said to add stiffness and strength for optimum power transfer and resistance to bending, while a narrower seatpost is more comfortable over rough terrain. If you have a frame which requires an oversized seatpost, you can always use shims and fit the regular 27.2mm.