Seatposts Guide
A seatpost is the part that connects your saddle to your bicycle frame. The seatpost is designed to fit perfectly inside the seat tube of the bike, there are various sizes available, the size must match the seat tube exactly. The top of the seatpost has an included part known as the saddle clamp that clamps around the rails of the saddle and allows forward and back adjustment of the saddle along with saddle angle adjustment.
You might see there are various sizes of seatpost available, for example, 27.2 x 400.
This refers to the diameter of the seatpost and the overall length. The diameter must be exactly as intended for your bike, if you are unsure what size you need, it should be stamped or written on the old post. If the size is not shown, the manufacturer's specifications should show what size is needed.
The length is often more than needed, but check the total length of your existing seatpost to check what length is needed. Some riders with small frames might need to cut the post shorter to lower the seat to the correct height.
Please note the minimum insertion mark that shows the minimum amount of post that must remain inside the bike for safety reasons.
Rigid Seatposts
A rigid seatpost is the tube that slides up and down inside the seat tube of the frame allowing you to adjust the height of the saddle for different leg lengths. A rigid post is the lightest type of seat post and is seen on the majority of bikes. There are various sizes available to suit different frames and can be made from aluminium, titanium or carbon fibre.
Seatposts can be available in different lengths to suit riders who need a lot or not so much extending out of the frame. The top section near the saddle clamp can also have a setback, where the saddle clamp is offset to the back of the bike or they can be straight to suit the different fit and reach preferences.
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Dropper Seatposts
Dropper seat posts let you adjust the height of the saddle easily while riding. A relatively new addition from the world of mountain biking, the dropper seatpost is now seen as an essential addition to any mountain bike. Having the saddle at the correct height for pedalling efficiency is great until the terrain changes and you need to drop the saddle out of the way so you can move your body weight around without the saddle being in the way.
A cable or hydraulic hose feeds from the post up to a remote actuator on the handlebars. Some frames support internal routing for this cable/hose, known as internal or stealth routing. Other frames only support external routing, there are also externally routed dropper posts for these frames. The standard seatpost diameters apply, along with the different lengths. Dropper posts are also available in different amounts of drop to cater for different leg lengths.
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Suspension Seatposts
Suspension seatposts can look like dropper posts but instead of dropping out of the way with the press of a lever, they remain at maximum extension until you ride over a bump. A suspension seatpost with have a certain amount of travel to tame a bumpy road and make cycling more comfortable. They are sprung by air, coil or with an elastomer.
The same variables apply to suspension posts as to other types. They are available in different diameters to suit different frames, and different lengths to suit different leg length.
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Seat Clamps
The seat clamp is the part that secures the seatpost in the frame to stop it from moving. They are made in different sizes to suit different frames. The size of seat clamp is not the same as the size of the seatpost. The seat clamp will always be a larger diameter than the seatpost to cater for the thickness of the frame.
There are quick-release seat clamps that give tool-free adjustment. Standard bolted seat clamps and even ones that include mounts for a rear rack or a guide for an externally routed dropper seatpost.
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