Seatpost

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A "plain" seatpost (silver) connects the saddle to the frame (red).

A microadjust seatpost (black) of a Trek Fuel 90 mountain bike.

A bicycle seatpost or seatpin is an tube that extends upwards from the bicycle frame to the saddle. The amount that it extends out of the frame can usually be adjusted, and there is usually a mark that indicates the minimum insertion (or maximum extension). Seatposts can be made of steel, aluminum, titanium, or carbon fiber.

Seatpost generally clamp onto saddle rails.

1 Sizes
2 Types
3 Maintainence
4 References
5 External links

[edit] Sizes

The size of the seatpost is dependent upon the internal dimensions of the seat tube of the bicycle frame. They come in various diameters, lengths and offsets. Offset is the distance between the centerline of the seatpost tube, and the centerline of the clamp area. Shims are often available to adapt a too-small seatpost to a too-large seat tube.

[edit] Diameters

Diameters range from 22 mm to 32 mm. 27.2 is a common size for road bicycles. 25.4 mm (1 in) is a common size for BMX bikes. Documented sizes are almost always a multiple of 0.2mm and include: 22.0, 22.2, 23.8, 24.0, 25.0, 25.4, 25.8, 26.0, 26.2, 26.4, 26.6, 26.8, 27.0, 27.2, 27.4, 27.8, 28.0, 28.6, 29.4, 29.6, 29.8, 30.0, 30.4, 30.8, 30.9, 31.4, 31.6, 31.8, 32.

[edit] Length

Lengths range from 250 mm to 400 mm. Mountain bike seatposts tend to be longer than road bicycle seatposts.

[edit] Offset

Offset can range from 0 mm to 25 mm.

[edit] Types

[edit] Plain

This type, usually found on older bikes, less expensive bikes, or kids bikes, consists of a tube which may decrease in diameter for the last inch or so (2.54 cm) and a separate clamping mechanism at the top. One bolt tightens the clamp to the rest of the seat post and to the saddle rails at the same time.

[edit] Micro-adjustible

This is the most common type found on bicycles today. They can be divided into two types; ones which can adjust the saddle angle continuously, and ones in which the saddle angle can only be adjusted to a certain number of positions.

[edit] Time trial

Some modern time trial bicycle frames are made from one piece of molded carbon fiber with an integrated seatpost that is cut to length depending upon the rider. The advantage is that it is lighter, can be molded into an aerodynamic shape, and removes the need to clamp an irregular tube shape. The disadvantage of this setup is that the seatpost height is not as adjustable. There is usually 2-3 centimeters of adjustment with the clamping device.

[edit] Suspension

Suspension seatposts allow the seat to move up and down with either a telescoping or parallelogram mechanism and incorporate a spring, an elastomer, or compressed air and possibly a damper to insulate against bumps. The preload of the spring may be adjustable. These seatposts are most common on hybrid and mountain bikes. Suspension seatposts usually come in fewer diameters, and shims are more likely to be necessary.

[edit] Maintainence

Seatposts should be periodically removed from the frame, cleaned, greased and refitted to prevent seizure of the seatpost in the frame. This is particurly important with bikes which do not have mudguards (fenders) that are regularly ridden in wet conditions.

There is some controversy about whether to grease carbon seatposts or not. There does not yet appear to be a consensus.^[1]^[2]