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Bicycle Seat Posts

A Bicycle seat post typically comes in two different designs

  1. A steel or aluminum shaft tapered at one end, similar to a tent post. A separate clamp, washer and bolt system is used to attach the rails of bike saddle to this seatpost. Sliding it back and forth along the rails adjust its relative position to the handlebars. This is most often found on less expensive bicycles.


  2. The more modern version of a bicycle seat post combines the post and the saddle clamp into one unit
  3. . They come with either one or two bolts that clamp mated metal plates onto either side of the rails of your bicycle saddle. Typically the two bolt pattern has greater strength and accuracy when adjusting the front-rear position and the tilt.

Seat Post Clamps: Bike seat posts also require a seat post clamp. This is what holds the post at the right height within the bicycle frame. There are typically two styles. The one on the left is tightened with a wrench or allan key. The one on the right, my preference, uses a quick lock lever and can be adjusted quickly and without the use of any tools.

      
Post Composition:

  • steel: usually chromed for greater rust resistance
  • aluminum: great for weight but rigid and have to watch tightening up the aluminum screws... they can snap. And remember not all aluminum is created equal.. there is airplane grade and well, you know the stuff in the coke© tin.
  • titanium, great for weight & flexing on aggressive trails
  • carbon fiber seat posts.. carbon fiber is the newbie on the block as far as material science goes. Its structure has natural ability to dissipate vibration which of course is the benefit in using it for seatposts. It is NOT typically lighter than its aluminum cousin, but it does have greater production flexibility.

Weight: there is a wide range of weights, mostly depending on the size (both length & diameter), with or without suspension and composition (steel, aluminum etc), so difficult to cross reference without having all the details... and almost impossible to use this as a measuring stick of quality. A very thin aluminum post will be very light, but stand no chance to survive most aggressive mountain biking:

Typically 155-270grams

Seatpost Diameter: There is a very large range of seatpost diameters. Thus it is important to mate the diameter of the post to the specifications of the bike frame itself. Some of the posts coming from Europe can have as little as a .2mm difference in diameter, so it is best to go to a local bike shop that has either the frame spec's or a proper measuring tool to get you the right sized stem. If matched incorrectly you may have trouble tightening the seat post clamp sufficiently to prevent seat slippage.

Length: As with diameters, bicycle seat posts come in a wide range of lengths. The choice will partly depend on your frame design and how much height you need on the stem to adjust for your riding comfort. Typically a mountain bike seat post is between 350-400mm. The mountain frame is smaller so the post must be longer and typically more rugged. A road bike seat post is around 250mm. A road bike frame is larger so the post doesn't have to be quite as long to get the leg length you need.

It is important to note that all seatposts have a mark along the shaft to indicate the maximum extension of exposed shaft.. the balance of the stem is required to be inserted into the frame for overall clamping strength. Trust me.. don't go beyond that mark. I have actually snapped a seat post that I'd jacked too high!

A Bike Seat Post with Suspension: Gas, springs and elastomers are all used to provide some dampening abilities to the seat post. I'll add some more info what I get a few extra minutes.

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copyright Jan. 2007