peripatetic

What do you call the clamp that holds the saddle rails to the seatpost? Is it the 'saddle clamp'? And does anyone know if I can replace one of the older style ones that tightens on both sides with one that tightens with the single bolt on the underside? A link would be appreciated, thanks!

Retro Grouch 

Yup, the different seatpost designs are pretty much interchangable but you have to replace the whole seatpost. The thing to be careful of is the diameter. The diameter of your existing seat post is normally stamped near the bottom of the seat post.

The two bolt clamps are more than just an older design. Lots of riders like them because they make it possible to adjust the tilt of your saddle more precisely than the one bolt models.

peripatetic

Great information, thanks R-Grouch!

MichaelW

The old design of seatpost clamp had a horizontal bolt that could be tightened on each side. The only advantage of these was that you ccould remove the whole clamp from the post, flip it around and mount the saddle forward of the post for a time-trialling/triathalon style (this is really old-school british TT racing from the 1950s).
Otherwise, they are heavy and coarse to tune.
Std ones have a single vertical bolt.
A modern alternative is a 2-bolt design: The 2 bolts are forward and aft of the post and allow fine-tuning of the tilt. This is my favourite type.

Saddle rails are all pretty standard so you can switch clamp style. Do get the correct diameter otherwise you can damage the frame. It should move in the frame like a piston.
You can spend a lot of lightweight posts but unless the rest of the bike is lightweight , you wont notice any difference.

peripatetic

Do all seatposts come with both 1- and 2-bolt designs, or are they each only available on specific seatposts? (I recently realized that the tilt on my saddle was too far forward, and I was getting really sore wrists from riding.)

MichaelW

Every seatpost seems to be an individual design, not part of a series.
The 1 and 2 bolt designs are totally different.
One important factor in setting up your saddle in the correct position is the layback of the clamp from the post. The 1 bolt designs have the clamp offset behind the post, some with more layback than others. The 2-bolt ones have the clamp inline with the post. If you run out of saddle rail adjustment, then you need a post with a different layback.

Retro Grouch 

Most seatposts come as either a 1 bolt or a 2 bolt design. They're not interchangable so you have to make do with what you have or else replace the whole seatpost. There's also a third design that clamps the bike seat rails in a circular clamp that can be rotated in the seatpost clamp.