How do I keep my seat from tilting back? When I first got this bike, I got the saddle adjusted almost perfectly.  Recently it slipped back (so that the nose sticks up).  I loosened the bolt under the saddle, tilted the saddle back into the proper position, tightened the bolt up, and within a week the nose had tilted back up. Did the same thing again, but cranked the bolt even tighter; still happened.

I noticed that there's visible "scarring" or scraping on the top of the seat tube where the clamp that holds the saddle (not sure the proper term for those pieces) grabs onto the tube.

This is a 2009 Surly Long Haul Trucker (touring style bike; equipped like a commuter) with the stock seatpost (pretty sure it's 27.2mm.  No real branding on the seat post).  I'm a fairly heavy rider (near 250 pounds) and I do sometimes ride over some pretty rough stuff, so I suspect that might be part of the problem.

So far I'm seeing maybe 3 options:


Get a hex tool with more leverage and tighten that thing down even more
Some sort of super glue or epoxy (or maybe just a bit of old innertube?) to keep the seatpost from sliding back
Replace the seatpost (and clamp assembly, of course).  Except I don't know what to replace it with that wouldn't just get the same problem again...


Update: Pics: (sorry, phone pics, but I think they're workable)

First: overall picture, very careful to take the picture close to level.  Top tube has just a teensy amount of slant, almost level.


Closer in (you can see some of the scarring on the seatpost):


Attempt at closer-in picture of scarring after disassembly, but can't focus close with this camera:


Here's the saddle itself, which has no bending, no visible damage to the rails, etc.:


Here's the actual pieces of the "clamp".  On the right is the bottom piece that sits on top of the seatpost and under the seat rails, there's matching "scarring" at the points that touch the seatpost. On the left is the top piece that goes on top of the rails. On top is the bolt that goes through everything from the bottom (with a curved sort of washer thing that fits into a matching curved area on the seatpost).  The opposite side of the "bottom piece" basically looks just like the visible side of the "top piece", and the opposite side of the "top piece" is boring.


Update 2: Used a hex tool with a longer arm (more leverage), removed the bolt, greased it up and tightened it as much as possible, not worrying about damaging the already damaged seatpost further. The grease helps to allow a bit more tightening. This held up for a couple months but eventually seat started sliding back again.

Final solution: Thomson Elite seatpost, specifically the shorter model with a setback in silver ordered through my LBS. (they had black in stock but decided I was willing to wait an extra week to get silver) It's a two-bolt design that seems to be the top-end for seatposts that don't slip.  I considered a Salsa two-bolt seatpost that was a less expensive, but it didn't seem to be as heavy-duty.  I also considered a Nitto S-83 which is a two-bolt seatpost about the same price as the Thomson and has more of the classic touring look to it, but the Thomson seemed to be a bit better engineered and I like the markings on the Thomson that help you keep the same adjustment.
The problem is that there is only one bolt holding the seat at the angle you want.  Put enough torque on the back of the saddle and can overcome the friction that's holding the seat in place.

A few options:


Tighten up that bolt as much as you dare (but you've already tried that).
Increase the friction between the seat post and the bottom of the seat clamp -- either scuff it up or use some carbon assembly paste (ask your LBS, I've used it to keep my seat post from sliding down).
Switch to a seat post that uses a two-bolt design to hold the seat in place.  This is what my current and previous bikes used, one bolt pulls the nose down and the other tilt the seat back.  Get enough tension on the two and your seat stays right where you want it to.