Seat sliding back
 

I set my seat about in the center of the rails and tightened it as much as I could. As I rode it gradually slid back all the way to the point where the rails bend at the nose. Reset and retightened, same thing happened. Solution?

There is not a canned solution to every problem, and you don't indicate that you have tried to do anything but what did not work in the first place. Could be damaged threads, something interfering with the clamps or with the rails sitting properly. I think you need someone in person to check it.

New seatpost. better quality, expensive one.

when you take your bike to a BikeShop, they can see
the issue, and order a new part.

Maybe I should have clarified that this is a new seat. I didn't have this problem with the previous seat.

Yes, it is helpful when presenting a problem to specify anything that changed when the problem occurred. Answer is still pretty much the same, but you could try installing the old seat and if it still is OK carefully compare how the two look when mounted.

http://www.universalcycles.com/shopp...s.php?id=30551

It prevents seizing, and also has a gritty component that prevents slippage.
While advertised for CF, I've also used it on metal seatposts in metal frames to prevent slippage.

I just took the clamp apart, reseated everything, retightened, and tested. Within 3 miles the seat had again slipped back to its maximum position. The clamp bolt is tight and showing no signs of slippage. I'm wondering whether the rails of the seat are very slightly small for the clamp. Do rails have a standard size to fit all clamps?

However, the two halves of the clamp are not completely closed up. There is a slight space between the two halves at the outer edges. If the rails were too small I would expect the clamp to be closed up completely.

"However, the two halves of the clamp are not completely closed up. There is a slight space between the two halves at the outer edges."

Is there a space between the two halves where the clamping bolt is? My concern is that the bolt may not be exerting force on the seat rails but rather is just clamping the halves together. Is it possible that shimming the rails would cause them to be clamped tightly? Perhaps your seat rails are somewhat undersized, as you are wondering.

the rail diameter of the 2 saddles may be different..

measure and report data .
may need to buy a proper vernier dial/digital caliper ,
or visit a place that owns one.

With a razor knife and scissors, carefully make shims out of a beer can. If it works, then you know your problem. If you don't care then leave it permanent. Wrap your pieces around a phillips screwdriver for a jig. Must be beer can also because if you use a soda-pop can and tell your buddies of the fix you sound like a nerd! But if you use a beer can you can talk about football afterwords.

Yes, there is the expectable space of about 1/16" - 1/18". How do you shim the rails?

Assumptions, assumptions . . .
1. The world is male.
2. The world is young.
3. No one wants to be a nerd.

Hold on while I go visit my red-neck neighbors for a beer can.

Measuring the diameter of the rails is a good idea. If the new ones are smaller then the clamp probably is bottoming out.

What you need to do is 1st is look from the back of the saddle into the center area of the clamp where the bolt passes through. There should still be space between the top and bottom portions of the clamp. If not then the clamp is bottoming out before exerting full pressure on the rails. If that is the case you need to shim so that the clamp is forced apart more.

This is how I would make shims. I would call it shimming the clamp, but it comes to the same result. Remove the top bolt and clamp. Cut two narrow pieces of can twice as long as the clamp area on either side and about twice as wide. Be very careful with your fingers, as the pieces will be quite sharp. Fold each in 1/2 so that they are now the same length as the clamp area. Place each shim on the clamp and use a screwdriver shank to conform them to the curve of the clamp. Carefully place the saddle rails on top of the shims, replace the top portion of the clamp and the bolt, and tighten down the bolt.

I don't know of any single-bolt post that tightens the ability to to rock before tightening the rails enough that sliding would be impossible, even with greased rails. I suspect that the top plate is bottoming out on something (a misplaced washer) and preventing effective clamping on the rails. I'd take the post apart and make a rail sandwich with the clamping plated (no post or bolt) and look around for any parts making contact, or near contact. Likewise, I'd check that the bolt's thread is OK and it'll thread in well beyond the point it needs to with the clamp attached.

If I didn't spot an issue, and still had problems, Id find something about 1/6" or so thinner than the rails, maybe a piece of wooden dowel and see if the post can clamp that effectively on two sides. By now you should have spotted the issue, and made an adjustment, either shim the saddle rails, or used a traction compound to improve the grip.

IDK about either part (s)he's got . never mentioned..

With saddles you can see the rails open from the side ..
I found the Race Face Clamp brilliant,
there are 2 bolts ..1 clamps the rails from the sides,
2nd one holds the tilt angle.

other saddles, with stiff skirts on the sides Ala SI Turbo , SM Rolls
2 bolt from the bottom are nicer ..

if a Trad leather saddle, the original Campag seatposts were made for them..
2 bolt heads on the top are reachable with the wrench
by folding the leather sides up for the moment..
<C> wrench #771 was made to go on the brooks tension nut too
Z bend to reach the 10mm bolt heads on top of the post.

Look at the INNER edges too.

Are you emplying that your an old female that's a proud wine drinking Nerd with great neighbors?

I'm late to the party, but I had the same type of problem with a Giant Cypress I owned. As other people have said, the new seat probably has thinner rails. Inexpensive/free fix - use a piece of old tube to form a shim around the rails. Slightly costly fix - buy a new seat post.

Another fix using the existing seat post, assuming that there is enough metal there to do this safely, is that you could separate the top and bottom sections of the seat clamp and then file or sand the joining faces slightly. Just .125mm or so on each side could make a difference. Before you reinstall, make sure your mating surfaces meet flush. Also make sure your bolt hole isn't stripped and use some medium strength thread sealer to make sure that it stays tight.

I've taken this up with Selle SMP. I don't really understand their reply. I'm attaching a photo of my seat clamp. Is this not a standard clamp?

Their reply is, "The clamp is not like the SMP seat post recommendation because the clamp is an arc instead of being straight."

There is a diagram of the required clamp at http://www.albabici.com/selle/tech-i...smp-saddle.htm under "Seat post recommendations" halfway down the page. #3 says, "the clamps must be the same shape as the outside surface of the saddle frame, so that there is good coupling with a large contact surface (fig. 3)"

I honestly can't see the problem with my clamp. It has fit every other seat I've put on it. Selle SMP also suggets sanding or tape, but I don't get why this should be necessary.

Huh. This is a weird one. I've come across the odd seat that tiltled, but never one that slid...

That is very a common design of clamp, among many different designs. Selle's correspondence seems bogus; that crap about an arc makes no sense.

You say there's a small gap when you clamp the seat in it; there's also a small gap in your photos, presumably with the bolt done all the way up...

It would appear the rails of your new seat are a bit small for the clamp. I'd stick a bit of plasticine or something between the halves and see where it's fouling.

Act of trying to clamp it tighter is bending things, making the grip worse..

upgrade the whole seatpost to get a better clamp assembly.

Assumption much? Looks like there's enough metal there to me... and it doesn't seem shaped in a way that'd do that.

[QUOTE=Kimmo;14497321]
You say there's a small gap when you clamp the seat in it; there's also a small gap in your photos, presumably with the bolt done all the way up...

QUOTE]

No, the seat bolt is loose in that photo. It tightens up just fine, no slipping threads.

[QUOTE=SteamingAlong;14466821]Inexpensive/free fix - use a piece of old tube to form a shim around the rails. QUOTE]

Thanks, Steaming Along! Your solution worked! I always like a simple low-tech fix. Smart.