Seatpost for carbon rails - unusual size

[deejayen]

I'm thinking about buying a saddle with 7x9mm carbon rails. My seatpost is 26.4mm, and an old Stronglight aero seatpost with single bolt.

Am I correct in thinking that this seatpost won't be compatible with carbon rails?

Are there any seatposts which would work? I thought USE and others made 25mm seatposts which I could use with a shim, but I think they're no longer available, or not very common.

[Karvalo]

I'm thinking about buying a saddle with 7x9mm carbon rails. My seatpost is 26.4mm, and an old Stronglight aero seatpost with single bolt.

Am I correct in thinking that this seatpost won't be compatible with carbon rails?

If it's a vertical bolt it'll be fine.

[deejayen]

Thanks, I think it is.

Do I have to check for anything else, such as edge shape of the clamping area etc?

[ms6073]

As long as the actual clamps do not have curved 'fingers' intended specifically for round rails, then there should not be any issues. Examples below include the clamp mechanism for the current Enve two bolt seat post which includes clamps for round and oval rails and hopefully it is plain to see that the clamp for round rails is not going conform well with 7x9 or 7x10 oval rails.

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[deejayen]

Thanks very much.

My seatpost is a lot older than that Enve! It's more like this:-



Would you still say it should be okay?

[ms6073]

I would not think that post would pose any issues for saddles with oval rails. I edited my previous post with an image that is more indicactive of the kind of clamp that I have found to be problematic with oval rails.

[Karvalo]

Thanks, I think it is.

Do I have to check for anything else, such as edge shape of the clamping area etc?

No, not really. To a vertical bolt seatpost clamp a 7x9 rail is identical to a 7x7 rail. The rail size specific clamps that ms posted about all have horizontal bolts.

[Nickldn]

Use a torque wrench and don't exceed the maximum safe clamping force stated on the carbon rails. Ignore the clamping force on the seatpost clamp if higher. You may need to use carbon paste.

[deejayen]

That's great - thanks very much!