Tech Help question: Saddle Clamping Issue

Equipment
1

I am going to show my old number 1 bike a bit of tenderness this weekend as it is now serving as the daily commuter and has suffered for it. Before I do that I would like to dip into the collective wisdom on a particular issue I seem to be having with it: The saddle clamping.

The bike is a 2011 Cervelo RS… Soooooo comfy, especially with 28mms. Running 25s ATM because of the winter fenders/mudguards. Anyway it came with a Fizik Airone flexwing which I finally had to replace last year. After a rather protracted and painful search years ago I finally landed on a perch that my boney old arse could manage: The Fabric scoop. So once the Arione died that was the last bike to transition to the scoop. So it went on the middle of last year. Now it seems to be struggling to stay clamped. First incident was when I rode Flanders in September and seat dropped going up the Patterberg. Ho hum I thought; it was just an oversight in the torque. But it wasn’t gradually over the course of a couple of weeks I begin to notice that I am perching more and more on the nose of the saddle. Then lo and behold the witness marks are all the way back again. So I tap it forward and ratchet up the clamping torque once more. And the cycle begins again. As I like a forward position and probably should run with no layback it is obvious now looking at my little saddle bag. In the correct position this thing sits up. When the saddle has drifted back it lays flat.

The saddle post is the stock 3T Doric(?) which is a CF tube and (I think…magnet test this weekend) steel clamp head: standard two bolt cradle design.

So I could go with the beer can shims but what should I be attentive of when I disassemble it on Saturday? I am think of checking the rail cups on the clamps (rather than the cradle) for alignment and if they are steel and misaligned ‘persuading’ them back to a tighter radius. Other than that I am kinda stumped…

2

I seem to remember these posts being well known for slipping and creaking. A cheap replacement would probably save you some time, hassle and give you some peace of mind.

If you’re reaching the correct torque then shims won’t make any difference. You could try something like electrical tape on the rails to stop the slipping

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6

What are the saddle rails made off? I had an issue once where they were painted, and the paint had come off, creating slack for the saddle to move. And once it starts moving it often works itself lose.

Also if its metal rails in metal clamp, just up the torque a bit. If it’s carbon, use friction paste!

7

A few thoughts:

  • A little clear coat may be a ‘cleaner’ looking solution than taping round your rails. It’ll add a little extra to the rail’s diameter, and also a soft layer for the clamp to bite into. Feel free to rough it up with something like 100 or 75 grit sand paper.

  • Nobody’s mentioned friction paste (carbon grip paste). I always use this on my rails and pretty much everywhere apart from steerer tube.

  • Finally, have you bolted the seat clamp to somewhere near the max permitted?

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9

Not sure if I’m mis-understanding, but even on metal surfaces, these grip pastes are useful. They also help prevent metal from seizing (reacting) with other surafces. If you’re not using grip paste, that would be my first tip to try before modding anything! Technically it’s designed for carbon products, so you can bolt them down at a lower torque, but its function is the same regardless - it will increase friction. So get some paste, put a fine coat on your rail and clamp and bolt down to your usual torque. Metal on metal should be fine at a nice high torque like 6 or 7nm as long as that doesn’t exceed any listed max torques on your components.

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10

Or to stripped bolts. Check the threads?

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