I have a 2015 Specialized Roubaix SL4 Disc with a CG-R seatpost, and recently bought a Fizik Vento Argo R1 short-nose saddle for it.

Knowing it has ovalised carbon rails and not the standard 7 mm alloy rails, I ordered a different clamp for 7x9mm rails. I was dismayed to discover, however, that the Vento Argo R1 actually has 7x10mm rails.

Will this work? Is it safe? Is there another clamp I can put on a CG-R seat-post which is specifically meant for the rails on the Fizik saddle?

  • I just found myself in the same situation. Any update OP?
    – Rob
    Commented Sep 15, 2023 at 19:31

1 Answer 1


I’m going to attempt an answer since someone else had this problem.

Some seatposts clamp the rails from the top and bottom. If you know what a Thomson seatpost looks like, those are to to bottom. Some seatposts clamp the rails from the sides. The CG-R is one of those.

Carbon rails are ovalized, with 9 or 10mm being the vertical dimension. Clamps that go top down should be fine with either height. I am assuming the heights are actually different. Given the 1mm difference in nominal dimensions, I would assume this is the case. Note, however, that everyone uses the 31.8mm handlebar clamp standard, but Deda (at one point?) reported their diameter as 31.7mm. I think the actual dimension may have been 31.75mm nominal, but most people rounded up.

I would assume that rails clamping from the side need to explicitly state compatibility with 9mm or 10mm rails. So, if I were in the OP’s position, I would consider using a different seatpost, not that there are a whole lot of direct alternatives to the CG-R. The Canyon VLCS seatpost has a similar aim to the CG-R, but it’s been reported as out of stock for a long time.

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