Road Cycling - Seat Post Clamps and Carbon Fibre Seat Posts

I want to adjust the height of my seat post, but it is carbon fibre and I'm wondering how tight the clamp should be without damaging the seat post. Is there a way of determining correct tightness? How can you tell if you've damaged the seatpost?

Ross

You really should have a torque wrench for this type of stuff. A torque wrench is just a wrench that either has a dial or click (depending on the type of wrench you have) to tell you how tight you tightening something.

You can get a beam type wrench which has a dial on it or you can get a clicker type which will click when you've reached the desired torque.

I have the clicker type which ran me about $60 US and it has been invaluable. With all the different carbon, aluminum and titanium parts on bikes these days it's really crucial to get the proper torque on everything without over tightening.

Campagnolo suggest a setting of 10nm (or 88in lb) for the seatpost binder on their carbon post.

Tom

Thanks. I think I will buy a torque wrench, since they seem useful things to have, if expensive.

At the top of the seatpost it says 22Nm, which seems a little high compared to the 10Nm you quote for the Campag post. Perhaps the 22Nm relates to the saddle clamp rather than the seat post clamp (?). I think I may have to make a trip to the LBS to find out.

Ross

Yes, 22Nm is for the saddle rail clamp.

Also note, the beam type wrenches are a lot cheaper. They run $15 to $30 US. They're not as nice to use as the clicker type but they work fine.

Tom

Thanks, Tom. It's interesting that Campag are able to quote a torque figure, but when I emailed Deda to get a figure from them, this was their response:


Because there are so many possible seat post clamp designs and
specifications, it is not possible to recommend meaningful torque specs. An
integral clamp requires different torque than an external clamp; steel is
different from aluminum; a 5mm pinch bolt is different from a 6mm. The rule
of thumb is: use the least amount of clamping force that will keep the
saddle from twisting.

Ross

Where can you get a small torque wrench which clicks? I've only seen the really large ones...kinda difficult to work with on small bike parts.

Where can you get a small torque wrench which clicks? I've only seen the really large ones...kinda difficult to work with on small bike parts. You could buy an UltraSPARC-II CPU module for a Sun Enterprise server. :D I got a really nice torque wrench with the CPU module that's supposed to be used to tighten down the bolts to mount the processor onto the CPU board. Unfortunately, it's preset at 6 in-lbs and the allen-key is permanently fixed. :D

While the torque spec given by Campy may work well for their product, the answer given by the Deda folks is probably more realistic. While there is probably some amount of 'posterior coverage' present in Deda's answer, the fact is that you want to use as little clamping force as you can get away with to secure a CF seatpost. On my bike the seapost collar is pretty slim, and I would guess that probably only the top 1/4" of the seat tube is actually gripping the post with any meaningful amount of force. Initially I just tightened it down with what I though was insufficient torque and marked the post insertion point with a little dot of paint and then checked it after every ride. A few rides with a 5 mm Allen wrench taught me how much I need to tighten it to prevent the post from creeping down into the seat tube. Another good idea is to deburr and taper the very top of the interior of the seat tube with some sandpaper so that when the clamp is tightened there is not a very sharp pinch point at the top of the seat tube.

Where can you get a small torque wrench which clicks? I've only seen the really large ones...kinda difficult to work with on small bike parts.

I don't know how small you want but mine is a Craftsman that I got from Sears.

Here is a link (http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=00944593000)

Tom

On a related topic, I was thinking about getting a CF post, but how do I get the grease out of the seat tube? its in there pretty far, I'd imagine. I don't really want degreaser running into the bottom bracket of my frame, so how do I do it?

On a related topic, I was thinking about getting a CF post, but how do I get the grease out of the seat tube? its in there pretty far, I'd imagine. I don't really want degreaser running into the bottom bracket of my frame, so how do I do it?

Real long screwdriver and a rag,you'll get most of it.

On a related topic, I was thinking about getting a CF post, but how do I get the grease out of the seat tube? its in there pretty far, I'd imagine. I don't really want degreaser running into the bottom bracket of my frame, so how do I do it?
Assuming you have water bottle bosses on your seat tube, turn the bike upside down and spray the degreaser in via one of those holes. Otherwise, the aforementioned screwdriver and a rag will work just fine.