Hi,

So this is my first carbon bike and I'm kinda confused about the torque values, for example. My Roubaix saddle clamp is specced at 6.2Nm, but preset torque wrench comes in single decimal torque value like 6Nm, is that okay?

Also, I'm surprised the saddle clamp for CG-R is rated at 13.5Nm, my Ocarina Torque Wrench only goes up to 10Nm, is it okay if I clamp the saddle up to 10Nm?

Thanks

Both are maximum torque specs that were originally called out in inch pounds (55 and 120, respectively) and converted to Newton meters. Your wrenches are both under the maximum torque spec, so you're not in too much danger of breaking anything from over tightening. I'd use carbon paste in the seat tube. If the saddle creaks at the clamp, I'd search for a torque wrench that maxes out at 15-16 N-m.

I agree with Darth up til the recommendation using a 15-16 N-m wrench on a saddle clamp specced at 6.2 N-m. (I may be confused about this: the OP states that his saddle clamp is specced at 6.2 N-m, but is rated at 13.5 N-m). A couple of things about torque:
1) The idea is not necessarily to get the right torque, it's to get the right tension on the bolt. This stretches the bolt a bit so that it retains its clamping force in use.
2) Typically, the amount of stretch is a significant amount of the available elastic stress. That is, torquing to spec stretches 'em pretty near the point of plastic deformation
3) To get the proper bolt tension, the amount of torque needed varies depending upon thread and face condition, and lubricant (or locker) on threads
4) These variations mean that the torque spec is approximate. One significant digit. So 6.0 and 6.2 are practically the same.
5) For super-accurate tensioning, you measure the bolt shank length before and after tightening.

Point 2 is why I may be confused. If the torque spec of a bolt is 6.2 N-m, tightening to 13.5 N-m will typically deform the bolt. Also, there's a lot of bolts on bikes that are set up to torque to 6 N-m. This allows (for example) me to care one t-wrench in my toolbag to tighten handlebars and seatpost clamp both.

Carbon construction is optimized, and brackets and such don't have the same safety margin as the same bracket on a carbon frame. Soooo...
--> Use assembly paste
--> Torque to stated spec (6.0 N-m) will be fine.

If I couldn't get the saddle to stop squeaking with paste and torque to spec, I'd take it back to the dealer and ask what gives. More than doubling the torque might pull the bracket off the frame, destroy the frame, and kill the warranty.

Again, to the original question: a 6.0 N-m wrench will be fine (especially with assembly paste).

For the technically minded, a German engineer wrote about fasteners here. Recommended.

It's not a matter of creaking, but of the saddle clamp rotating out of position

if you don't tighten the **** out of the single-bolt assembly.

I helped someone with that out on the road just the other week.

Not a great design, but it is light.

Thanks for the explanation - I don't have a Roubaix. Still not certain how the bolt is rated over 10 N-m and they tell you to torque it to 6.2 N-m.

I rode for so long with a Campy Nuovo Record seatpost and a Brooks Professional saddle, so everything these days seems light to me.

I highly recommend "Carroll Smith’s Nuts, Bolts, Fasteners and Plumbing Handbook" if you want to really understand bolted joints and fasteners.

I think that the 6.2 nm is for the seatpost clamp, & the other is for the saddle bolt.

Agree, ds. It's a little expensive now, though. Here, on Amazon. I also suspect the info is a little dated, as at the time of publishing, carbon fiber was not used on the race cars that Smith was so expert in.

A humorous anecdote. Smith had several books with similar titles. "Prepare to Win". "Design to Win". "Engineer to Win". And "Tune to Win". When he wrote the fastener book, his first suggested title was "Screw to Win". The publisher steered him in a different direction, I guess.

Love this sub-forum.

Reread the OP.

Yes. Very nice torque wrenches aren't much more accurate than +/- .2 Nm at that level, and +/- 1.2 is more likely.

Maybe, maybe not.

My Nitto S65 didn't hold its adjustment until I cranked it up to 16 Nm . OTOH Campagnolo C-Record (and the 95-97 SP10-RE, which is either a round C-Record post or unfluted Super Record) posts stay parked with a lot less.

I guess I'm clueless about what CG-R is.

Specialized Cobble Gobbler flexible seapost.

So what saddle clamp does the OP have on his Roubaix that only allows 6.2nM? Wait.. the OP seems to be talking about his first carbon bike, so there is only one bike being discussed?

Hello all, thanks for the replies and yes, the photo attached by Drew is the CG-R and only 1 bike is discussed at the moment

The 6.2Nm is the seat post clamp whereas the saddle clamp is 13.5Nm. I guess the manufacturers specified torque value have a safety range? Since torque wrenches tolerances differ?

Thanks, Drew (and Sy, and OP). The different specs make sense now. Two different bolts.

I take it from the comments that the CG-R is a good seatpost, but is hard to get tightened?

Can't speak to the CG-R on comfort, but most Specialized seat posts have the same clamp these days, including my Allez Sprint (shared with the 1st gen Venge), and you have to tighten the F* out of it to keep the saddle from tilting. I have an adjustable torque wrench and I had to put 12nm into it before it would stay in place. Was a little disconcerting as I have a carbon railed Brooks and I was really worried about damaging the rails.

Darth_Firebolt,

Good observation,,, Being fairly new to this great forum I've been amazed at many OP that replies are way off point. Appears just the first few lines in the post were read and that seemed enough for some to regurgitate long drawn out opinions. (Must be a cold winter up north.)

My mom always taught me to 'chew all my food properly' before swallowing.

But everything is fun to read and always something can be extracted for my knowledge base storage.

Not sure of the science behind it.. but I'd hazard to guess that the amount of torque req'd is somewhat dependent on the surface area of the clamp portion that is compressing against the saddle's rails. A clamp that spreads the compression over a larger platform area, has a different ability to clamp (for a given torque on the bolt) than a clamp where the compression is confined to smaller clamp area. Likewise, a smaller-area clamp type, is focusing the compression to a smaller area obviously, perhaps making it more difficult (or unnecessary) to torque as much without damage to the rails. ie. smaller clamp = more biting force? Somewhat a PSI thing..

Ignoring the rails for a bit... Basically what the big S has done with their seat posts is put two cones on either side of a round hole. You have to torque it up that hight to get enough pressure on the cones to create enough friction to keep the saddle from rotating up or down. I like the idea, position infinitely adjustable and you don't have to do the whole loosen one screw, tighten another dance.

I'm sure the actual PSI on the rails is much lower as a lot of that is going to be applied to the interface with the seat post, but when you go from a two bolt system that works just fine at like 5Nm, having to torque a bolt down to 12-13Nm just seems scary.