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I wanted to know what the torque specification for this saddle (Brooks C13) would be. There is no torque spec/limit information on the Brooks website for this saddle. The concern is that the rails are made from carbon and would possibly have a different torque specification as compared to the steel rails on other models.

Pictures of the Seat Post

Seat Post with two bolts at the back with a two part clamp on top

Picture with old saddle with Alloy Rails

Seat post clamp with steel rails

Pictures of the Brooks C13 Carbon Rails with the clamp,

misaligned rail 3

misaligned rail 2

misaligned rails 1

2 Answers 2

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The torque spec for mounting a carbon railed saddle is not normally different from a metal-railed saddle. However, if the clamp the seatpost uses to attach to the saddle rails is not compatible with ovalized carbon rails and one simply torques the seatpost to rails clamp up to spec, damage can occur.

Carbon railed seats do require one to be careful as to the type attachment employed by the seatpost. This is driven by the fact the rails are carbon and if damaged/cracked/crushed it cannot be repaired AND that the rails on most (all?) carbon saddles do not have a round cross-section but actually an oval one. And the Brooks C13 Carbon is no different.

From the Brooks website, the spec on the rails for the C13 Carbon are: Rail: 7x9 mm Carbon Braided. 7x9 is oval, whereas metal rails (titanium, steel, other alloys, etc.) are round (7mm typically).

The Brooks website is silent on seatpost compatibility with ovalized carbon rails. At least I could not find anything.

Fizik (saddles), however, has been more prudent in communicating about seatpost compatibility with their carbon railed saddles (most of theirs are 7x9 mm as well). Fizik may have seen some early rail failures due to seatpost designs that caused stresses in the rails that created the failures. The current guidance Fizik gives is "Before installation, verify compatibility with your seatpost manufacturer between saddle rails and the seatpost itself. Many seatpost manufacturers provide different clamping solutions to assure full compatibility."

Less than a year ago, they offered more detail (no longer available on Fizik website):

Q: Is my seatpost compatible with your carbon braided rail saddles?

A: Most seatposts currently on the market are compatible with our 7x9mm carbon rails. As a guide: all those fixing the saddle from the top to the bottom. (But the ones that are not compatible, are typically the types that fix the saddle from the sides.)

There are 5 types of seatpost clamps represented:

Type A: Single Bolt Top-to-Bottom clamp

Type B: Twin Bolt (Front/Rear) Top-to-Bottom clamp

Type C: Twin Bolt (Right/Left) Top-to-Bottom clamp

Type D: Side-to-Side clamp (single bolt)

Type E: Hinged Rotational Clamp

Type A, B, & C are typically COMPATIBLE with 7x9 mm saddle rails.

If your seatpost is compatible, it still is prudent to be sure that any seat rail clamp you use is free of sharp edges that could gouge and damage the carbon.

Finally, there was a Bike Exchange question that is related to this aspect from a few years ago: Oval carbon saddle rails compatibility

Hope this information can help prevent damage if your seatpost is not compatible.

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    Thank you for your detailed answer! The saddle did arrive and says that the torque I need to use is 12NM. I have a VNT Elements seat post with what seems to be a Twin Bolt with two bolts at the back of the seatpost. I have attached some pictures to the thread. My old saddle had steel rails that seemed to fit better. The carbon rails on the brooks seem to be a little closer together. If I go ahead and tighten the rails on this seat post, will I break the carbon rails or is this by design? Commented Sep 26, 2022 at 19:01
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    @ChasingLakshmi Thanks for the pics. I think saddle clamp torque specs are usually expressed as this is the maximum you should tighten to. The clamp may hold the saddle at lower torque. You could edit your concern about the Brooks' rail spacing into your original post. It does look a bit odd. Does it tighten properly? Does your seatpost manufacturer specify that there's a separate clamp for carbon rails? My Thomson carbon post has a top-bottom clamp, and unlike most of those designs there's a specific clamp for carbon rails.
    – Weiwen Ng
    Commented Sep 26, 2022 at 20:41
  • @ChasingLakshmi You are welcome and Welcome to Bike Exchange (BE) as well! I have a carbon-railed saddle handy and I checked to see how much movement the rails would have to widen them, and it is pretty stiff. There is a little movement, but a bit of force is needed. I cannot tell you from my experience on this concern. You could create another question on this as a separate topic from this one (torque spec). That is, one on the rails not as wide as the seatpost (use the great pictures you have already obtained). There are probably others on BE than have this experience to share and help.
    – Ted Hohl
    Commented Sep 26, 2022 at 20:41
  • @ChasingLakshmi And finally, take the BE tour when you get time: bicycles.stackexchange.com/tour
    – Ted Hohl
    Commented Sep 26, 2022 at 20:42
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The torque spec will be determined by your seatpost. Some convert torque to saddle rail clamping force more efficiently than others. For most 2-bolt infinite adjust seatposts, 6-8Nm is a good starting point. Don't worry about it too much, as carbon saddle rails are usually plenty strong.

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  • The saddle just arrived and the torque spec on the saddle seems to be 12NM. The rails however seem to closer together than the rails on the old saddle... Is this a manufacturing defect or by design? Commented Sep 26, 2022 at 19:09
  • @ChasingLakshmi No offense, but your seatpost looks fairly cheap. It might be the seatpost which is out of spec. A little bit of misalignment should be fine, since the saddle is designed to flex in use anyways.
    – MaplePanda
    Commented Sep 27, 2022 at 2:07

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