Question: Is it recommended to use carbon paste/assembly compound on carbon steerers or other carbon parts? From: Phillip
Answer: Carbon assembly paste is really helpful in preventing damage from over torqueing components. Tiny pieces of glass suspended in a gel help to increase friction at the component mating surfaces. This means that it takes less compressive force to hold the component in place.
On carbon stem and carbon road handlebar interfaces this is especially helpful due to the reach of the bars and the added leverage offered by the hoods. If a handlebar isn’t clamped securely it could slip in the clamp and cause you to go over the bars. We’ve found that with carbon paste applied to this interface you can typically set your torque wrench 20-30% below the recommended max torque value and still have a solid setup.
Seatposts are another great area to apply carbon paste. I especially like to use it on dropper posts because these take a huge amount of force every time the saddle is dropped. Plus, if seatpost clamps are overtorqued, the dropper post won’t function correctly and could even be damaged.
When it comes to carbon steerers there is little need for the additional friction that carbon paste provides, as it is very rare that anyone encounters a situation on a road bike where your front wheel is being pushed hard in a direction opposite to the direction you are turning the handlebars. The exception is during a crash. In this situation it’s better to have the stem slip on the steerer to lessen the amount of force transmitted to the steerer tube.
The other concern with applying carbon paste to steerer tubes is that the paste could make its way into the headset where it could grind down moving parts and possibly wear the steerer where the compression split ring interfaces with the steerer.
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