Healthy and active
Join Date: Mar 2007
Location: Caldwell, Idaho USA
Bikes: mid-60's Dunelt 10-speed, Specialized Allez Sport Tripple, Trek 7.2 FX
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I also have a carbon fiber seat post and like to stay within recommended torque specifications. My bike is a Specialized. I was able to download some technical service bulletins from their web site, including one on carbon seat posts. It included torque specifications. In the case of my seatpost, the recommendations were 40 to 55 inch pounds. Somewhere I saw higher figures for another seat post. There is a chart of torque specifications available for download at the Park Tool website
, but many of the figures are based on a particular manufacturer. Still, they give you a rough idea of where to start. You might check the web page for your bike's manufacturer for any technical service bulletins.
Even though I used the suggested torque, my seat post sometimes slipped downward while riding. I solved that by moving the mounting collar for a rear reflector down the seat post to sit directly above the seat tube and tightened it moderately. It provides enough assistance to keep the post from sliding.
Several times I have posted information about my homemade torque wrench. It works very well. It is a steel bar strong enough not to flex and a dial-indicator fisherman's scale. I made one end of the steel bar so it will receive my standard "L"-shaped Allen or hex keys. I checked the accuracy of the fisherman's scale and found it weighed six percent light, which would have resulted in too much torque. I shortened the distance of the bar by six percent from the nominal ten inches I had planned to compensate for the error. I also try to stay a little toward the low side of allowable range of torque, just to be safe. At a nominal ten inches in bar length, a five pound pull is 50 inch pounds.
Torque specifications always assume you put a drop of oil on the bolt before tightening.
And, my bike has an aluminum frame. I have read that aluminum and carbon can bind themselves together with moisture and time. One recommendation is to remove the seat post periodically and put it back into place. That calls for torquing it again.