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PostPosted: Wed Mar 30, 2011 6:10 pm 
Retro Guru
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Joined: Mon Mar 28, 2011 9:29 pm
Posts: 1877
Location: Somerset
Eddie King wrote:
highlandsflyer wrote:
Be very aware that recommended torques can be exceeded if they were recommended dry.

Thanks....this was why I asked the question...have no previous experience with carbon but have a very good idea of what my face could end up like if they fail....

Please could you explain your comment i.e. at the moment they were assembled dry...but if I use the recommended Fibre paste how does that change the equation ?

And lubricating the bolts, if less torque is required to overcome the friction in the threads then more force is applied stretching the bolt/clamping the bars. Common sense shouts to me: as little torque as possible to stop the bars moving. With multiple bolt bar clamps, torque the bolts a little before moving on to the next finishing with an even overall torque.

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PostPosted: Wed Mar 30, 2011 8:32 pm 
98+ BoTM Winner / Gold Trader
98+ BoTM Winner / Gold Trader
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Joined: Wed Aug 15, 2007 7:29 pm
Posts: 1648
Location: Netherlands
The thruth is in this thread, but in bits and bobs. Please note that stems clamp the bar with the aid of bolts and the higher purpose of torque settings is to put an upper limit on the clamping force exerted on the bars. Ultimately it prevents crushing of the carbon bars by overdoing it, but also lesser over-stressing will shorten the life of your precious bar.

The term "dry" when used for torque settings refers to the thread of the bolts and the boltholes. When you grease or lubricate bolt threads to the point that this reduces friction the net outcome is you will get more clamping force on the bars for the same torque applied.
So lubricating threads is really "overdoing it" for clamping the bars if the design is for "dry" torque. But do note that a small amount of lubricant between the bolt head and the washer or stem plate does help achieving a nice smooth action when torquing the bolts (just don't spill it on the threads).

The carbon mounting pastes refered to are to be applied in the contact area of carbon bars and stem parts. The purpose of these pastes is to increase friction between the bar and stem. More friction means less clamping force is needed to stop the bars slipping in the stem (or a seatpost in the frame for that matter).

So it is easy:
Mounting paste increaes friction to prevent slip and reduce the force needed
Torque settings serve to limit clamping force and protect bars & posts
Lubricating threads increases clamping force compared to dry

And I agree with a comment made above that the 5Nm Torque is more than adequate to achieve a solid stem-bar interface. In fact when the above simple principles are observed less than 5 will do fine also for Clydesdale riders like me.


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PostPosted: Thu Mar 31, 2011 7:39 pm 
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Joined: Mon Jan 11, 2010 2:32 pm
Posts: 658
Location: Near enough to be nearby are a star :D Everything I wanted to know explained in a concise and helpful manner

Thankyou once again to everyone who has contributed to teaching me a bit more

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