[LouisVuitton]

So while I'm wrenching on my own carbon parts I see most of my parts list a torque setting. For example, my seatpost has a marking for 8nm. When I see these torque settings listed, does that mean 8nm is the MAX that I want to tighten it down or is that the recommended torque setting I should tighten all the way to?

 

[wim]

A torque value marking generally refers to maximum torque. The manufacturer thinks the part will perform its task without damage to itself or damaging a mating part if tightened to the torque marking value. But since the manufacturer has no control over customer work habits and the nature of a mating part from a different manufacturer (grease/no grease, friction paste or not, accuracy of wrench, mating part tolerances), these markings are really more of a conservative recommendation than a hard-and-fast technical specification.

 

[FBinNY]

As Wim noted there are a number of unstated variables involved which affect the relevance of the torque values. On many components there's also the problem that the minimum torque required to do the job is unreasonably close to the maximum torque the parts can tolerate.

Use the torque as a guide, bolstered your experience, and try not to tighten any more than deeded to do the job.

 

[mymilkexpired]

I would advise to use friction compound designed for mating carbon parts.

 

[frdfandc]

You want to use that old german spec

Good-n-tight.

You don't have to reach the max spec thats listed, just tight enough to keep seatposts/bars/etc. from slipping. And with the added use of carbon paste, this will help reduce the required torque to keep things from slipping.

 

[sbindra]

So while I'm wrenching on my own carbon parts I see most of my parts list a torque setting. For example, my seatpost has a marking for 8nm. When I see these torque settings listed, does that mean 8nm is the MAX that I want to tighten it down or is that the recommended torque setting I should tighten all the way to?

There's also real world experience. I find that when installing a carbon seatpost, assuming I use carbon paste, 5nm to 6nm is enough to hold without slippage although my seat collar states 6.7nm max.

Ritchey recommends 5nm on their stems and sells a torque tool that tightens to exactly 5nm so I would imagine the actual tolerance is a bit higher, they just want you to use their tool. FSA's max on stems is 7.8nm. I set my torque wrench to 5.4nm or 5.8nm (those are the increments of my tool) and either setting is sufficient for seat collar and for all bolts on the stem.

 

[ultimobici]

There's also real world experience. I find that when installing a carbon seatpost, assuming I use carbon paste, 5nm to 6nm is enough to hold without slippage although my seat collar states 6.7nm max.

Ritchey recommends 5nm on their stems and sells a torque tool that tightens to exactly 5nm so I would imagine the actual tolerance is a bit higher, they just want you to use their tool. FSA's max on stems is 7.8nm. I set my torque wrench to 5.4nm or 5.8nm (those are the increments of my tool) and either setting is sufficient for seat collar and for all bolts on the stem.

Are you sure that the torque settings aren't 6-7nm not 6.7nm or 7-8nm rather than 7.8nm?

 

[sbindra]

Are you sure that the torque settings aren't 6-7nm not 6.7nm or 7-8nm rather than 7.8nm?

No - the seat collar actually states on it MAX 6.7NM. It is not a range, for max the manufacturer gives an actual number. At these settings, the difference between 5nm and 6nm is significant, almost 18%

 

[thesmokingman]

I always thought that torque numbers were not up to interpretation?

 

[Darryl W]

For carbon parts I always use this:
http://sheldonbrown.com/tork-grip.html

 

[Guppie58]

bikes usually have specific settings listed right on the components now. At least the last couple bikes I bought did. Really takes the guess work out of it.

 

[frdfandc]

I always thought that torque numbers were not up to interpretation?

Torque numbers are usually described 2 ways. A range - like from 10 Nm to 14 Nm, or a Max like a seat post clamp at 5Nm.

But if you can get a seat post to be secure at 4 Nm and not slip at all, would you continue to torque it to 5 Nm, even though the clamp says Max 5Nm?

 

[thesmokingman]

Torque numbers are usually described 2 ways. A range - like from 10 Nm to 14 Nm, or a Max like a seat post clamp at 5Nm.

But if you can get a seat post to be secure at 4 Nm and not slip at all, would you continue to torque it to 5 Nm, even though the clamp says Max 5Nm?

I would follow whatever the spec says just like I do when working on my car. I wouldn't take the risk of a fastener coming loose just because I had "felt" it was tight enough.

 

[frdfandc]

I would follow whatever the spec says just like I do when working on my car. I wouldn't take the risk of a fastener coming loose just because I had "felt" it was tight enough.

You gotta use a little common sense in this sense. I know that its ironic, because common sense isn't common.

You aren't going to tighten lugnuts to just good enough, but a 8mm bolt that holds a window regulator into the door is going to be tight enough with a socket and ratchet. Not gong to bust out a torque wrench to do that.

 

[thesmokingman]

You gonna debate just to be contrarian? When a manufacturer specifies a torque spec, it means they want it at that spec. Not everything is specified, but when there is...

 

[Buckhead]

I tighten everything to around 4.5-5Nm and have not had any problems. I'm over 200lbs and haven't had any seat slippage or handlebar rotation.

Just my two cents...

 

[wim]

You gonna debate just to be contrarian? When a manufacturer specifies a torque spec, it means they want it at that spec. Not everything is specified, but when there is...

There's some truth to that, but sometimes you do need to deviate from that spec. When a manufacturer of, say, seat post clamps has "5 Nm" printed on his clamp, he's telling you that his clamp should hold your seat post and that the clamp screw will not break if you tighten the clamp screw to 5 Nm. But since the clamp manufacturer has no way of knowing the brand and model of your bike and your seat post, his torque specification is more of an educated guess than a proven number. In view of that, "tighten until it holds" is often the better way to go at this.

 

[saba]

my bmc has a 5nM and a 8nM setting on the seatpost clamp. I set the top to recommended 5 but dont go past 7nM on the lower bolt. Why? Cause you start to hear squeezing of the carbon at 7 and there is NO reason at all to go all the way up to 8. So torque settings are not absolute. I have had zero slippage at 7PM over many races and lots of bumps.

 

[wim]

my bmc has a 5nM and a 8nM setting on the seatpost clamp.

Well, that's the thing: with almost all bike "makers" really being no more than "bike assemblers" for shipment in a cardboard box, chances are good that clamping forces on mating components are rarely, if ever, established by testing. Another reason to go by feel rather than the number on a sub-contractor's part.

 

[ewitz]

my bmc has a 5nM and a 8nM setting on the seatpost clamp. I set the top to recommended 5 but dont go past 7nM on the lower bolt. Why? Cause you start to hear squeezing of the carbon at 7 and there is NO reason at all to go all the way up to 8. So torque settings are not absolute. I have had zero slippage at 7PM over many races and lots of bumps.

In this case I would not do this. Same as with torquing faceplate you want even pressure by torquing all the bolts to the same force to allow for even clamping force around the circumference so that no stress risers form.