Actually, the instructions for my Campy FD clearly say to “fasten the tightening bolt to the frame, torquing to the following values…”
The phrase “to following values” describes a target, not a suggested max. Now maybe other component companies say their Nm number is the max for that part, but until then, it’s more useful to rely on the company that made the part than other sources. Dave, who thinks some torque numbers are conservative because the manufacturer doesn’t know if you’re using more fragile carbon or more robust steel On Fri, Sep 3, 2021 at 11:20 AM Thomas Lawn <thomas.l...@gmail.com> wrote: > This is maybe the biggest downside about torque specs is that it's easy to > lose the natural "hey, I wonder if this is tight enough?" instinct and go > straight to "well it says put it at 9Nm so *crack*!" > > Firstly, the published torque for clamps is not a "target number" to hit, > but actually a maximum. The object being clamped will also have a maximum > value, and for a thin-walled butted seat tube, it may well be less than > 4Nm. For front derailleurs, just tighten until it gets snug and give it > another 1/4-1/2 turn. It should be completely immobile and very easy to > tighten down using the short end of an allen key or p-handle wrench. If you > have to use a long arm to torque a derailleur band, it's likely that > something bad is happening. Don't lubricate the clamp because that will > require more clamping force to resist moving, but you can grease the > threads of the bolt. > > The good news is that there are millions of steel bikes out there with > slight dimples on their seat tube from front derailleur clamps and they're > completely fine. I have a frame with *two* dimples because the Incredible > Hulk installed the derailleur too high or too low the first time. It's also > nearly impossible to detect those dimples unless you're specifically > looking and feeling for them, so you'll likely forget they're even there in > a year or two. > > This may get me some push back (although perhaps not from this crowd) but > I generally do not use a torque wrench on anything involving a metal to > metal interface with a few exceptions (Shimano HT crank pinch bolts being > the most common). With things that are common on Riv bikes like quill stems > and threaded headsets, most of these components were designed before every > mechanic had access to a torque wrench and have no meaningful torque spec > because the limiting factor is rarely the stem and more often the steerer > that fails. These components, and square taper cranks, just need to be > torqued *a lot* but not too much, and finding that by hand is pretty easy > if you go slow, evaluate what you're doing and the effect as you go, and > don't use a wrench that is too big for the job! > > Cheers, > Thomas in Portland, OR > > On Friday, September 3, 2021 at 3:40:46 AM UTC-7 David Hallerman wrote: > >> Dunno about 4Nm being quite a lot. Just earlier this week I installed a >> new, early 21st century Campagnolo front derailleur. And the multi-language >> instruction sheet put 5Nm as the target torque for the clamp. >> >> Dave, who prefers Nm over the other torque metrics because hey Isaac >> Newton >> + + + >> Hudson Valley NY >> >> On Fri, Sep 3, 2021 at 5:26 AM Nick Payne <njh...@gmail.com> wrote: >> >>> That surprises me. I've been fitting band-on front derailleurs for about >>> half a century, and can't recall ever even damaging paintwork, let alone >>> denting a seat tube. Mind you, 4Nm is quite a lot - I'm rather surprised >>> that the marked setting would be that high. I've never used a torque wrench >>> on an FD clamp when assembling a bike, but it doesn't need anything like >>> that much force applied to the pinch bolt to hold the derailleur in place. >>> After all, the handlebar clamp bolts on threadless stems are usually marked >>> as 5Nm; that's sufficient to hold the handlebars in place, and the >>> rotational force on a drop handlebar when you've got your weight out on the >>> brake hoods is many times greater than that on an FD. >>> >>> The other possible problem might be your torque wrench. If it's a torque >>> wrench that goes up to 25Nm or 30Nm, then it's quite likely to have >>> substantial error at low settings. >>> >>> Nick >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "RBW Owners Bunch" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to rbw-owners-bun...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/rbw-owners-bunch/a89596aa-d20a-4f20-a64a-72ec0db5c4dbn%40googlegroups.com >>> <https://groups.google.com/d/msgid/rbw-owners-bunch/a89596aa-d20a-4f20-a64a-72ec0db5c4dbn%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- > You received this message because you are subscribed to the Google Groups > "RBW Owners Bunch" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to rbw-owners-bunch+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/rbw-owners-bunch/76fdb93a-a6c0-4fd3-ab7b-bf52e2b67c8fn%40googlegroups.com > <https://groups.google.com/d/msgid/rbw-owners-bunch/76fdb93a-a6c0-4fd3-ab7b-bf52e2b67c8fn%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/rbw-owners-bunch/CANwgLohhuMVAANoCjzLGctfS4Ex8WSpakJNM-kveX7MDTmDMmQ%40mail.gmail.com.
