[Closed] How tight is 50nm?!

Try the hope crank - 70nM they say - my LBS' shop wrench onyl goes to 60

Is just tight enough that about 50nm the other way would be required to undo it. And yes, I do realise that a proper smartypants person who actually knows their stuff about this will refute that by saying it require more to overcome the initial friction or somesuch, but I just wanted to be flippant.

I don't think anything on a bike should be done up so tight that the veins are popping out of your forehead using about nine inches of leverage if that helps.

There are only three real measurements anyway:

1. Veins just about to pop out of forehead.

2. Snug.

3. Soft or delicate thread - needs Loctite.

Pretty much as tight as you can go on the cranks with a standard-sized socket driver i.e. approx. 30cm in length.  The good thing on the GXP BB is that you can not damage the BB bearings through over-tightening.

Just get a metre long extension to your spanner and hang 50kg off the end.

Edit: Hang on a sec, it might be 5kg... let me get a calculator...

τ = r * F

t = torque

r = radius

F = force.(NM being KG * 9.8m/s^2)

5kg on a 1m lever or 1kg on a 5m lever. BOSH

I have managed to over-tighten pedals so much in the past that I have had to use a lump hammer on the tool to shock them undone.

Strangely enough the crankset axle failed in a spectacular spiral fracture a couple of months later........

It's approximately the equivalent of holding 10 pints (in plastic glasses) on the end of a pole 1m long.

I'd probably go for "Hnnnnnnnnnnnt", rather than "GrrrrrrrrrrrrrrrrrrRrrrrrrrrp" It'll be 'reet....

5kg on a 1m lever or 1kg on a 5m lever. BOSH

How much does the lever itself weigh, though?

pretty sure 50 is "hnnnnng" (on a standard ratchet), I may be one or two n's out.

Just get a metre long extension to your spanner and hang 50kg off the end.

Erm. Don't do that. That's 500Nm

5kg on a 1m lever or 1kg on a 5m lever. BOSH

How much does the lever itself weigh, though?

just enoguh to take up the slack between the 49nm that 5kg at 1m would give you due to the acceleration due to gravity being 9.8m/s and not a nice round 10.

Bloody tight! I had to borrow an automotive torque wrench to torque a crank arm power meter to 40 or 50nm. Seems over the top!

50Nm on a crank bolt can be felt on most cranks as a sudden change in resistance as the crank bottoms out on the splines.

5kg 1m

10kg 500mm

12.5kg 400mm

16.6kg 300mm

25kg 200mm

50kg 100mm

yay! new tool time doesn't matter if you can't get to the LBS, 50nm is in the range of normal torque wrenches that can be purchased from any tool shop.

Erm. Don’t do that. That’s 500Nm

Otherwise known as 'FT'.

When I've ask about torque settings on here over the years I tended to get directed here.

https://www.sheldonbrown.com/tork-grip.html

5kg at a metre, so, about 16kg at a foot, call it 20kg on a 9" ratchet handle. Depending how strong you are, well nipped, but not grunty. 💪

HTH.

Edit : what porterjamie said ^

pretty sure 50 is “hnnnnng” (on a standard ratchet), I may be one or two n’s out.

The "hnnnnnng" system of measurement is also my personal choice. If you want to be more exact though as "hnnnnng" can be influenced by the shape and padding of the ratchet handle. You need a combination of the "hnnnnnnng" and the "aaaaaaahhhhh" scale of palm-pain, really.

About half as tight as a "normal" car wheel bolt (normally torqued 90-110NM).

You can get a torque wrench from screwfix for £25, it will be a bit rough but functional enough for that.

Thanks for the responses! lol!

pretty sure 50 is “hnnnnng” (on a standard ratchet), I may be one or two n’s out.

No worries - you have to bear in mind that my responses come from a man who owns a torque wrench but still relies on "hnnnnnnng" as I can either never find it or can't be bothered to use it...........

Can I mention at this point that SRAM's "tighten crank fasteners up to FT torque" design is really crap? If you read the instructions, if you have play after fitting, you tighten it up even more. If you still have play, dismantle, grease and repeat. But it's OK, because you'll get really good at doing it because the GXP BB will probably need replacing before the winter is out. That will give you the opportunity to clear out the crap that has accumulated in the little gap that's left between the crankset and BB too.

Shimano HT2 has a precise bearing preload using the "knurled finger tool" thingy and then a pair of low-torque pinch bolts to hold everything together. And they never, ever come lose when riding (unless you're a muppet and didn't put them together right!)

I'm not saying that everything that Shimano do is good, but a little part of me dies every time I fit a GXP crankset.

yay! new tool time doesn’t matter if you can’t get to the LBS, 50nm is in the range of normal torque wrenches that can be purchased from any tool shop.

Made me smile; when I started maintaining my bike many years ago the general consensus seemed to be that 'proper' mechanics didn't need a torque wrench and relied on feel (being a newbie and cackhanded I was after torque wrench recommendations); I think that carbon components changed things though.

I've always used a torque wrench but you do start to develop a feel over time. A word of advice though (from experience) - use common sense when tightening with a torque wrench and don't keep cranking blindly - it's easy to miss the click or mis-set the wrench!

Question I've always wondered about. Does the value of a given hnnnng vary proportionally to the proximity to exposed chainring teeth?

A word of advice though (from experience) – use common sense when tightening with a torque wrench and don’t keep cranking blindly – it’s easy to miss the click or mis-set the wrench!

Good call and if you're in any doubt at all, start with a lower torque setting and then increase. Don't just blindly follow what it says in the instructions - use your own head too!

have you tried a local garage? their torque wrenches will be in the range you want but their drive will be 1/2" you may need adaptors.

FWIW, I have three torque wrenches in the garage - a little one for doing normal fasteners, a medium one for bigger bike jobs and then a big one for car / caravan wheel nuts. The GXP cranks are, I think, the only thing on any bike that I maintain that needs the big one!

Shimano HT2 has a precise bearing preload using the “knurled finger tool” thingy and then a pair of low-torque pinch bolts to hold everything together.

Except that thy insist on using a 5mm allen bolt which has to be torqued to 13nm, which is more than enough to round out the bolt head once it's been done a few times.

Pretty much as tight as you can go on the cranks with a standard-sized socket driver i.e. approx. 30cm in length. The good thing on the GXP BB is that you can not damage the BB bearings through over-tightening.

Sounds like a plan!!!

"Except that thy insist on using a 5mm allen bolt which has to be torqued to 13nm, which is more than enough to round out the bolt head once it’s been done a few times."

I believe sir is doing it wrong.

I have ht2 cranks dating back to the ark and have had them on and off plenty with this issue happening precisely zero times .

I have had to sort out the aftermath when people have had ago them selves with Xmas cracker Allen keys though

Question I’ve always wondered about. Does the value of a given hnnnng vary proportionally to the proximity to exposed chainring teeth?

No - that's where the aaaaahhhh scale come in.

Can I mention at this point that SRAM’s “tighten crank fasteners up to FT torque” design is really crap? If you read the instructions, if you have play after fitting, you tighten it up even more. If you still have play, dismantle, grease and repeat. But it’s OK, because you’ll get really good at doing it because the GXP BB will probably need replacing before the winter is out. That will give you the opportunity to clear out the crap that has accumulated in the little gap that’s left between the crankset and BB too.

Eliminate the little gap with some washing machine rubber seals that are slightly too small for the axle. They sit at an angle and 'spring/squidge' to fill the gap. It also stops the stupid little insert they had to introduce from wandering out of the BB bearing along the axle and causing massive and immediately noticeable play. Quite why I should have to do this (or SRAM would introduce a wavy washer bodge) for a product costing a reasonable amount of money is beyond me, however. But that is the SRAM way: How many parts does this need? Take that number, double it and add two and that is how many parts it will eventually consist of.

Shimano HT2 has a precise bearing preload using the “knurled finger tool” thingy and then a pair of low-torque pinch bolts to hold everything together. And they never, ever come lose when riding (unless you’re a muppet and didn’t put them together right!)

I had a HT2 crank come off and leave the pedal and crank dangling from my foot on a reasonably high speed descent once. But I'm a muppet. Incidentally, I reckon my buttocks clenched to about 50nM at the time, though.

Except that thy insist on using a 5mm allen bolt which has to be torqued to 13nm, which is more than enough to round out the bolt head once it’s been done a few times.

Only if your allen keys are knackered, I'm afraid. If your worried, swap them for stainless ones - I keep a bag in the garage for just this purpose.

I thought it was measured in knuckles? 50Nm should be about three, possibly four, knuckles when using a standard 1/2" ratchet driver.

On a serious note, I am loving the conversions and now planning on how I can convert these into the various lengths of bar needed to support me for given torque settings, although this may mean either short drivers, or me losing quite a lot of weight.

50Nm is a couple of notches back from pulling out your tripe with a std socket driver.  so tighten it until it goes slack, then back it off a 1/4.

Otherwise known as ‘farm boy tight’

Torque is inversely proportional to proximity and in the direction of various stabby stabby cutty cutty things.

GXP is tight, very.  I'd greased my bearings and did it up tight(ish) so no play, but the BB developed a creak. Re-greased then saw the 50nm. Doh.  Stems are usually 5nm so 50 is very tight - probably as tight as you can go on an 8mm allen key.

Simply tighten until your elbow clicks.

50nm is firm but not too bad with a normal ratchet.

The hub bolts on my car are 200nm AND 180 degrees!  FFS.  200nm is really hard on the torque wrench, then I fit a long pipe to my breaker bar and heave as much as I can, I can only manage about 90 degrees.  I even bought a faffy little angle gague to do it accurately, what a waste of time that turned out to be.

Anyone else twitching at 'nm'? It is quite clear from the context what is meant but it still makes me twitch.  Need help

Sorry.  I meant nM of course.

Was that stricktly neccessarie

Not as tight as I though as I sheared the bolt when refitting my x01 cranks with a normal sized ratchet.

I am quite hamfisted though,

It’s a stupid design, always used Shimano with no torque wrench and never had a issue. I hoped the next generation would see direct mount chainrings with the pinchbolts but the new Xtr have dropped them and gone to one bolt like on the Sram and RaceFace:(

<span style="display: inline !important; float: none; background-color: transparent; color: #222222; font-family: 'Open Sans'; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; line-height: 22.4px; orphans: 2; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;">Anyone else twitching at ‘nm’? It is quite clear from the context what is meant but it still makes me twitch.  Need help</span>

Yes, managed to wait until now to say that 50nm is a distance.

Despite their bad reputation I've been using GXP BB's with SRAM cranks (2 road bikes, and 1 MTB) for ten years with no problems. I put this down to torquing them up to 54nM every time I refit them. I reckon that doing them up too tight helps knacker the bearings.

I gave in last year and got a small bike specific wrench and a normal car type one for not much money.

It's strangely satisfying to feel that click and know that (decent calibration allowing) you are about on spec.

The purchase of a carbon frame and components are really what prompted me to get the torque wrenches. A good investment I reckon.👍

Wikipedia says the symbol for newton metre is N m or N-m.  Dunno what an Nm is.

I've never used NM calibration, as most bike parts have always been at what's speced - a little mechanical appreciation is expected - even 20-30 years ago you could wreck the parts if you were ham fisted - it's the new 'legal sheite' that stuffs manufacturers.

FFS it's always N m with a capital N, as in the name Newton. The man was a genius, please give him the credit he is due.

50Nm on a crank bolt can be felt on most cranks as a sudden change in resistance as the crank bottoms out on the splines.

I'm fond of this approach.  Seen too many stripped threads from click type torque wrenches.  Truth is that after everything is "tight" it is only ever a handful of degrees to stretch the typical fastener.  So feeling for when it goes tight is much more precise than a TW that might never click.  Correct fastener stretch is positional - the thread pitch ensures that.  Trying to back calculate position to a torque, affected by various sources of friction and measured by a mechanism that may be loaded off-axis and may or may not conform to anything approaching a calibration is topsy turvy.

Spring type torque wrenches are more sensible.  Dial spring type torque wrenches are effective as you can see the point where the torque starts to ramp.

Failing that (and preferred), using a proportionally sized lever helps you feel the nipped up point.  Small bolt, small lever.  Big bolt, bigger lever.

apropos of nothing, the correct torque setting for anything made by magura is 0.00005 NM.

Spring type torque wrenches are more sensible.

Ah, now it's pointed out it is obvious. I had always wondered what the point was but now I get it

It's a bit like weather gauges.  I always wondered why people had to tap them to get them to read properly and didn't realise they are actuality designed that way

The world is good.  Well, at least bits of it. Swype keyboards on phones still suck

Not tight enough if you don’t use locktite 243 on the collar nuts holding your rear sprocket onto the carrier of your rear wheel on your KTM950SM☹️  Cheapskate garage that previous owner used......

At work we have a special unit of Torque named after my old boss who worked on Harriers.  These used to shake a lot and everything was done up FT and loctited apparently.

He carried this over onto his new industry where he’d often be heard going “little bit more, little bit more, fu@k it!”.

So we named that amount in torque where you just begin to feel the threads collapse on any size bolt/screw/nut as “1 Spellman”.

Just remember that next time you strip something😁

These used to shake a lot and everything was done up FT and loctited apparently.

FT is an ISO standard measure of torque these days...

apropos of nothing, the correct torque setting for anything made by magura is 0.00005 NM.

Does big M mean "Mile"?

Still a low torque value FWIW.

[SI unit pedant]

Confusing thread title!  50 nanometres is indeed a tight gap - but while 50 Nm is high for compared to most bike parts, it's not really that tight; my car wheel nuts need 120 Nm.

[/SI unit pedant]

Otherwise known as ‘farm boy tight’

I'm pretty sure this is what it says in the GXP specs (or it should do).

I carry an extra big tool when riding the bike with carbon SRAM cranks. No weight saved.

No worries – you have to bear in mind that my responses come from a man who owns a torque wrench but still relies on “hnnnnnnng” as I can either never find it or can’t be bothered to use it………..

Same as me, bought a torque wrench for when i had to do a head gasket on my old Escort RS Turbo back in 2004

Has been sat on the shelf ever since......

Never use a torque wrench on a bike, all done by feel, even with 10k carbon road bikes

Know of pro road bike mechanics who wont/don't use them too

Bit like Italian wheel builders who refuse to use a tension meter, they would rather "pluck" the spokes and listen to the frequency of each spoke to get the same tension

Wikipedia says the symbol for newton metre is N m or N-m.  Dunno what an Nm is.

Sounds like rubbish to me. In science units are always placed next to each other like kWh or with a -1 superscript to denote 'per' like ms-1.

Never use a torque wrench on a bike, all done by feel

How do you know what it's meant to feel like? I don't think you do, you just think you do. I often don't use one now but that's because I own one and have used it in the past, so I do know what it's meant to feel like.

Stem bolts and disc bolts need far less torque than you think.

1nm tighter than 49nm 👍🏼

When the force results in 'just beyond a fart' but also 'just under a poo'.

I’d like to see someone apply 1 nm. Hint 1 nM is of course nano mole  or 6.023 x10^14 molecules. Newton’s are always in capitals. Units matter.

How do you know what it’s meant to feel like? I don’t think you do, you just think you do. I often don’t use one now but that’s because I own one and have used it in the past, so I do know what it’s meant to feel like.

Stem bolts and disc bolts need far less torque than you think.

Well after 30 years of building cars and bikes including bikes for pro athletes Ive learnt to know when something is about to give or when something has enough pressure and needs no more

Ive only had one or 2 bikes come back with an issue out of the 1000's Ive built

"I’d like to see someone apply 1 nm. Hint 1 nM is of course nano mole  or 6.023 x10^14 molecules. Newton’s are always in capitals. Units matter"

Context is importanter.

"Never use a torque wrench on a bike, all done by feel, even with 10k carbon road bikes

Know of pro road bike mechanics who wont/don’t use them too

Bit like Italian wheel builders who refuse to use a tension meter, they would rather “pluck” the spokes and listen to the frequency of each spoke to get the same tension"

Those two things are nothing alike.

One is guessing the other is a measure.

Most all bike fasteners will be tightened into the elastic clamping zone, to some degree. This should be detectable as a sharp uptick in the perceived resistance as the joint moves beyond frictional and alignment/seating torque. An experienced mechanic will likely be able to judge the feeling of this transition and perhaps will then apply the correct degree of rotation beyond that point, corresponding to an appropriate degree clamping load on the joint...or not.

www.pcb.com/Contentstore/mktgcontent/WhitePapers/WPL_23_Understand_Torque-Angle.pdf

Worth a look to understand the feel of doing up a bolt.

Point of interest, approx 70-90% of bolt rotation resistance is frictional, so don't grease threads and apply a torque measurement for non greased joints, dropping friction by, say 50% could cause you to hugely overtension the bolt.

But that is the SRAM way

I thought the SRAM way also involved coming out with interesting ideas then not developing them any further (See: Hammerschmidt and Automatix hub)

Well after 30 years of building cars and bikes including bikes for pro athletes Ive learnt to know when something is about to give or when something has enough pressure and needs no more

But you don't do bolts up until they are 'about to give' - that's usually too tight.

The torque for a bolt depends on all sorts of things, including what it's clamping.  I used to do the same as you, then I got a torque wrench and I realised that sometimes I was okay, and others I was too tight.  For example, as I had endless trouble with my Marzocchi forks I ended up taking them apart a lot.  I did the legs up to what seemed reasonable and not too tight, but after twenty or so goes the bolt/valve stem snapped.  Under-specced, perhaps, but the official torque specs really aren't very tight and I'd been overdoing it.

Of course at this point you'll assume I'm a ham-fisted idiot who has no clue mechanically (I'm not)...  so I don't even know why I'm posting this 🙂  Fortunately for you and everyone else who doesn't use a torque wrench, the margin of error is usually pretty big.  Before I got a wrench I never had issues either except maybe a couple of disc brake bolts when I first got disc brakes.  The torque on those is really low btw.

I’d like to see someone apply 1 nm. Hint 1 nM is of course nano mole or 6.023 x10^14 molecules. Newton’s are always in capitals. Units matter.

A bit of a non-sequitur there, how does explaining what an nM is help judge what an nm is?

Also the abbreviation for a mole is mol, presumably because the metre had already bagged m.