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Why Buy A Torque Wrench?

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Why Buy A Torque Wrench?

Old 04-12-16, 08:22 AM
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jyl
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Why Buy A Torque Wrench?

I see considerable discussion here about which torque wrench to get.

My question for you all is, why get a torque wrench at all?

I have never used a torque wrench on a bicycle, and haven't ever encountered a need for one.

(Yes, I do know about torque wrenches and own two. I use them for car work.)
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Old 04-12-16, 08:26 AM
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Originally Posted by jyl View Post
I see considerable discussion here about which torque wrench to get.

My question for you all is, why get a torque wrench at all?

I have never used a torque wrench on a bicycle, and haven't ever encountered a need for one.

(Yes, I do know about torque wrenches and own two. I use them for car work.)
If you have carbon bikes, it can save you from cracked tubes if you don't know what you're doing. Equally almost every bolt on a bike will have a specified torque to tighten to, so it takes a lot of the guesswork out of things to just set your torque wrench to the value and tighten to it.

But yes, for most home mechanics it's not an essential tool.
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Old 04-12-16, 09:26 AM
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I didn't get one until I had to deal with some carbon stuff. I really only use it for that.
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Old 04-12-16, 09:47 AM
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You bikes and your responsibility, sure, do without one for everything. If you are working on other people's bikes, it's better to have an objective measurement. I do know that studies have shown that even experienced mechanics have a very poor record at estimating the torque they apply.
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Old 04-12-16, 10:45 AM
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I have two. A small one for high end stems and the like as has already been mentioned. I was surprised to find how low the torque spec is for some of those parts. If left to my own judgement, I would definitely over cook them.

I also have a big one that I use for bottom brackets and crank arms. The torque spec for many of those parts is 30 ft/lbs. That's a bit more than I would probably use if left to my own judgement. If you read the bike mechanics posts for any length of time, you will see lots of posts regarding left crank arms coming loose from square taper cranksets. That's the result of under torqueing those parts. There are a lot of those posts so I'm assuming under torqueing is common.
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Old 04-12-16, 11:06 AM
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Originally Posted by Retro Grouch View Post
I also have a big one that I use for bottom brackets and crank arms. The torque spec for many of those parts is 30 ft/lbs. That's a bit more than I would probably use if left to my own judgement.
I agree. Even for bottom brackets I often leave it to my own judgment. This weekend I installed an Italian threaded bottom bracket. I figured that was a good case for making sure I used enough torque. Sure enough, I had to take the bike out of the workstand to get enough leverage to meet the torque spec.

For carbon bits, I've got one of the little fixed torque keys. Besides keeping me from breaking things, those are super easy to use.
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Old 04-12-16, 11:38 AM
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I imagine they are useful for acquiring skill, i.e. knowing how hard to turn each type of bolt. But it's too late for you and me.
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Old 04-12-16, 12:53 PM
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If you're an anal-retentive, OCD type like I am, it takes all the guess work and worrying out of the job.

If you're like a friend of mine who always says: "a quarter-turn tighter" then "ping" the snapped bolt flies across the room, it saves time and hardware.

I always use a torque wrench. The only part on a bike I stopped using one is to secure Campy Ergo levers to the bars. I think their recommended spec. is too high. I've cracked two bodies before I decided to tighten them by "feel".
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Old 04-12-16, 01:06 PM
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I always use one, too. I figure that since effort is such a subjective feeling, I might as well use one to eliminate guesswork. I've never had a crank fall off in 7 years and 20,000 miles of working on my own bikes, so I must be doing something right.

Like others, I already had my torque wrench from car work, so I didn't need to buy one for bike stuff.
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Old 04-12-16, 01:56 PM
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According to his profile, all of OP's bikes are of a time when steel was not just real but likely the only option. He may not need a torque wrench but those with carbon things will.
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Old 04-12-16, 05:53 PM
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A Torque wrench makes 'How tight?' translated into a standardized Number .. you can print in a Repair book or on the Part.
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Old 04-12-16, 05:55 PM
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My opinion would be once you acquire an experienced feel torque wrenches are only necessary for critical bits. And understanding what those are and one's "feel" limitations comes with....experience. If you're unsure get and use a good torque wrench.
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Old 04-12-16, 07:34 PM
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My automotive torque wrenches can't measure down to 6 Nm!
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Old 04-13-16, 02:29 AM
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Originally Posted by jyl View Post
I see considerable discussion here about which torque wrench to get.

My question for you all is, why get a torque wrench at all?
Because, in a slight mis-quote "common sense isn't common at all".

Although here, replace "sense" with "experience" or "good judgement".

And the base engineering margins present in any given design are no more standardised than the functional requirements for a certain user and usage profile is.

Some combinations of parts, users and usage profiles have a HUGE span of acceptable performance.

Spoke tension for a low-mileage SS or IGH for instance.

Others, not so much.

Just like with a tensiometer, a torque wrench makes it easier to get it right, and if stuff fails, you're far better set to figure out what went wrong.

Had a friend who trashed several stems by overtorque before bringing in some help.
When he finally asked I quickly discovered his headset was missing a centering piece, which caused the headset to quickly lose adjustment - which he'd tried to cure through the application of more torque.

He'd probably researched things more closely sooner, if he'd known that HIS part was done right, and the thing still didn't work as expected.
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Old 04-13-16, 06:08 AM
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I've been using torque wrenches all my life on cars etc, & in industry like all tools they have evolved over the years into so many different shapes & sizes, the one I now use on my CF bike is a very small little palm hand held one, OK its preset at 5.nm, these were unheard off a few years ago.
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Old 04-13-16, 06:48 AM
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Originally Posted by dabac View Post
Some combinations of parts, users and usage profiles have a HUGE span of acceptable performance.
That exactly why so many bike mechanics got by without using a torque wrench for anything for so long. Steel frames, bottom bracket cups and steerers, rugged aluminum parts, etc. were very tolerant of "close enough is good enough" toque settings. The advent of more fragile carbon stems, steerers, handlebars, seatposts, etc. made objective torque measurements far more necessary.

I use a torque wrench for bottom bracket cups, crank arm bolts (both square taper and HTII pinch bolts) and tightening stems clamp bolts onto carbon steerers but almost everything else is by "feel".
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Old 04-13-16, 07:03 AM
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Originally Posted by dabac View Post
Although here, replace "sense" with "experience" or "good judgement".
"Good judgement comes from experience. Experience results from bad judgement." Mark Twain, one of my favorite Missourians.
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Old 04-13-16, 08:55 AM
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Be wary of the "great" mechanic that tells you he can do everything by feel.

In my job as a tech specialist for the company, I took uncounted call backs on techs that thot they could adjust things by "feel"!!!!!
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Old 04-13-16, 12:26 PM
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Originally Posted by rydabent View Post
Be wary of the "great" mechanic that tells you he can do everything by feel.

In my job as a tech specialist for the company, I took uncounted call backs on techs that thot they could adjust things by "feel"!!!!!
If you are a mischievious type, with a couple of mechanically inclined friends, here's something you might enjoy:
Get a sheet of plywood etc, stand it upright. Drill a hole at about waist level. Put an extender on a click-type torque wrench, put extender through the hole and secure the wrench with some brackets. Hand out an adjustable wrench, and have people guess the torque setting from the "blind" side of the plywood sheet.
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Old 04-13-16, 12:52 PM
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I am trying to think if I have ever stripped a fastener on a bike due to excess torque. I'm pretty sure the answer is no, never.

I am also trying to think if I have ever had a fastener come loose on a bike due to insufficient torque. I can only think of a couple of rack and fender bolts. And one quill bolt that I forgot to torque at all. I'm not counting 25.4 mm bars in 26 mm stems and weird mismatched stuff, or Wald baskets clamped to handlebars with crummy sheet metal straps.

Perhaps if I was working on CF bikes, I'd use a torque wrench. Or if I was working on other people's bikes for pay, and wanted an extra line of defense if my work was later questioned. But it would be just as easy to add a drop of blue LocTite.

Torque is not hard. 6 ftlb means applying 6 lb force at 1 foot from the fastener, or 12 lb at 6 inches. Lift a full milk jug, that is 8.5 lb. That amount of force will get you close enough.

For cars, the forces are much higher so a torque wrench makes more sense. Lug nuts at 55 ftlb, etc. I recall one suspension bolt that was spec'd at 250 ftlb. Ugh.
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Old 04-13-16, 01:08 PM
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Originally Posted by jyl View Post
I am also trying to think if I have ever had a fastener come loose on a bike due to insufficient torque. I can only think of a couple of rack and fender bolts.
The reason is more that the difference in a tight enough bolt and a split piece of carbon, or crimped thin wall alloy tube, can be an imperceptible amount of turning. Ultralight parts must be affixed precisely, or they will likely be damaged.
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Old 04-13-16, 01:20 PM
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Originally Posted by jyl View Post
I am also trying to think if I have ever had a fastener come loose on a bike due to insufficient torque.
6,400 posts and you're on the "Bicycle Mechanics" board. So how many "Left crank arm fell off" threads have you read? Your original question was "Why get a torque wrench at all?" There's your answer.
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Old 04-13-16, 02:03 PM
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Originally Posted by jyl View Post
I am trying to think if I have ever stripped a fastener on a bike due to excess torque. I'm pretty sure the answer is no, never.

I am also trying to think if I have ever had a fastener come loose on a bike due to insufficient torque. I can only think of a couple of rack and fender bolts. And one quill bolt that I forgot to torque at all. I'm not counting 25.4 mm bars in 26 mm stems and weird mismatched stuff, or Wald baskets clamped to handlebars with crummy sheet metal straps.

Perhaps if I was working on CF bikes, I'd use a torque wrench. Or if I was working on other people's bikes for pay, and wanted an extra line of defense if my work was later questioned. But it would be just as easy to add a drop of blue LocTite.

Torque is not hard. 6 ftlb means applying 6 lb force at 1 foot from the fastener, or 12 lb at 6 inches. Lift a full milk jug, that is 8.5 lb. That amount of force will get you close enough.

For cars, the forces are much higher so a torque wrench makes more sense. Lug nuts at 55 ftlb, etc. I recall one suspension bolt that was spec'd at 250 ftlb. Ugh.
So is your question "Why should I use a torque wrench for bike work?" or "Why would anyone use a torque wrench for bike work?"

A lot of us have been answering the latter question, but you seem to actually mean the former. If you haven't needed to use one thus far, then don't. Congrats. It's simple.
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There's no such thing as too far.. just lack of time
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Old 04-13-16, 02:39 PM
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Many, perhaps most, people coming to this board are not working on high end carbon fiber components.

From the threads I read, I think most are working on bikes and repairs that, in my opinion, do not require a torque wrench. Steel fasteners into steel threads or large diameter aluminum threads.

Which makes a $100 torque wrench an unnecessary expenditure for most people here. A fun thing to have, sure, but not required or even all that useful. If money is at all tight, skip the TW.

That is something I think should be made clear to the beginning DIY bike mechanic who comes here wondering what tools to buy to work on his commuter bike. And hence I started this thread.
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Old 04-13-16, 02:42 PM
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I would like to NOT damage the carbon tubes on my bike. If 5 nm is what my seatpost clamp calls for, it's getting 5 nm of torque. If you don't have any carbon or thin walled alloy, you likely won't need one. It's not really a hard concept to follow.
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