Guestimating Torque
 

I have a $120 Huffy cruiser bike arriving in a box from Walmart tomorrow. And note that that price point is because it's the deluxe model with rack, basket, and drink holder. Seat to put a Laz-E-Boy to shame.

To my horror the "easy to assemble" consumer-level instructions include needing a torque wrench, and give torque specifications for various parts. (Passive-aggressively not mentioning that this obscure and expert tool could cost more than their cheap bikes.)

I've decided that I'm neither spending $40 for the wrench, nor $75 having a local bike shop assemble the bike for me.

I'm wondering if it is conceivable for me to get a focused answer to the following question... without having the thread disintegrate into everyone's unkind opinions of Huffy bikes, Walmart, and the mortal sin of not having an LBS put your bike together:

After hand-tightening the bolts that hold the front wheel on, about how many more rotatations (or part thereof) should I turn the bolt with a wrench, to approximate 17-26nm (12-18 foot pound) of torque?

Thanks

Rotations won't really apply here. Lubricate the threads with grease or oil and apply ~20-25 pounds of force on an average-length box-end wrench.

I've heard Harbor Freight Tools has some pretty affordable torque wrenches if you do want one... lessee here... http://www.harborfreight.com/3-8-eig...rench-807.html 20 bucks.

Most of the fasteners on you bike will be ok with just being tight(T), the wheel nuts you may want to get real tight(RT). The seat post binder could be made real f****** tight(RFT) if it slips. There is nothing that is required to be super f****** tight(SFT).

BTW you could rent a torque wrench from an auto-parts store, too, I believe. A bit of a hassle, I'm sure... before making a trip there and back, I'd just spend the $20 instead.

Those torque specs in the "easy to assemble" consumer-level instructions are just there for the lawyers; experienced feel works fine for torquing fasteners on anything bike-related that isn't carbon or low spoke count.

When you look at at a fastener, try to imagine how much force it'd take to strip the threads, and don't use more than half of that, or maybe 75% in a pinch. The only fasteners that need to be really tight are rear wheel nuts/skewers on bikes with horizontal dropouts, and perhaps the bar clamp bolt on single-bolt stems. Then a whole bunch of other things need to be pretty tight, like pedals, all locknuts except the ones on barrel adjusters, seatpost, stem and brake cable clamp bolts, and I think most everything else just needs to be tight.

Just try to imagine how much the threads can take as you're tightening, while also considering how tight it needs to be. I'm not sure to what extent consideration can be a substitute for experience, but I do know that it can. Just keep your brain in gear.

Imagine a foot long wrench with a 12 to 18 pound weight hanging off the end of it. That's 12 to 18 foot pounds.

I agree we worked on bikes for years and never used torque wrenches. While i was going through basic Aviation mechanics in the Marines I was taught that most all tools are sized to approximately the correct amount of torque to the fastener they are tightening.

I believe the recent increase in tourque related notices has more to do with liability than with mechanical performance.

smaller the allen wrench the shorter it is , as well ,
don't hold the little ones at the end,
and it's harder to over leverage them

I highly recommend refusing to accept the shipment.

Torque wrenches are cheap and have lots of practical uses. I'm not sure what is "obscure" or "expert" about them that would inspire "horror."

If you had instead bought a bookshelf kit, would you sulk if they forgot to throw in the allen wrench?

yeah there's no way a wal-mart bike needs an actual torque wrench to assemble if you have basic mechanical intuition and experience.
the biggest place where torque wrenches are actually important for mechanics to use, is tightening clamps around carbon fiber seatposts or handlebars, and some cranksets.

And cf steerer tubes.

Exactly. Not to be unkind but I think the OP could assemble his Huffy with a hammer and a pipe wrench and not cause any damage. Ultra light and thinwall are not in this bike's lexicon.

No, I honestly don't think so.

Even the walmart bikes assembed in-store dont get torqued to specification; their employees aren't allocated propor tools.

That said, areas I commonly see fail on walmart bikes from lack of torque:
pedals -unscrews itself
crank arms -securing bolt drops out, crank works loose
stems -handlebars rotate independantly from fork under high force
be sure to secure these areas 'really darn tight' and use grease

after that, concern yourself with getting the brakes adjusted right; you will probably need to true the wheels first to make this possible
then you'll need to adjust the derailers....
etc
plenty of tutorials on various adjustments online

:roflmao2:

I am wanting a torque wrench with just those settings. :thumb:

Someone who does a lot of mechanic work will have a feel for nuts and bolts and be able to get by without a torque wrench. Based on your post, you don't seem to be that person.

Lift something that weighs 10 lb - e.g. a gallon of water weighs about 8.3 lb plus container. Then imagine exerting that force at the end of a 1 foot wrench handle, that is 10 ft-lb. For a six inch handle, 20 lb would be the same torque (1/2X the length needs 2X the force).

Or, for a typical adult male who isn't unusually strong or weak, if the threaded part of the bolt is the diameter of a standard cigarette or pencil, hold the wrench handle so close to the bolt or nut that your thumb can wrap around the bolt or nut. If you tighten using your wrist strength only - so that your elbow doesn't move at all, no shoulder or whole-body involved - you'll be hard-pressed to over-tighten the bolt. If the thread is the diameter of a Sharpie, move your hand further out the handle until your thumb can just barely touch the bolt or nut, and then same idea with the wrist strength. If the thread is smaller than a cigarette, hold the wrench close to the bolt or nut (usually the handle will be short anyway) so that your thumb is on the bolt or nut and just two fingertips are pressing on the wrench handle, then tighten with only wrist and those two fingers.

If either the bolt or nut or whatever is being screwed into is aluminum, then be particularly wary of stripping the threads. The wheel nuts and axle on your Walmart bike are steel, and pretty large diameter, so will be hard to strip those threads.

If you are really concerned, spend $4 for some threadlocking compound (autoparts store, hardware store) and use that when assembling the bike.

Choke up on your wrenches to a point that you physically can't over tighten.

"Torque it till it strips, then back off half a turn"

It's just a walmart bike. You can't hurt it that badly, and even if you do, it doesn't matter that much. More than likely all the other bolts and nuts on the bike are at the wrong torque, the bearings aren't greased or preloaded properly and the spokes are too loose. For the cost of having it assembled right, you might as well buy another bike.

As noted, see #14 above..............:love:

Yeah Fedex tracking says the box weighs 53 lbs (?!). Not the Huffy carbon fiber model. Real Steel. Should be pretty robust. I guess the good point is that after I get the thing moving, inertia will carry me for the rest of the ride. And if anybody "doors" me in the bike lane... I'll take that Mercedes door with me.

Thanks to (almost) all of you for useful answers. I much prefer the "pretty tight to really damn tight" scale to both Newton Meters and Pound Feet.

I'm actually going to try to balance a 20 lb weight on the horizontal wrench handle to see if it turns any more. Would this qualify as a "Mythbusters" experiment?

Regarding brakes and derailleurs it's fortunately a one-speed, pedal-backwards-to-brake deal. I actually wouldn't try to assemble a more complex bike myself. I'm going to visually inspect the wheels for truthiness and... just return it to Walmart if they're warped and wobbling. I am good enough with a wrench to probably not strip bolt threads. Loctite is sounding tempting for my more likely undertightening.

Regarding Harbor Freight Tools the customer reviews on their cheap "clicker" torque wrenches are scathing -- one from a guy saying he went through all the wrenches in stock at a store and none of them were working right. And in general I'm reading that "clicker" types need professional calibration (even after having been shipped) to be at all accurate. Not sure of the economics of that for a $20 wrench.

I'd go for the more reliable if less exact "beam/needle" type. There are very cheap ones to be found ($10) but only in 0-150 foot pound (½-inch). BUT, Sears has a new 3/8-inch 0-75 foot pound model (should be just OK for 6-35 pound foot range I guess?) coming out next month for $17.99 with free ship-to-store for anyone interested:

http://www.sears.com/shc/s/p_10153_1...9&blockType=G9


Well I'm out of here now. And on this bike not certain to live to post again. I know how hard it was for all of you to not "h8 on my Huffy", and appreciate your effort.

This is way too much thought for a crappy walmart bicycle. Tighten the bolts tight and then spin the wheel and notice it's out of true and then ride it.

I have a 15 pound carbon/titanium and I assembled the whole thing without a torque wrench and didn't think twice about it. If I'm assembling an engine or tightening certain suspension bolts in a car I'll pull out one of the torque wrenches.. but actually most precision tightening doesn't call for torque measurements anymore since the lubricant/lack of lubricant in the threads can affect the actual tightening vs the torque applied.

I have always thought that the difference between an experienced good mechanic and an average one is the ability to sense and feel torque/bearing play/etc. I see a lot of bike mechanics who really have a hard time knowing just how loose or tight a bearing is unless they ask someone. I also see a lot of bike/car mechanics who just don't get "it" when they are tightening down a fastener that they need to slow down or stop. They don't understand the difference in feel between a nearly fully tight fastener and a still too loose fastener. Same with tightening nipples on a wheel. I have noticed that I can feel the differing tension building in just how the nipple feels as i tighten it. A lot of people who are newbies at building wheels (like me!!) fall into two camps, the people that understand how torque/tension feels and the ones that don't and have to purely rely on tools like tension meters to judge their wheel builds.

The feel of torque and tension is a very learned behavior.

+1.

You have to strip a few fasteners until you get the feel of how tight is tight for a given bolt diameter and material.