Wrench Suggestion

[Lud]

Hrant - I think you are misunderstanding what the margin of error on a torque wrench means in real life. If you use the same wrench on all the lugs on a wheel, they will all be very close. They may ALL be up to 4% off one way or the other, but they will all be off by about the same amount. They will not all be up to 8% (or probably even 4%) different from each other unless your wrench is really hating life.

As for the rest being technical or overkill, if you think so, that's your perogative, but everything I discussed above can easily make a lot more difference than the 4% - 8% you are concerned with here... The fact is many people who are "occasional" DIYers do not know how to properly use a torque wrench, and many times using it incorrectly is as bad, and possibly even WORSE, than not using one at all.

Aaron - I don't personally impact wrench lugs on either, and trust me I know ALL about the stripped studs that can cause! I was just trying to describe the method of tightening it to well below spec and then torquing it the rest of the way. Glad to hear your shop does it the more manual way.

 

[(NSX REY)]

Lud - 5. You can't properly "check" the torque of a bolt with a torque wrench. I know I'm going to piss someone off by saying this, because they and all kinds of "experts" they know have "done it for years," but it's a fact. Try it - tighten a lug to 75 with your wrench, drive around a little, then set the wrench to 80 and torque it again. Most of the time the wrench will hit 80 before the lug will move. A torque wrench is designed to measure as you progressively build to a given torque spec. This means you need to start with a bolt well below the torque setting on the wrench for it to work well, such as Soichiro's suggestion of impact wrenching it to 60 and then hand-torquing to 80.


Lud, you are correct about certain parts not reaching full torque value before the wrench will “Click” and even after you think you have reached torque, try tapping on the bolt you have just torqued and put the wrench to it one one time. You may have to do this many times before actually reaching Torque value. In the case of a wheel lug, driving would simulate the “Torque,Tap,Torque” method. I’ll call it the “Torque, Drive and then torque again” You do this procedure until torque value has been accomplished. You would think that most nuts on any rotating part would need this type of torque sequence, but this is true with non-rotating parts as well. Not claiming to be an “Expert” but I do wrench every day and “Tap-Torque” Is something we must do with certain parts of the engine, our maintenance manuals call out for torquing everything, even a clamp to a wiring harness. So, Lud I have to disagree with you when you say… “You can't properly "check" the torque of a bolt with a torque wrench.” If that were the case why own one? Too low of torque and you could have a part come loose, break and cause fretting between parts, too high of torque and you can cause stress risers in that part… up to failure. Unless you have calibrated hands… a torque wrench is a necessity when wrenching. There are reasons for everything I guess.

 

[(NSX REY)]

HRANT,
Your right this is over kill on troquing “Lug Nuts”… Remember it was en Engineer sitting at a desk that came up with Torque Values applied to given part not the weekend wrench warrior or in you words “Experts with technical talk”. Bottom line is try to get close to the given torque and feel better knowing that you can go mach 1 without your wheels falling off! Geez!

 

[nsxtasy]

5. You can't properly "check" the torque of a bolt with a torque wrench. I know I'm going to piss someone off by saying this, because they and all kinds of "experts" they know have "done it for years," but it's a fact. Try it - tighten a lug to 75 with your wrench, drive around a little, then set the wrench to 80 and torque it again. Most of the time the wrench will hit 80 before the lug will move. A torque wrench is designed to measure as you progressively build to a given torque spec. This means you need to start with a bolt well below the torque setting on the wrench for it to work well, such as Soichiro's suggestion of impact wrenching it to 60 and then hand-torquing to 80.

This is why sjs, in the topic in the Technical DIY forum about axle nuts, noted that you need to back off the axle nut before tightening it to the torque spec.

Originally posted by NSX2B
So, Lud I have to disagree with you when you say… “You can't properly "check" the torque of a bolt with a torque wrench.” If that were the case why own one?

To set the torque, rather than to check the torque value on something that has already been tightened.

 

[Hrant]

Hey Lud, ...... I didn't even realize that my comments can be construed to be directed to you, and even then, why get so defensive ........ and surely when we post here we are posting based on our opinions or perogratives or whatever .......... you make good points ........ but the gist of my comment was to point that we seem to be missing the basic built in error of the instrument (unless TireRack's was superior) ....... and I did use a wink so people get a hint .......!

Hrant - I think you are misunderstanding what the margin of error on a torque wrench means in real life. If you use the same wrench on all the lugs on a wheel, they will all be very close. They may ALL be up to 4% off one way or the other, but they will all be off by about the same amount. They will not all be up to 8% (or probably even 4%) different from each other unless your wrench is really hating life.

.......... let me help you out. I understand your "real life" example but you are missing the point regarding what a reported error means.

An error of +/- 4% means the error can be either off by as much as +4% or -4% at ANY given time. And, This error is a "random error" and not necessarily fixed as you assume. Thus if on one lug nut it errs +4%, it can very easily err -4% on the next lug nut just because that is the "standard deviation" in the calibration; and since this is "random," the difference between the two acn be as high as 8%. For it to err ALL the time at either +4% or -4% consistently is like saying how many times can you get heads tossing a coin. If the error is unidirectional, they could have easily stated the error will be either up to +4% always or down to -4% always on ALL lug nuts. They didn't. So either (a) they are not to savvy to make that distinction, or (b) they deliberately did not say so because it ain't so.

Now, will I still buy a torque wrench that has +/-4% error, yes. Will I pay $89 for one that does the same thing for $19, no. Do I care if one lug nut is 8% off than the other? If my worries are to this level when I am out their driving/tracking the car, then I have must be in the wrong business.

YMMV

 

[Lud]

NSX2B - While you can certainly make sure a wheel isn't going to fall off by "checking" it w/ a torque wrench, you can't accurately determine if it's fully torqued because there is a difference between static and kinetic coefficients of friction.

Hrant - I am not missing the point on what a margin of error is, I'm trying to explain that that it's not being used the way you seem to think it is. You would be right if they really meant it as a true per-measurement deviation error, but it is a margin of calibration error. In other words, it is an <a href="http://traffic.ce.gatech.edu/nchrp2045/v1chapter4_files/image004.jpg">accuracy</a> margin of error, not a <a href="http://traffic.ce.gatech.edu/nchrp2045/v1chapter4_files/image004.jpg">precision</a> margin of error.

As for the difference in price, the $89 wrench will typically outlast the $19 wrench. It also typically comes with a padded hard case, whereas the cheap ones often do not. The cheaper ones probably generally have a greater precision margin of error as well. But for someone who uses them infrequently to torque lug nuts, those things may not be of concern to the buyer. That's why they make both.

Torque is an imperfect measurement to use for this purpose anyway, but it is "good enough" if done properly, and the only practical one to do in your garage. Real tension analysis equipment is completely impractical for this application.

I'm done with this thread. Everyone can do whatever they want. I was just trying to help people who might be interested in doing things the right way.

 

[Taj]

This is kind of off topic but fastener is a very specialized field. There is a group of fastener experts at my work and they can tell you everything about nuts and bolts.

Torque value translates into tension of the bolt (stud in this case). The lug nut and stud basically serves two purposes. The first one is to hold the wheel in place without any displacement so that the wheel is tight against the hub and the second is to prevent the nut from backing out. The specified torque values in the manual are usually set based on a wide range of installation conditions (environmental, temperature, cleanliness….), such as in your home garage, on the track, roadside…etc. If the nut and bolt are dirty with sand on the thread, the torque requires to compensate the friction is a lot higher than a clean lubricated nut and bolt, which translates into a much higher tension value to the bolt/stud with the same applied torque. One of the worst cases is cross thread.

My point is no matter how accurate the torque wrench is, there are other factors that affect the torque value of nut and bolt. In my opinion, the 80 ft/lb is set for preventing the nut to back out.

 

[kgb_agent]

Possible FAQ error

I just found a potential error in the FAQ DIY section.

If this is true...

Ken, using your torque wrench as a breaker can shorten the life of your wrench due to the fact that you are putting a great deal of stress on it as you break loose. I for one own a breaker and never use it, but if I had a $500.00 torque wrench you bet I would not be braking my lugs loose with it. I would take quite a while, but it could break the wrench.

...then the FAQ probably shouldn't reccommend breaking lug nuts loose using a torque wrench. See # 2 in this link:

http://www.nsxprime.com/FAQ/DIY/remove_wheels/removing_the_wheels.htm

Kevin

 

[D'Ecosse]

Ken, using your torque wrench as a breaker can shorten the life of your wrench due to the fact that you are putting a great deal of stress on it as you break loose.

This was mentioned by several people as a no-no, not just AaronR: surely the torque to loosen the lug is the same as that used to tightening spec i.e. 80 ft-lbs either way. I can't see why there is any more stress put on the wrench for loosening vs tightening.

 

[Juice]

Thanks Lud. I'm too lazy to explain to others how to use/treat a torque wrench. All that typing is too much work!

 

[Andrie Hartanto]

This was mentioned by several people as a no-no, not just AaronR: surely the torque to loosen the lug is the same as that used to tightening spec i.e. 80 ft-lbs either way. I can't see why there is any more stress put on the wrench for loosening vs tightening.

I used to use breaker bar to loosen the nut. Now, I just set my torque wrench at the highest setting and make sure the torque wrench don't click when I loosen the nut.

How many of you think you are actually have good enough reaction that you stopped right after it clicks? Most people actually added about 4ft-lbs more than they intended.

Anyway, it is actually better to overtighten the nut than undertightened it. On race cars, we were instructed to tighten it at 90 lb-ft which is 10 ft-lb more than street cars (same car) with same stud size.

 

[jsottile]

What do you guys think about the new Snap On digital Techwrenchs? They have the 1/4'' 3/8'' and 1/2'' electronic torque wrenches.