5 sheared studs and the wheel falls off...

[robinlsb]

I would peg this as a major possibility. MOST shops use torque-sticks when doing lug nuts with impact guns. It's usually the newbie who hasn't actually taken any auto-tech classes that makes the mistake. Impact guns can do up to 650 ft-lbs now-a-days. An uncalibrated finger can "butta-butta" a lug nut to over 100ft-lbs without even knowing it.

 

 

 

Using a 250 ft-lb torque wrench on a 70 ft-lb bolt is less than ideal. You want your expected torque values to fall close to center on the wrench range. I'd check your wrench. It might only be calibrated from 100 to 250 ft-lbs.

 

10 ft-lbs might be enough. I haven't done bolt-stretch calculations in a while. It only takes one time exceeding the yield strength of a bolt to ruin it. Period. One dumb newbie zapping a lug to 100ft-lbs spells failure. Once you yield the bolt, all stability is lost.

 

Strength and materials 101:mad:

[BAC5.2]

+1. The hub DOES take some of the forces appiled to the wheel. To say it does not is inaccurate IMO but I ain't in the arguing mood today.

 

Not really. I haven't tried (though I might), but I bet you could slide a feeler pick between the hub protrusion and the hub bore in the wheel. If there is no contact between the hub protrusion and hub bore, no load is carried. In fact, the load carried is proportional to the contact pressure. Any contribution by the hub protrusion is FAR eclipsed by the loads carried by the lug studs, at least an order of magnitude.

 

Heck, some hubcentric rings (like the ones that come on some Rotas) are plastic. I ran a set of them for a long while at 400awhp (actually, only two of the wheels had the rings. The other two did not).

[BAC5.2]

Strength and materials 101:mad:

 

Why the mad face?

[BAC5.2]

That could be the answer!!!!!!!!!! Once over torqued, you can't go back. I am sure that the remove torque would not be noticed by you. Yet, if the studs were over torqued, they could have been weakened, setting up the ultimate failure.

 

That would explain the catastrophic failure of all the lugs, more or less at the same time. It would also tell you to replace the front lugs on the other side to be safe.

 

My guess is the dolt who replaced the front wheel bearings used an air wrench set for steel wheels.

 

However, since the bolt ends are so dinged up, I would stick with vandalism, unless the insurance company has an electron microscope.(

 

The right rear fell off. I don't think the front wheel bearings have anything to do with it.

[SubLo]

Not really. I haven't tried (though I might), but I bet you could slide a feeler pick between the hub protrusion and the hub bore in the wheel. If there is no contact between the hub protrusion and hub bore, no load is carried. In fact, the load carried is proportional to the contact pressure. Any contribution by the hub protrusion is FAR eclipsed by the loads carried by the lug studs, at least an order of magnitude.

 

Heck, some hubcentric rings (like the ones that come on some Rotas) are plastic. I ran a set of them for a long while at 400awhp (actually, only two of the wheels had the rings. The other two did not).

 

Umm... no. Not sure about our Leggies but on many cars, the clearance on the hubs to hub bores is nearly nothing a couple of thousandths - like on my truck. I assure you this is the case as I've measured it with a micrometer and have had custom hub rings ordered and it does indeed carry the majority of the load. Plastic hub rings DO carry substantial load. They are not soft plastic but are designed as such (mine are aluminum). Properly designed, they are stressed all around in a fashion where the whole structure is supported. Think pressuring an egg equally from all points. My truck lugs pretty much just hold the wheel in place.

 

BTW, not to bring this argument up again but I can't keep my mouth shut. Conical lugs center the wheel but not very well. In an application designed for hub-centric wheels, where the hub is designed to center the wheel/tire, and you go aftermarket rims and non-hub-centric, it's really tough to get as nearly centered and a good balance not to mention again the load shifting argument.

 

And yes, even a high-strength lug can easily be sheared or strained to failure (in reality, a shear force anyway - just in different directions) by a couple of bad applications of an impact gun. I've done it.

[BAC5.2]

You can look at the hub protrusion in the picture of the broken stud. The fact that rust has built up on the protrusion is proof that there is minimal contact. No contact = no load carrying capacity. Load carried is proportional to the stress between the hub and it's mating surface. Standard interference fit mechanics.

 

If there are thousandths of an inch between the hub and the bore, that is too much.

 

Rotating shafts are a good example to visualize things. A few thousandths of an inch clearance between a rotating shaft and a gear means no torque transferred through the shaft to the gear. To get any significant torque carrying capacity, you have to press-fit the hub onto the shaft.

 

We are talking about THOUSANDS of pounds of preload on the lugs. At 70ft-lbs, there is almost 8500lbs of preload PER LUG (assuming a grade 8-bolt, and a reasonable approximation for area). I could calculate the actual values if I cared enough to take measurements. At 80 ft-lbs, with the same dimensions, you are looking at 9700lbs of preload. And that is PER STUD.

 

Any contribution by the hub interference is minimal in comparison. Especially since there isn't actually any interference. The best argument you could make is that the hub protrusion helps to align the wheel better than the lug studs and conical lug nuts do. I disagree that the lugs don't center the wheel well. You have 5 points of reference to align the wheel with rigid reference points (the lug studs themselves). The lugs WILL center the wheel around the 5 points of reference. The hub protrusion simply helps line things up prior to torquing down the lug nuts.

 

Again, the presence of rust on the hub is proof that there was never contact. Oxide layers are thousandths thick. The hub protrusion, on a Subaru, does nothing to support the load of the car.

[LittleBlueGT]

I totally agree with the once majorly over tightened theory, thus stretching all of the lugs, setting up for the climactic mass stud failure.

[hadvw]

So.. Am I asking for trouble by tightening lugs by hand without a torque wrench?

 

I'm the guy who loosened/tightened our wheels for summer/winter tires in Ontario when helping my dad by standing on the lug wrench. We did this plenty of times, and never had any issues ('82 Civic Wagon with steels, '79 Dodge with steels, '87 Jetta with alloys/steels, '89 VW Fox with alloys/steels plus my cars: '84 Jetta with alloys/steels, '90 GTI with alloys, '94 Corrado with alloys).

 

I can't be the only one who does this.

 

For our '05 LGT, I've only taken the wheels off myself once or twice, and I usually just go with "about as tight as before" (and have not stood on the wrench). What kind of lb-ft value are we talking about for catastrophic failure? 90 lb-ft vs. 70? I'd imagine that since wheels/tires are still one of the major DIY items out there for people switching to snow tires, there'd be a massive safety margin - like 120 or 150 lb-ft before you really over-torqued a bolt..

[LittleBlueGT]

I have taken my wheels off likely 100 times, maybe more, and I am not alone, countless others with summer/winter/track, numerous suspension mods have done the same.

 

I think this case is unique in someone likely giving them a good 250-300 ft/lbs once.

 

If you go by hand and get 150 ft/lbs vs 85 or so, I don't think that will cause any damage.

[BAC5.2]

It's not expensive to get a 3/8" impact gun that'll spit out 450 ft-lbs or more. Ingersol Rand makes a 1000 ft-lb 1/2" gun that's relatively cheap, and their 650ft-lb model is industry standard for good quality for a good price. It IS likely that a shop installing the wheels had a newbie use his brand new IR-650 set on full blast to do one or more of the wheels. Any more than 5 impacts at wide open throttle is going to be well over 200 ft-lbs.

[FPerron]

It's either sabotage or someone's not telling the truth.

[robinlsb]

It's either sabotage or someone's not telling the truth.

 

I'd vote for option B.

[BAC5.2]

Any update?

[rob]

Basically the insurance company filed it under comprehensive with the estimation that the lug nuts were too loose or over torqued. They didn't spend any time trying to figure it out. In the end, I had no out of pocket expenses and as comp, it the claim doesn't count against me. It was my first claim experience with MetLife and it was perfect. The car came back better than before the incident, so it all worked out. Well except for the part where my family almost died on the freeway...

 

The final bill on the damage was right around $4k. That included a new rear fender, bumper, wheel, suspension parts, etc. After all this time I JUST picked it up last week. It took them three tries to get the paint right. Apparently the paint mix details for Garnet Red Pearl that Subaru provided to the paint manf was wrong. They had to adjust the formula and issue an update.

 

As for the reason for the wheel breaking off, no one had a better guess than what has been suggested here. Everyone I talked to pretty much said it was either unheard of or pretty rare. I am going on the assumption that the lug nuts had been severely over torqued at one point and one or two studs failed. When I got the car back I replaced the remaining wheel studs for piece of mind.

 

The whole thing just creeps me out. Now I am paranoid of my other cars and will likely do stud replacements on those as well.

 

-Rob

[rob]

Originally Posted by FPerron http://legacygt.com/forums/skynetim/buttons/viewpost.gif

It's either sabotage or someone's not telling the truth.

I'd vote for option B.

 

And what exactly are you implying?

[GTTuner]

Originally Posted by FPerron http://legacygt.com/forums/skynetim/buttons/viewpost.gif

It's either sabotage or someone's not telling the truth.

 

And what exactly are you implying?

 

I think he meant someone had the wheel off and did not torque it properly. :confused:

[Frogg]

This has happened to me twice...but both times running spacers and not enough contact....The second time the wheel bounced over the car behind me...could have killed them if it went through the windshield....

[broknindarkagain]

When was the last time the car was in the shop with the tires off?

 

Leaving lugs lose will not sheer them off like what happened to you. If they are over torqued however, this can and most likely will happen. Any shop you ever go to will use an impact wrench to remove and install lug nuts. My impact wrench puts out 600ft lbs of torque, so this creates a mild problem if I want to use it to install lug nuts. To counter this problem, I have a set of "torque sticks". What these do is limit the ammount of torque going to the lug. They are in different ft lbs (75 80 100 120 140 ect).

 

A lot of people tend to get lazy and not use torque sticks when they use an impact to put the lugs back on the car. Doing this WILL over torque the lugs and damage them. Basically they will twist a little bit or crack...therefor compromising the intergerity of them.

 

This is NOT a normal thing to happen. I would pursue the last shop that took that wheel off. Make sure you have documented proof of this as well. Where I live, if I made that mistake on a customers car...not only would the shop be liable for it, but I would personally be liable as well.

[outahere]

.......To counter this problem, I have a set of "torque sticks". What these do is limit the ammount of torque going to the lug. They are in different ft lbs (75 80 100 120 140 ect)........

 

I've never used torque sticks because I always use a torque wrench. How do these torque sticks work? How do you know when to release the trigger on the impact wrench?

[broknindarkagain]

Snap On Torque Stick Set

 

I don't understand the exact science behind how they work, but they do work....The way it was explained to me is that the center shaft of it flexes onces the bolt gets to a certain torque. If you look closely at the set, you will see that the extension on each one is a different diameter.

 

If you use impact then torque wrench, you have no way of knowing if its over spec (and probably is). When you set your torque wrench at 80lbs (standard honda torque for a lug) and it clicks right away, its just telling you your torque is at least 80lbs. If you use a torque stick on your impact, it will get it at 80lbs (plus or minus a few lbs). At first I would double check with a torque wrench, but I've never had anything off by more then a few lbs.

[broknindarkagain]

Snap On Torque Stick Set

 

I don't understand the exact science behind how they work, but they do work....The way it was explained to me is that the center shaft of it flexes onces the bolt gets to a certain torque. If you look closely at the set, you will see that the extension on each one is a different diameter.

 

If you use impact then torque wrench, you have no way of knowing if its over spec (and probably is). When you set your torque wrench at 80lbs (standard honda torque for a lug) and it clicks right away, its just telling you your torque is at least 80lbs. If you use a torque stick on your impact, it will get it at 80lbs (plus or minus a few lbs). At first I would double check with a torque wrench, but I've never had anything off by more then a few lbs.

[Shawn06SpecB]

torque sticks have a line down them (ones that I've seen). When the amount of torque exceeds the spec the stick itself will twist and the line will no longer be straight, at this point the lug nut will stop tightening. This is when you release the trigger on the torque wrench...I've never used them before. I always use a torque wrench but these would get you close. It is still recommended to check with an actual torque wrench after.

[SubLo]

When was the last time the car was in the shop with the tires off?

 

Leaving lugs lose will not sheer them off like what happened to you. If they are over torqued however, this can and most likely will happen. Any shop you ever go to will use an impact wrench to remove and install lug nuts. My impact wrench puts out 600ft lbs of torque, so this creates a mild problem if I want to use it to install lug nuts. To counter this problem, I have a set of "torque sticks". What these do is limit the ammount of torque going to the lug. They are in different ft lbs (75 80 100 120 140 ect).

 

A lot of people tend to get lazy and not use torque sticks when they use an impact to put the lugs back on the car. Doing this WILL over torque the lugs and damage them. Basically they will twist a little bit or crack...therefor compromising the intergerity of them.

 

This is NOT a normal thing to happen. I would pursue the last shop that took that wheel off. Make sure you have documented proof of this as well. Where I live, if I made that mistake on a customers car...not only would the shop be liable for it, but I would personally be liable as well.

 

Say what?????? Strain is a form of Shear no matter how you look at it. Strain/Shear forces will be applied to those lugs in a way not engineered. Leaving loose lugs will leave those forces to Fatigue your lugs regardless. Depending on how loose they are and the mass/force applied by the car/ride/bumps will determine how prematurely they fail.

[Max Capacity]

I use my big impact to remove the lugs, then use my 1/2 impact set at 2 to install them, then torque the lugs to 80ftlbs. After I coat the threads with anti-sieze compound.

[ShrinerMonkey]

This is almost always caused by over torquing the lugs. Service shops love to use their air guns without torque wrenches to put on lugs to save time. I have had to stand on a breaker bar to break lugs free on my cars sometimes.