What are the common reasons for a wheel suddenly coming loose?

[Snicklefritz]

As I rounded the corner of the highway near my house, a full-sized SUV was just coming to a stop facing me, minus the LR wheel. By the time I had gone around our block and returned, the driver had is wheel standing beside where it is supposed to be and no sign of a lugnut anywhere. He was mystified. Discount Tires rotated his tires four months ago. He wondered if somebody tried to steal his wheel. He said there wasn’t anything I could do, but thanks anyway, he was going to have his vehicle towed. The edge of the rotor was of course all chewed up. Nice bright chrome wheels, and he obviously keeps everything spiffed up. So, not likely a case of casual/poor maintenance.

Imagining that happening to one of mine and what would explain it coming off like that?

Coincidentally, earlier this year, on the same stretch of highway, not three hundred yards from where this occurred, I saw a 1948 Pontiac Silver Streak with the RF wheel missing, and the driver was collecting lugnuts after retrieving his wheel. He said that he had ordered the "made in China" lugnuts online but must have somehow got the cone shape wrong. This I mentioned to the driver of the SUV, but there isn't any possibility of the wrong lugnuts being the culprit here.

What makes a wheel work loose over a period of months and then suddenly fall off?

 

[JSolo]

Incorrect torque to begin with, or as you indicated, vandalism?

I do recall getting passed by a wheel on the highway years ago. I was bringing the bike back for winter storage, doing ~75mph down I88. Here comes a wheel in the lane next to me... Insane!

 

[Kodiack]

That is why all shops have a disclaimer saying to return in in set amount of milage to retorque wheels, no one does but it keep the liability off them.
That is why I hand torque all wheels to 110lbs...most call for around 90...but I dont want to take a chance.
Most shops dont hand torque they use torque bars.....I dont trust them at all.
I think dodge back in the day had issues with a few of their wheels coming loose because of the alloy they were made of expanded and contracted in heat changes to a large degree that cause lugs untorqueing.
Im not sure how you couldnt feel the rim come loose before it comes off.....but I have never had it happen so Im assuming it would be obvious.

 

[Snicklefritz]

Im not sure how you couldnt feel the rim come loose before it comes off.....but I have never had it happen so Im assuming it would be obvious.

Indeed. I have experienced this exactly once. Years ago, I had a flat repaired at Big O and hadn't even moved a quarter of a mile before I U-turned back with horrible noise and "shimmy" emanating from the wheel. The morons hadn't even finished torqueing it down. I had driven away on an already loose wheel. There is no way that you can lose a wheel without feeling something wrong first. But if the road is bad and your already hearing a lot of noise and feeling the shifting movement, it might mask a wheel coming loose.

 

[Thomby]

That is why I hand torque all wheels to 110lbs...most call for around 90

I would be careful doing this. Lug torque isn't crazy precise, which is why our range is something like 78-94 lbs-ft, but 110 is well above the top end, and bolt torque isn't something where more = better.

Bolts work by clamping two surfaces together so the friction won't let them slip, with the bolt literally stretched like a spring, and rotational torque is an indirect way of measuring that stretch. I believe I've seen estimates of 10,000 lbs of clamping force per bolt at spec (ie 50k lbs per wheel).

Increasing torque increases stretch, and risks moving from elastic deformation (bolt recovers its shape like a spring) to plastic deformation (permanently deformed, may fail). One of the reasons anti-seize is discouraged is not that the nut will back off, but that the reduced friction means by the time you hit your torque spec you've stretched the bolt far more than if it were dry, which risks breaking it.

 

[Grump]

I do my own winter/summer swaps. ONCE I forgot to torque down a wheel and you can definitely hear it. No it did not fall off. I will never make that mistake again. I was young and I probably have 75 swaps under my belt since then, including the wife's car. Torque to spec, check after 100km, after shop visits, before road trips, etc. I keep my torque wrench next to my spare.

 

[LordKOTL]

I do my own winter/summer swaps. ONCE I forgot to torque down a wheel and you can definitely hear it. No it did not fall off. I will never make that mistake again. I was young and I probably have 75 swaps under my belt since then, including the wife's car. Torque to spec, check after 100km, after shop visits, before road trips, etc. I keep my torque wrench next to my spare.

This is the way.