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My grandson drives a Mercedes 2001 van; the front passenger wheel fell off while driving, but the wheel nuts remained in place, and did not come off. The holes on the wheel had been enlarged enough for the wheel to fall off. What could cause this to happen?

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  • Pls include a photo of the wheel holes if at all possible, thanks.
    – Fattie
    Apr 26 at 10:44

2 Answers 2

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It seems to be an extreme case, but if the lug nuts were not fully secured against the rim, the forces involved in driving can erode the holes in the wheel, especially if the wheel is not steel and is a softer alloy of metals.

In a static position, the wheel stud is resting in the portion of the hole in the wheel farthest from the center. If the nut is not tight, there will be space above the wheel stud. If the nut is partially tightened, it will keep the wheel against the hub but will not keep the wheel from moving around the stud.

As the vehicle travels, each succeeding wheel stud moves as far away from the center of the wheel as possible, simultaneously as a diametrically opposite wheel stud is moved closer to the center of the wheel. This rotation causes the space also to "relocate." The space does not really move, it's the wheel that moves, wearing against the wheel nut, wearing the smallest amount.

At normal travel speeds, this is thousands of times per trip. Eventually the wear becomes so great that the movement is increased, along with the acceleration of wear. A "sensitive" driver would have noticed changes in handling, especially while cornering. It should have been detected earlier as you've noted it was a front wheel and should have been felt as a vague feeling in the steering wheel.

typical lug nut profile

This image above, from carid.com represents a common profile for a wheel lug nut. The taper must be a matching type, presented in this image below from drivenproducts.com:

lug nut seat types

Overlooked in my answer is the possibility that there is a mismatch between the lug nut facing and the wheel facing types.

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    If the operator is enjoying a period-appropriate melody for his (possibly young) age, one might think hearing anything else is excluded.
    – fred_dot_u
    Apr 25 at 13:07
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    I've been in a vehicle which had loose lug nuts and you wouldn't hear them doing anything unless the vehicle was turning. Then it sounded like a bad CVJ. Apr 25 at 15:30
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    @Fattie I suspect there's more to the story than Grandpa knows...
    – SnakeDoc
    Apr 25 at 19:25
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    right, but per the OP "the wheel nuts remained in place, and did not come off. The holes on the wheel had been enlarged enough for the wheel to fall off". This seems incredibly unlikely, really it seems impossible. We talking about the bolts wearing away the actual wheel, and doing so in such a consistent manner that all five holes in the wheel literally become about three times their usual diameter. (Indeed, all the while not actually simply wearing away / snapping the bolts! It seems impossible.
    – Fattie
    Apr 26 at 10:27
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    Regarding an incorrect seat shape. It's a good point, but don't forget nothing's turning, it would just be stuck there at a frictiony point. General vibration could cause some wear or scratches underneath, but the idea that the seat could totally wear through about 1/2 inch of some sort of metal, and then enlarge it a bit more so that the nuts go right through, seems incredible.
    – Fattie
    Apr 26 at 10:33
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"wallowed"

Amazingly to me, it does seem to be a thing that, if you drive with the lugnuts not correctly tight, the holes can be deformed / enlarged / oval-ized a bit.

The usual mechanic's word for this seems to be "wallowed" (various spellings).

examples ... example example

If you type exactly this in to google:

"car wheel bolt holes wallowed"

you may find some information.

To me it seems incredible that the holes would wallow-out so much that they would, all five, be uniformly bigger diameter than the actual nuts, and all of this without destroying the studs or the vehicle being totally inoperable anyway.

I'd say any copper would suspect some sort of crime or bizarre prank or such.

(Random example. A tire store totally forgot to put on the lugnuts, the wheel fell off, and then when the tire store guys ran over to see what happened, someone quickly screwed the nuts on to the now-demolished car whilst yelling "wow the wheel popped over the lugnuts!" or such.)

Anyway "wallowed" seems to be yoru search term for more information.

enter image description here

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  • Well Thank You so much for all this info, I feel confident your answer is correct.
    – juliann
    Apr 27 at 0:15

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