Extended wheel lug failure after less than two years

[cobra]

I don't see why these are failing. In a proper care scenario they should last as long as wheel bolts which are a lifetime item?
Are they being plasticly deformed by overtorquing and fatiguing? Manufacturing issue? Corrosion?

[elbert]

I don't see why these are failing. In a proper care scenario they should last as long as wheel bolts which are a lifetime item?
Are they being plasticly deformed by overtorquing and fatiguing? Manufacturing issue? Corrosion?

One possible reason for the increased failure numbers with screw-in stud is this:
The high strength studs are usually made out of a different material than bolts. In order to have sufficient preload, they need to be torqued at a higher level. However, because of the interface between the steel nut and aluminum wheel, galling occurs. With galling, the friction goes way up, so sufficient bolt stretch cannot be generated, and therefore there is insufficient clamping. This leads to increased risk of fatigue failure.

To overcome the friction issue, you can either apply lubricant to the nut seat (that's what she said) or get two-piece lug nuts.

You can also get press-in (rather than screw-in) studs for extra insurance.
"12mm press-in studs have 44+% larger cross-sectional area at points of peak stress at the hub than thread-in studs and bolts"
In other words, the press-in studs have more material, as the screw-ins have threads cut into them (which are also stress risers).

Core4 can press in for you MSI and ARP press-in studs (the front wheel bearings will need to be replaced), as well as sell the two piece lug nuts.
They also have a lot of this technical info. https://www.core4motorsports.com/

[eacmen]

I don't see why these are failing. In a proper care scenario they should last as long as wheel bolts which are a lifetime item?
Are they being plasticly deformed by overtorquing and fatiguing? Manufacturing issue? Corrosion?

I think I introduced some confusion here and went off on a slight tangent. Apologies to the OP.

OP is using extended Lug Bolts - not studs. Most folks running spacers are using stud conversion kit, which is how this tangent developed.

Screw in stud kits have always been prone to failure and should be considered a routine wear item. Several factors contribute to the failures, most discussed above.

The fact that an extended lug bolt is failing is especially concerning as they are generally considered safer than screw in stud conversions.

[cobra]

One possible reason for the increased failure numbers with screw-in stud is this:
The high strength studs are usually made out of a different material than bolts. In order to have sufficient preload, they need to be torqued at a higher level. However, because of the interface between the steel nut and aluminum wheel, galling occurs. With galling, the friction goes way up, so sufficient bolt stretch cannot be generated, and therefore there is insufficient clamping. This leads to increased risk of fatigue failure.

To overcome the friction issue, you can either apply lubricant to the nut seat (that's what she said) or get two-piece lug nuts.

You can also get press-in (rather than screw-in) studs for extra insurance.
"12mm press-in studs have 44+% larger cross-sectional area at points of peak stress at the hub than thread-in studs and bolts"
In other words, the press-in studs have more material, as the screw-ins have threads cut into them (which are also stress risers).

Core4 can press in for you MSI and ARP press-in studs (the front wheel bearings will need to be replaced), as well as sell the two piece lug nuts.
They also have a lot of this technical info. https://www.core4motorsports.com/

Maybe I am missing something but why are screw-in studs any weaker than a bolt? It is the same thread going into the same hole and there is no feature requiring it to be necked down. The torque should also be the same or very similar since it's the same thread size and pitch.

When I think of galling I think of two similar metals. I've never seen it between the wheel nut taper and the wheel. I was under the impression that interface should NOT be lubed because that friction is what helps keep it from loosening. I do lube the threads for corrosion purposes.

I still think under normal conditions (not overtorqued, not corroding, no weird spacers, etc) the wheel studs and nuts should last a very long time.

[Pklauser]

Bimmerworld response parroted the documentation on their product page. "For simplicity, we recommend that customers consider replacing wheel bolts as regularly as with every brake job."

Now they also pointed out that I was running the 37mm bolt with a 12mm spacer, and that they recommend running a 39mm bolt with that size spacer. I had previously thought that the stock bolt was 25mm, hence my 37mm calculus, but it appears the stock length is actually 26mm. They did say that this difference in length was likely not a factor, but I wanted to share that detail.

The outcome as I see it: I'll be replacing my lug bolts every year now. I like the Core4 idea, but I just put on a new wheel bearings and I don't feel like getting into that again.

[S54330Ci]

Honestly, if you track your car I would swap to studs and ditch the bolts. If you track your car a lot, I would be replacing the bolts or studs every year.

[Pklauser]

Honestly, if you track your car I would swap to studs and ditch the bolts. If you track your car a lot, I would be replacing the bolts or studs every year.

I mainly stuck with bolts because of the alleged reliability. With that out the window, shrug, I personally don't think bolts are more difficult than studs, and they're certainly easier to replace if I'm doing it every year.

If someone gives me a compelling reason, sure, but as far as I can tell it's purely preference.

[elbert]

Maybe I am missing something but why are screw-in studs any weaker than a bolt? It is the same thread going into the same hole and there is no feature requiring it to be necked down. The torque should also be the same or very similar since it's the same thread size and pitch.

When I think of galling I think of two similar metals. I've never seen it between the wheel nut taper and the wheel. I was under the impression that interface should NOT be lubed because that friction is what helps keep it from loosening. I do lube the threads for corrosion purposes.

I still think under normal conditions (not overtorqued, not corroding, no weird spacers, etc) the wheel studs and nuts should last a very long time.

For a threaded fastener to have sufficient clamping force, some bolt stretch is needed.
Screw in studs, because they are typically made of a higher strength alloy than bolts, have different physical properties.
To have enough bolt stretch with higher grade/class metals, you need to apply higher level of torque.
The theory is you cannot generate enough torque because the galling introduces too much friction to get to that higher torque level.
So, if there is too much friction, there isn't enough torque, thus not enough clamping force, which causes fatigue on the stud, resulting in broken stud.

I personally have had some galling, which made me decide to go ahead with the two piece lug nuts.
I found one of my old lug nuts to jog my memory. At the outer edge of the taper seat, there is a narrow band of bright metal, slightly rough with a bit of an edge I can catch with my fingernail.
A minimal amount of material, but apparently it doesn't take very much to make a difference.

[George Hill]

I mainly stuck with bolts because of the alleged reliability. With that out the window, shrug, I personally don't think bolts are more difficult than studs, and they're certainly easier to replace if I'm doing it every year.

If someone gives me a compelling reason, sure, but as far as I can tell it's purely preference.

Ditto, this is the first failure I have seen of a bolt. I wouldn't write off bolts because you had ONE fail.

[Casa de Mesa]

This is a very, very informative video:

https://youtu.be/lK0bzjInqWU

Wheels spacers could be part of the problem.

[cobra]

...
Screw in studs, because they are typically made of a higher strength alloy than bolts, have different physical properties.
...

That all makes sense except for this. Why would a stud need to be made form a high strength material than a bolt? I would think they would use the same material to balance strength and ductility.

This is a very, very informative video:

https://youtu.be/lK0bzjInqWU

Wheels spacers could be part of the problem.

This and elbert's post got me thinking.

When you install a wheel stud, you torque it down into the hub, so no movement is allowed in that threaded joint. We do this so that they can't accidentally unscrew when removing wheels but there's no other real reason for it once everything is torqued. If there is some wobble that develops (due to lack of torque or a wheel spacer issue) it is going to be bending at the highest stress point of the stud - right where it meets the hub threads.

Conversely, if you have a loosening wheel bolt, it's not locked into the threads of the hub and they are allowed to wiggle around and have some slight misalignment due to slop in the threads, and therefore less likely to put stress into the bolt and break.

Maybe? Possibly?

I think if everything is working smoothly and torqued properly, both systems have the same lifespan, but as soon as you get some looseness in there the stud is more sensitive.

[Casa de Mesa]

Have you done the wheel spacer test (video below)? I would also contact bimmerworld to see what they say.

Be thankful you didn't have a moment on track!

https://youtu.be/lK0bzjInqWU

Shoot missed this, scrolled right on by it. I double posted the same vid!

That's what I get for browsing NAM3 while at work.

[Pklauser]

Looking more closely at these extended bolts from bimmerworld...the finish looks sus. Wondering if that delamination allowed water to collect, leading to premature failure.

[Estoril]

Looking more closely at these extended bolts from bimmerworld...the finish looks sus. Wondering if that delamination allowed water to collect, leading to premature failure.

Can we see the two faces of the failed bolt?

[Pklauser]

Can we see the two faces of the failed bolt?

I can grab a more square photo of the one face if the picture in the OP doesn't suffice. The other face is a little mangled now from me getting it out of the hub, but I can grab that too.