Educate me on wheel stud failure.

[BonzoHansen]

Local guys are discussing wheel stud failure because one of the younger guys lost a wheel and it got me to thinking about reasons why. I put this together based on my experience and what I think is common sense. Can any of you smarter types tell me where I am wrong/right? Considering the safety aspect I figure it is a proper discussion here.

*Lugs not tightened enough (I bet the #1 reason)
*Lugs overtighted/studs previously stressed (I bet a very close 2nd). I'd think this will also over stress the head (flange) of the stud, weakening it.
*Lugs not tightened in proper pattern
*Lug nut wrong seat (common with replacement wheels, esp aftermarket)
*Wrong lugs (ie metric nuts on SAE threaded stud)
*Not enough thread engagement (common with replacement wheels, esp aftermarket)
*Previous rim damage (nut seat damage, non-hub centric makes it worse)
*New aluminum rims not re-torqued after a few 100 mile cycles. (seen that)
*Wheel not properly seated at time of mounting, perhaps due to corrosion on wheel and/or mounting surface preventing proper seating. And aluminum wheels corrode too, or wheel not fitting properly over hub (esp w/aftermarket wheels)
*Improper installation of stud (ie with impact gun instead of a press)
*Hub/flange failure due to improper/oversized studs being installed
*bolt pattern mis match (ie BMW wheels on a Camaro)
*Cyclic, fluctuating loading - why the drag guys running such grossly oversized wheel studs to compensate for the shock loading at launch. Under-torqued lug nuts will almost immediately see fluctuating loads and lead to premature failure
*Too much HP
*manufacturing defect (poor hardening, etc)

[oestek]

Improper lug nut depth... I've seen people tighten nuts, only to be tightening the cap of the nut on the stud, and the wheel isn't even squeezed! Always measure the depth of the nut on cap styles and make sure the stud length allows the nut to tighten on the wheel!

Good post, BTW!

[Apogee]

You rattled off most of what I could think of and I agree that under-torqued lug nuts (whatever the cause) are probably the number one reason for failures. The wheel studs never see any additional load or stress other than the preload stress set by the lug nut torque unless those preloads are actually exceeded by the external loading. That means that your wheel studs should have a fixed loading scenario 99% of time if sized properly. Cyclic, fluctuating loading scenarios don't make for happy wheel studs, hence the drag guys running such grossly oversized wheel studs to compensate for the shock loading at launch. Under-torqued lug nuts will almost immediately see fluctuating loads and lead to premature failure.

Wrong wheel pattern is another one, i.e. 5x4.75 versus 5x120mm. Wheel studs are meant to be in pure tension...throw bending into the mix and you significantly reduce the factors of safety built into the wheel studs, especially if you like to torque to 90% yield as calculated by tension only.

Tobin
KORE3

[DynoDon]

One of the guys at work broke some studs and lost the wheel due to tire shake. They were Titanium Studs with Encapsulated Aluminum Nuts - and a 2700 HP SBC

[BonzoHansen]

Tobin, along these lines on bolt pattern:

Guys,
Lately I've been reading about some people using BMW wheels on their cars which have 4.75" BP hubs & axles. I understand BMW wheels are a cheap, durable alternative to aftermarket wheels and many styles look pretty good.

I was bothered by the mentality that BMW's 4.72" BP was "good enough" for the 4.75" hub. The fact is we're talking about the 5 fasteners that attach wheels to the vehicle; we've seen these studs break from fatigue using wheels with the correct BP. Turns out, this "minor" difference in BP bends the stud at a 0.53 degree angle. Now we have a situation were the stud, designed ONLY to be in tension, is undergoing combined stress (tension and bending) during the assembly procedure. This is not good!

So I did a little FEA simulation to see what kind of difference this is going to make. This analysis only shows what the stud is undergoing after the lug nut is torqued. This does not show us:
1. “Twisting” stress from torque applied to the stud;
2. Stress from driving the vehicle;
3. Fatigue over time.

Please note these three situations will make the results worse. Here we go:


Here is the stud using a 4.75" BP wheel. Note the stress concentrations at the chamfer resulting from 10,000+lbs of tension. These results are typical.



Here is the same stud using a BMW wheel. Note the larger stress concentrations resulting from bending stress, and the stress continues all the way up the shank. This photo shows the stud being bent away from us; the other side is in compression and results in a stress concentration higher up the press-in shank (about where the threads start). Stress has increased by a little over 20%. That's a significant increase. Again, accounting for fatigue and torque-related stress will further reduce the stud's service life.

I'm not trying to rain on anybody's parade about using BMW wheels, but I feel this is something people should know when making a decision on which wheel to use.

[Mingus]

Not being hubcentric is probably a cause of a lot of failures because you are asking the lug nuts not only to center the wheel but hold it centered under incredible loads instead of just holding the wheel on the hub.

[CamaroAJ]

metric nuts on SAE threaded stud. i've seen that before come into the shop with loose wheels.

[Apogee]

Not being hubcentric is probably a cause of a lot of failures because you are asking the lug nuts not only to center the wheel but hold it centered under incredible loads instead of just holding the wheel on the hub.

Interestingly enough, hub-centricity probably isn't as big an issue as some might think. Regardless of hub-centric or lug-centric, the wheel studs are responsible for holding the wheel in place, they really only differ primarily in installation.

There are plenty of factory applications that are not hub-centric as well as aftermarket wheels. Ideally, everything would be perfectly centered, however that is the purpose of tightening the wheels in a criss-cross pattern incrementally so that all of the lug nuts can seat properly, centering the wheel in the process within a few thousandths of an inch. I haven't done a comparison between the two methods specifically with respect to wheels, however with rotors it is easy to reduce the measured runnout by about half going to a snug hub-centric fit versus lug-centric keeping everything else the same. Thte same principles should apply to wheels.

Having a hub-centric wheel just means that the wheel is basically centered to begin with, minus whatever the radial clearance is for the slip fit. Once the wheel is clamped to the hub, the only way that the center hub-centric register will ever see any load is if the wheel studs/lug nuts are not doing their job and allow the wheel to move...which shouldn't happen except in extreme situations like described above with too much tire/HP/etc.

Oddly (to me anyway), heavier GVWR rigs like 3/4, 1-ton trucks are mostly lug-centric last I checked, as are my 1/2-ton axled rigs. This could be due to the fact that the unsprung weight on these rigs is so much higher that a little imbalance at the wheel doesn't negatively impact the handling of the vehicle like it could on a modern import or domestic car.

Tobin
KORE3

[sik68]

A classic:



I heard Metric vs SAE

[Skip Fix]

Not being hubcentric is probably a cause of a lot of failures because you are asking the lug nuts not only to center the wheel but hold it centered under incredible loads instead of just holding the wheel on the hub.

Also having a short axle hub not to engage the wheel. Currently I have some factory hubcentric 81 Trans Am Turbowheels that are on Moser axles that barely protrude out the rotor. The correct lugnuts are not completely locating the wheel as I can see it move as I spin it when they are close to snug. It would cause shake as the wheel wouldn't be centered if I drove it-they are just on to push it around the shop. Hopefully the drag wheels an lug nuts will locate it better.

[DynoDon]

What me worry?

[Dstoltenberg]

What about running hub-centric and wheel-centric wheel spacers with longer studs?