It is not the metal fatigue life in this example, it is the ultimate tensile stress. Driven on the street, the stresses are less. As soon as you hit the autocross course, the stresses increase to the point where the studs break. If one stud lets go, the stress on the others increase, snapping them immediatly. Don't forget the jolt on the car as the first tire fell off. That jolt gives a momentary spike in the stresses of the other studs. It is most likely that all the studs were made in the same batch, so the UTS would be very even.

What I find astounding is the fact that the owner of the car above (worth how much?) is thinking of cheaping out on wheels. I would expect that from a Hyundai or Kia owner.
Work a few hours of overtime. Sell some of the junk in your garage on eBay.

That video - the problem was probably with the wrong sized lugs, or the wrong thread, and he cross-threaded them, thinking they were torqued. The studs don't carry the loads - the lips do (in most cases).

-Wayne

"It is not the metal fatigue life in this example, it is the ultimate tensile stress."

The lug studs are in shear, not tensile unless the lug nuts were overtightened. I still say the odds of 16 studs breaking at the same exact time are beyond my counting ability, but I could still be wrong. It wouldn't be the first time, nor the last.

"the problem was probably with the wrong sized lugs, or the wrong thread, and he cross-threaded them, thinking they were torqued. The studs don't carry the loads - the lips do (in most cases)."

I'll have to give the owner some benefit of the doubt that he didn't cross-thread all the lug nuts or that he sourced 16 incorrectly-sized nuts, but they don't present annual Darwin Awards w/o due consideration. I would think this would minimally be the second time the owner installed the wheels. IMHO, 16 cross-threaded nuts aren't going to come off that easily nor simultaneously. I think this might have been a case of someone hand threading the nuts, maybe about 2 threads worth, to be tightened with an electric impact gun later, but overlooked. Basic wrenching technique suggests tightening threaded fasteners once started so as not to overlook later.

Maybe we're watching too many Hollywood movies and not enough Mythbusters? :)

Sherwood

On the lugs I would vote they had the wrong lugs, like used conical lugs on ball seat wheels or oppsoite this would cause the wheel to get loose, I have seen this way to often where people dont realize the difference, Kevin

If given the choice between spending $7000, (1400 x 4, tires for 1200, plus mounting, 200) for wheels and tires, or $4600 for Chinese knockoffs of same, (both for presumably cosmetic reasons) or a trip to Italy, I'd agree with your wife! (Sorry, I'm not helping, am I? ;) )

The story we got from our SCCA region director was that the lug nuts were not the correct thread for the studs... that they went on and were tightened down, but that when the car went out for the AX the additional stress ripped the threads from inside of the lug nuts.

Probably related somehow to the fact that an SAE -20 is almost exactly the same pitch as a metric -1.25.

Almost.

cashflyer your saying they used gm truck lugs, Kevin

I don't agree with that. When you tighten the nut down on the stud, the stress on it is axial (tensile). If the nut is tight enough, the stud sees hardly any shear, since the friction between the wheel and hub takes the shear force. FWIW...

ianc

True, but the situation as was presented suggested the cross-threaded lug nuts were not clamping the wheel or they were with rapidly diminished effect. If so, the vehicle weight would have been supported primarily by the studs .... and in shear.

Sherwood

Mostly, China is where the US was in the 1890s and the Japanese were in the 1950s...

there are pockets of high-tech and super-quality in China but you have to search them out.

Meanwhile "It's very well made in Taiwan..."

this is the second time I heard this, which makes me a little worry. can I ask what type of seat the CCW wheel is? Is it the same as the stock Fuch wheels? I am using my black nuts on CCW wheels. Is it ok?

$999 for a set of 18 inch wheels . . . *with* tires?!?

sometimes I even see less than $400/set (no tire of course), same brand and look the same as the set is selling for $900. I bet they are the same. It's the ebay thing.

Okay guys thanks for the feedback, as usual great insight.

I guess I’ll have to sell my porn on e-Bay to pay for the wheels. This way the wife approves of the way I spend money.

So I have narrowed it down to two HRE wheels. I’m leaning towards the 647R, (first photo) with the 447R (second photo) as a second choice. What do you think?

Stay safe everyone and thanks again.
http://forums.pelicanparts.com/uploa...1208066651.jpg
http://forums.pelicanparts.com/uploa...1208066666.jpg

Just very personal opinion. I think the first one look better. The second look a little older style.
Do they have the right offset?

I kinda like the factory wheels...

Keep what you have, and go back to Italy!