[flash]

first off, i recommend that everyone get rid of the aluminum lugnuts - they do not last and do not hold the torque as well after years of use - i seem to remember reading that the duty cycle of those nuts was something like 25 times, and then the torque handling capacity went down after that - by now i imagine that everybody has exceeded that



second, my hub thickness on my wheels is greater, so i have fewer threads already - no idea what his wheels are like - this is the critical dimension though - determining the distance from the lug seat of the rim, to the end of the stud will tell you how many threads of the lugnut will engage - i cannot add spacers, as i would not have enough threads left



the formula to determine the minimum number of threads is:



Le=2*At / Kn max pi(1/2 + 0.57735 n (Es min - Kn max))



where:

Le = fasterner thread engagement

At = tensile stress area

Kn max = maximnum minor diameter of internal thread

Ex min = minimum pitch diameter of external thread

n = number of threads per inch



there is a simpler general rule of thumb though, and that is that for fine thread bolts this size, you should have at least the same as the diameter in length of threads to hold torque - that means, given that our studs are 14 x 1.5, that we should have 10 threads for full engagement and torque holding



so, you can just spin the nut down, and if it doesn't rotate ten times, you don't have enough threads

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[flash]

p.s. - the 10 thread minimum assumes new threads on both items, and no anti-seize on either (depending on the bolt, anti-seize can mean as much as a 25% reduction in torque holding capacity - i think on these it's more like 18%)

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[Sho968]

Thanks, Flash & Rustech, safety is my #1 concern, too.



As test fit indicated I was getting less # of turns (WAS=10.5 turns, IS=8.5 turns, both with AL lug nuts) with new wheel, I had ordered 56mm studs (928. prefix; stock is 50mm front) and have them now.

Some parts vendors say 6mm or 1/4" spacers can be used without

longer studs, but I won't take their word for it unless I take my own measurement and find the same. All I need now is hubs off & a press...



Maybe I should also get those steel nuts that I've used on my other Porsches. Then I can uninstall spacers for my original wheel with snow tire without bottoming the AL nut, and get visual confirmation of engagement as well. PCA/NW mandates steel nuts for track events, too.



I hate spacers, too, in aircraft world the spacer offset is known to induce additional bolt bending and reduce apparent bolt strength.

I thought about doing away with spacers, but that meant either modifying the hub (if there's clerance for spindle locking nut) or machining the wheel center for clearance and lose hub cap retension.

Then I found some late Porsches use spacers (or goes back to 930 days?) and 6mm is justified in terms of strength.

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