i also use anti seize on the lug nuts.
i have extended forged studs and Kics extended forged nuts now, installed them over the winter. i think they should be able to handle 90 ft/lbs with out stretching. maybe i'll just torque them to 85 from now on

 

I got thinking about it, and I am going to disagree with most of the opinions so far, and say that 90 ft-lb is perfectly acceptable. I will also argue that reasonable over-tightening of the lug nuts will result in less stud stretching than an under-tightened lug nut.

Just saying that doesn't hold much merit so I did the math to prove it.

Since they weren't kind enough to list the fastener grade on the hardware, it is reasonable to guess that we are looking at grade 10.9 fasteners which would call for ~85ft-lb to reach 75% proof load. That implies that 100% proof load would be acheived at ~113ft-lb. That is where you could assume that you will statistically expect that you could begin to experience yielding in the threads. To overcome that preload, and increase the stress in the joint, you would need somewhere in the neighborhood of 15,000 lb of force.

F = (113ft-lb)/[(0.2)(12mm)(1in / 25.4mm)(1ft / 12in)] = 14,376lb
Steel on steel -> Torque factor = 0.2

Doing the conversion to the force at the wheel,

Bolt circle force = Wheel force * wheel radius / bolt circle radius
Bolt circle force = Wheel force * (350mm)/(54mm) ~= 7*wheel force

Wheel force for failure if there were only one single bolt --- 2000 lb

That is a bit on the high side for a single wheel, even for an R-compound. Considering there are five bolts and the clamped surface to help react that load, it pretty much rules out overloading as the failure mode.

I would put my money on insufficient torque causing the stretching. It is possible that the initial torque was to spec, but loosened from a combination of vibration and expansion/contraction of the aluminum wheel. Enter fatigue.

 

would heat also reduce the amount of force a stud can hold? did you calculate that in your formula? rotors can see over 1000*, not sure how hot the studs though.

 

OEM all the way. Rust on the hub is a possibility (see below) but the wheels mount up ok (no sticking, can push the wheel over the hub center with no problems).

Nope, Old OEM finish, still in good shape.

It's not the cleanest in the world and has never been cleaned off. As noted above, there's no sticking when the wheel hole goes over the hub but that obviously doesn't preclude a build-up causing a problem someplace.

Anti-seize seems to be a common suggestion all over (I originally posted the question on a local autocross forum). While the nuts go on fine and I see no binding, the dry torque may not be what's needed.

Thanks for the suggestions. It's interesting to note that no one is expecting stud stretch to be an issue...

 

I never said 90 lb-ft was *necessarily* going to hurt anything, the point is there is no BENEFIT to doing so, and over time, overtightening *could* lead to problems sooner.

Speaking as one who *used* to overtighten lugs by 10-15% on my 240Z and had two snap at a track event.

There's absolutely no reason to go to 90 lb-ft on the S.

 

^^^^^^^^ I agree.

Use a torque wrench set for the correct amount (80 ft/lb). Using an antiseize or grease on the lugs will substantially increase the torque applied, I always use dry, clean lugs.

 

Can torquing the nuts while still hot cause the studs to stretch? Reason I ask is sometimes I need to change wheels (almost) right after I'm done running so I can make a ferry. Is this potentially damaging to the studs?

 

Yes. Big rookie mistake at the track is people pitting in after a session and the quickly double checking the torque on the lugnuts. Wait for them to cool off.


Lugnuts should be torqued at ambient temp.

 

Thats what I had thought

How long should I realistically wait?

 

When you touch them and they're not hot?