Wheel stud kit on order ... now worried about them breaking on the track?

[Maxhouse97]

Got my MSI studs from Turner, but it did not have any installation instructions. Was going to call them tomorrow, I know about red loctite and double nut, just need the torque. I think other studs are around 25 ft-lbs.

[Nick_P]

Got my MSI studs from Turner, but it did not have any installation instructions. Was going to call them tomorrow, I know about red loctite and double nut, just need the torque. I think other studs are around 25 ft-lbs.

Apex studs were between 22-25 ft-lbs and the nuts between 85-90 ft-lbs. Not sure if MSI are the same though

[r4dr]

Turner should have installation instructions on hand to send you even if they didn't include them at first.

[Maxhouse97]

Got these installed, look great.

[gills]

Hello all, Tom from Core4 here. This is my first post so I apologize that it's a long one! And it's sort of technical, so sorry for the boredom.

I just wanted to chime in here for obvious reasons. I appreciate those who've shared the Core4 solution and of course I understand the apprehension to it as well. It's different, but not really (as already mentioned, other OEM's, etc.) so in reality it's not outside of the box at all.

The science and engineering behind nuts and bolts is anything but simple for something seemingly so. Just to be clear, I work very closely with MSI on all of this. MSI is purely a manufacturer. They don't do any engineering in-house such as a huge fastener company like ARP does.

They do have 25-30 years experience making wheel studs and nuts and they make whatever customers want them to make and in small quantities (how they differ greatly from ARP and why they have a stronghold in Motorsports). The studs and nuts they offer now is basically what NASCAR, and then later on, what professional sports car racing teams had them converge on. There are some things I truly believe they can actually do better and I'm in the process of getting them to make those changes, at the very least for the studs I offer. As someone mentioned, I claim that some of the studs on my broken stud gallery page are MSI studs, and that is correct, there's a few. I can forward you to the people who shared those broken MSI stud incidents with me if you'd like. Virtually every popular brand of stud is depicted on that page.

I am a mechanical engineer and I've done (and am still doing) quite a fair bit of research, as well as torque-tension testing on mock hub-rotor-spacer-wheel setups, which also included high temperature testing and effects of thermal expansion. I've also been collaborating with a fastener specialist (Dr. Bill Eccles, PhD) who is a genius on the topic. As an example, one of his projects was contracted by the UK government to determine the root cause for excessive wheel detachments (i.e.-losing a wheel on the highway) in the commercial trucking industry in the UK/Europe several years ago.


So there are a few points that are constantly spread in paddocks about wheel studs that I feel like need to be addressed.

1. The single most important thing that a stud/bolt needs to do is clamp what it's holding together as tightly as it can, regardless of press-in or screw-in. This is known as preload or clamping force.
   
   The sole purpose of moving to a higher strength/class/grade wheel stud/bolt is to have the ability to clamp the components together more tightly. Engineers deal with this design problem all the time. Move to a smaller diameter, higher grade fastener, or go with a larger diameter lower grade fastener in the design. In the case of the smaller diameter, higher grade fastener, setting the necessary preload becomes more critical.
   
   Studs/bolts have to clamp these components so they can never separate from each other when external loads are applied to it (lateral and longitudinal accelerations, brake and and engine torque, road bumps, and any combination thereof.). What's not intuitive is that the tighter a stud/bolt clamps what it's holding together, the less of the external loads it bears. As soon as this clamping force is over come by external loads, "joint separation" occurs, where clamped components can potentially move relative to one another, the studs sustain 100% of the external loads. You never want this to happen as the stud/bolt will undergo extreme bending stress and WILL ultimately fail from bending fatigue.
   
   Bending fatigue failure of studs looks exactly those in the picture that Estoril posted on page 1. His description of rust forming is actually very common, as these cracks form in the root (valley) of the thread and they can slowly propagate/grow through the cross-section until the cross section can no longer sustain the loads and final rupture happens. You can't see the cracks with the naked eye. The only way to determine if cracks are there is with some form of penetrant testing.
   
   The fracture faces on those studs in his post is NOT the fracture face of being over-tightened or overwhelmed in tension. Fasteners that are over tightened stretch considerably, and if they truly fail from being overloaded in tension from in-service loads, the fracture face typically has a ~45 degree facet when looking at them from the side. This is very rare with wheel studs because the "wheel joint" is one that has a significant safety margin, for good reason.
2. Which brings me to the belief that "it's very easy to over torque-tighten wheels studs" and that being the typical cause of failure.
   
   This is demonstrably false. By far the vast majority of wheels studs that break are bending fatigue failures which is due to a variety of reasons all related to insufficient clamping force. That can happen from insufficient tightening torque, excessive friction while tightening, self-loosening, thermal expansion loosening, "preload relaxation" and "embedment loss," to name the most common. It just so happens that screw-in studs are much more sensitive to bending stresses since they have stress risers at the point of highest bending stress in this application (where they screw in and bottom out at the wheel hub). A fundamental difference between them and press-in studs.
   
   In fact, it's exceptionally difficult to overtighten and actually "over stretch" studs. This is especially the case with any grade 8/class 12.9 wheel stud, even a 10.9 (OEM). There's very important factors that most overlook and they both relate to friction.
   
   First, is that a lug nut is almost always a 60 degree cone/tapered seat. We're all used to thinking of nuts and bolts as having basic flat surfaces that spin against each other. We even look up values on torque tables that were derived using basic/standard nuts and bolts to torque our lug nuts to. The glaring difference here is that the 60 degree geometry of a lug nut is essentially a wedge as it's being tightened into a wheel seat and this wedging effect generates twice the amount of friction than a standard flat nut would.
   
   The second is the material in which it's rotating against, in this case, aluminum (wheel). Aluminum is soft and gummy in the metallurgical world and galls easily (welds itself to the opposing interface) when subjected to the pressure and friction of the lug nut face rotating against it. This creates even more friction. All this extra friction dissipates/takes up the majority of the torque you're using to tension the stud, instead of tensioning/preloading the stud itself. So what you think you're tensioning the stud to is much further off than you think. We're talking 1000's of lbs off where it needs to be and can vary 1000's of lbs in each subsequent tightening cycle.
3. "Don't touch the lug nuts/studs with the car hot"
   
   There's truly zero evidence to back this up other than what people chirp at the paddock because of what might seem like intuition and paranoia. There is far greater risk in not checking your lug nuts with things hot and risking low preload/tension/clamping force than there is with putting a torque wrench on a "hot" setup. And if one does break when checking torque or changing wheels in between sessions, consider yourself lucky since you've found one with fatigue cracks in it prior to all of them letting go on track.
   
   Quality wheel studs are made from alloy steel. Alloy steel doesn't lose any notable strength until 400F and even then it's not as much as you think. I assure you that your wheel hubs, studs, and lug nuts are not getting this hot. If they are, you have other problems.
   
   What elevated temperatures does is affect preload due to thermal expansion, and not in the way you think. I've done testing with a mock wheel joint assembly; center section of an Apex BMW wheel, 12mm concentric spacer, 7-8mm thick rotor hat, wheel hub, press-in studs and lug nuts tightened to common values with standard lug nuts (no lube). I then heated the assembly in the oven for an hour at 350F.
   
   I did this in three different scenarios:
   1. The whole assembly at room temperature and fully torqued prior to heating (simulate start of the day).
   2. Heating everything together not torqued and then torquing after pulling out of the oven (simulate hot wheel rotation).
   3. Everything heated except the wheel, then I torqued the room temp wheel on the hot everything else (simulate wheel change on a hot car).
      
      Never once was there an issue of increased preload/tension at the elevated temperature and when cooled back down to room temperature. In fact, there were instances where preload was lost.
      
      In some tests, I checked to see if I would get any extra lug nut rotation at 90 lbs-ft when I first would pull it out of the oven and more often than I was expecting I would get rotation on some. Even in those cases of extra rotation with it all hot, once everything cooled back down, there was NEVER extra preload on the stud. I was doing this by measuring the elongation of the studs with a micrometer.
      
      I emphasize the last point because basically everyone believes that thermal contraction of the wheel will create an extraordinary amount of extra tension/stress on the stud if you had tightened the stud when everything was hot. This is simply not true.

Sorry as this is a lot to digest so I'll leave it at that. There's always more to add, but it's already long enough. If you want to discuss any further, please feel free to PM me or email me at core4motorsports@gmail.com and I'll be happy to talk.

[foolio]

Hello all, Tom from Core4 here. This is my first post so I apologize that it's a long one! And it's sort of technical, so sorry for the boredom.

Thanks for the detailed post. Not boring at all! I appreciate the opportunity to be enlightened. I have definitely been one of those “don’t touch the wheels hot kind of guy”. One question that keeps coming up is replacing studs preventatively. Can you give any guidance on that? I am sure it depends on how they are being used but perhaps you could give some examples. Also, what can be done about galling and ensuring we are getting the correct clamping force? Is some sort of lubricant on the conical face of the nut recommended?

[Maxhouse97]

Thank you for the great post! My takeaway is the most important piece is to keep your lug nuts tight. Makes sense to me.