Tarett Engineering

Also, the reason for the lower that factory torque specs, is that the studs have a dry lube finish on them, requiring less torque for the same clamping force.

Ira

Rob S

Ira,

What wheel torque spec does Tarett recommend for the MSI studs you sell? And do you sell studs for use on 991s? If so what wheel torque specs do you recommend?

Rob

paradocs98

This will officially drive me nuts. (No pun intended.) Why does there always seem to be conflicting info? With BMW, I remember that Turner Motorsport specifically instructed to torque their wheel studs to 16 lb-ft with red Loctite. I trust Turner. But then another well-respected BMW parts supplier recommended torquing their own wheel studs to 60-70 lb-ft. I don't recall which company this was.

Seems we have a similar discrepancy here in the Porsche world. I will ask Curtis at MSI tomorrow. He did tell me, though, that the vast majority of the studs that MSI supplies to race teams do not have the shoulder design. So, presumably, they would be torqued to 15-30 lb-ft. He said that MSI does custom runs for a few customers who desire the shoulder design, but, again, this isn't the norm. Maybe that's why Tarett recommends such a high torque figure for installing their studs--because of the shoulder design, even though they might not necessarily be sourced from MSI. Perhaps Tarett can confirm here.

As for the wheel lug nut installation torque--who knows? Is the Porsche recommendation of 160 Nm for the 991 based on a presumably non-lubed, dry, potentially galling stock wheel bolt? Should it then be a lower figure for these stud kits such as MSI, which come with a dry lube coating? Again, an experienced voice such as the principals at BGB could probably help here.

Tarett Engineering

I’ve spent some time researching wheel studs, and think that both MSI and Top Stud make the best studs on the market. There are other similar looking studs out there for less, but they are not the same. The two are very similar to each other except for the shoulder, which requires them to be installed differently and at very different torque values. MSI recommends 15-30 ft-lbs of installation torque, while Top Stud recommends 60-70. I would expect them to both similar recommended nut torque specs.

I believe that some of the BMW shops were switching between the two manufacturers, which would explain why they have different specs.

I’m not sure why the 991 specs are so high, but I’m guessing it’s based on the bolt and hub materials and finish. If using the wheel studs on a 991 or 981, I’d use the lower wheel stud manufacturer specs for the lug nuts.

Ira

Tarett Engineering

Rob,
I believe that the our wheel studs would fit a 991 or 981. I’ve test fitted them on a 981 hub, but haven’t verified that the shoulder will clear the holes in the brake rotor. It should, but I just haven’t had a chance to test it yet.

Ira

paradocs98

Thanks so much for the input from Tarett. I spoke with Curtis at MSI again yesterday to officially place my order. His installation recommendations parallel those of Tarett. To summarize:

• The standard no-shoulder screw-in stud design from MSI should be torqued into the wheel hub at 15-30 lb-ft, with red Loctite. Curtis says some race teams use as low as 15 or 16 lb-ft, but he recommends around 20-25 as the ideal "sweet spot."
• A shouldered design stud, as a custom item from MSI or as the items sold by Tarett, should be installed into the hub using the much higher torque values of 60-70 lb-ft.
• The no-shoulder type studs are installed at the lower torque values because once they bottom out against the hub and the torque application starts, there is no shoulder to bear the force or stretch of torquing. All of that force is borne by threads instead. Curtis suggests that severely over-torquing non-shouldered studs into the hub during installation can lead to failure, the stud breaking off at the hub face. He also noted, though, that he's not seen breakage with his studs.
• MSI applies a dry-lube finish to their studs and nuts to prevent binding/galling and provide for consistent torque values when securing the wheels. Because of this, the nut-to-stud tightening torque during wheel installation becomes the value recommended by MSI, not Porsche or whatever car in which the studs happen to be installed. For MSI, this value is 90-95 lb-ft. I told Curtis that Porsche had just adjusted their lugbolt torque values upward on the new 991 chassis to 160 Nm / 118 lb-ft. He said that once his studs are installed and in use, the MSI recommended wheel torque of 90-95 lb-ft still stands. The application torque that we measure is just a representation of the ideal stretching of the threads at the stud/nut interface. This stretch has a very specific ideal range, and the lubed finish of the studs allows for very accurate torque measurement, and therefore accurate targeting in the appropriate range of fastener stretch. The OEM Porsche wheel bolts do not have this dry lube finish, and the high torque value of 118 lb-ft helps compensate for the resulting increased friction. Installing wheels on the car with the MSI studs at 118 lb-ft, on the other hand, would over-stretch the threads and potentially lead to failure.

This has been quite the education for me. Again, many thanks to Curtis at MSI for his explanations and information, thanks to Tarett for their info, and thanks to the rennlist community for the previously posted informative threads on wheel stud failures.

Rob S

Paradocs,

I'm sure you'll be fine with your choice and your procedures. After all, stud failures are not "common" and it certainly helps to have the highest quality studs you can get, install them properly, and check the torque frequently. I'm sure it would be good to replace them periodically too, as a precaution.

But I am concerned about MSI's 90-95 ft-lb recommendation, especially for the 991. I think their dry lube on the threads may "consume less torque" (through friction) than no dry lube, as least for as long as the dry lube coating lasts. Typically, about 85% of the torque we apply is lost to friction. But the thread/stud interface is just one of two major consumers of friction during the torqueing process. The other is the interface between the nut and wheel (or between the bolt and its captured thrust washer for a factory setup). In that case, I'd give the factory setup the nod as the lower friction consumer because of its design. So these influences compete. Which one has the greatest influence?

But factory specs are just that -- specs. If you use non-factory parts, you have to start over. The real way to determine proper torque is through testing and measurement. MSI is absolutely correct that there is an optimal bolt stretch that must be obtained at the connection. The measurement we make with a torque wrench is only crude approximation of the stretch because most of us don't have the tools to actually measure stretch (nor would we know what is optimal even if we could measure it). If MSI actually tested a 991 wheel and hub with one of their studs and nuts, and measured the stretch to confirm it's optimal (and did it properly!), then we're fine. If they didn't, then I wouldn't assume that the dry lube coating is sufficient to justify torqueing to a lower level, for the reasons above.

And what about 996s and 997s? That's what most of us have. I don't believe that their hubs and wheels are significantly different from a 991 (and Boxster/Cayman) such that it would explain why Porsche raised the torque spec to 118 ft-lb. for these later cars. The factory wheel bolts are the same across all the models and years of 996s, 997s, and 991s. We don't know why Porsche raised the torque spec in 2012, but I could guess

Also, in my experience, the worst possible failure mode is fatigue, which happens slowly, over time, as a crack forms and grows. It doesn't require a big overload, and it doesn't give any warning of failure. To my knowledge, that's exactly the mode of failure that has been most commonly experienced here (and, I might note, I have no knowledge of any MSI studs failures). And bending fatigue usually happens because of insufficient torque or bolt stretch. I would not be so worried about overtorque. It tends to be far more benign -- it will usually manifest as an immediate failure of either stripped threads or a broken bolt (or stud). If you overtorque to a harmful level, you generally know it right away and can sense yielding or fracture. But if you have a fatigue crack growing from undertorque, it festers in your hub, unbeknownst to you, until, perhaps, your wheel falls off, or the stud twists off at the track when you go to torque your wheels.

My point -- it's generally safer to err on the high side, not the low side, of torque. I'd like to think that MSI has really done the math on this and that they're right. But I'd like to see it spelled out in more convincing detail. Does someone know Curtis at MSI well enough to ask him to post a response to this thread? I have nothing but high regard for him and his product, but I'd like to see him respond for all of us to see, if he could take the time. I've been geeking out on this for far too long now.

Rob

paradocs98

^Great discussion. I understand many of your points. And, based on the information in the two big rennlist threads on wheel stud failures, it would seem that the consensus is that undertorquing can more often lead to fastener failure due to the effects of small movements over time.

But, then, the question obviously becomes what is the ideal torque range / fastener stretch for each scenario so that we know what to aim for.

It is curious that Porsche increased the recommended torque value from the 90-range to 118 lb-ft with the release of the 991 chassis. It's not as if the 991 represents a dramatic departure from previous 911s. It's still in the same ballpark for weight and power--it's not a 3900 lb, 600 hp Nissan GTR. And I wouldn't think the new recommendation has anything to do with Porsche reacting to wheel stud failures experienced by enthusiasts on 996s and 997s who have done aftermarket wheel stud conversions. There are too many variables at play to think that Porsche would change the values for their own wheel bolts based on failures of aftermarket wheel studs of unknown origin--were the aftermarket studs installed properly, did they have a lubed finish, did someone use the wrong thread pitch, are the threads cut instead of rolled, are the studs made overseas using cheap materials and processes?

Even so, and as you stated, I would think that once a quality aftermarket wheel stud is in use, the torquing / fastener stretch values then become what is ideal for that particular fastener, regardless of whether the car is a 991, 996, 981, etc. This is specifically what Curtis told me in our conversation the other day.

You can certainly reach out to Curtis by phone to get more info. I don't think he would necessarily respond by posting on this forum--based on our phone conversations, he strikes me as charmingly old-school. I mean that in the best possible way. He seems very honest and straightforward. And he seems to focus on his product and manufacturing rather than social media and forum posting.

In any case, Curtis did tell me that I could contact BGB and Fall-Line to seek their input on torque values, since they use MSI studs. So I'll do that this morning and report back.

BGB Motorsports

Ladies and Gents,

Sorry for the lapse in responding. I don't know why but when I get a PM on Rennlist, I don't get an email update. If you are the same gent that emailed me earlier, I will send you an email separately.

As for the discussions and what has worked and has not worked in the past, I found Curtis at MSI almost 5 years ago because it was getting harder and harder to find QUALITY motorsport Porsche wheel studs. The ones that I did find had two types of thread one one stud, one of which was rolled and the other tapered partially and I threw my hands up in the air and went to the source, NASCAR country. At the time, Curtis was breaking out in the sports car world from NASCAR and since Curtis makes parts for the big boys that make 900hp and go around 31 degree banking and even worse, can survive Martinsville, that was enough for me. Since meeting Curtis and now partnering with him as a sponsored team, we have 5 seasons of racing under our belt running 2-3 cars and a quick 24 hour race; Curtis makes wheel studs for a series where pit stops are everything and mistakes have no room. No MSI part has EVER EVER EVER failed on our cars and that's an extremely hard earned distinction in this arena. The one failure we had occurred when one of my techs had never changed a tire and he rounded off a wheel nut when he put an air gun to it that made 300psi of nitrogen on the other end. IN THE MIDDLE OF A RACE...we managed to get the stud back out and another one under yellow. We then proceeded to lead the next hour of the event because we were able to rebound quickly (Road America 2013 - 1 more gallon and 4th would have been 1st...oh well!)

I live and die by 95 lb/ft. Someone posted install instructions and I cruised over those and they seem to be on point. The two danger areas are as follows:

1. Make sure your lug nuts and your lug sockets match up.
2. Be careful not to "mushroom" the hub by threading in the stud too far. When it gets hot the ears of your hubs will grow and rub on the inside hat of your brake discs. If you are really really concerned, run some blue Loctite but be careful because you can thread them in "too far." If they have a shoulder, it's easier to know what is too far and what is not.

I live and die by factory torque specs and when we endurance race cars for 24 hours, we bump the factory numbers another 10% sometimes. I would not be uncomfortable telling all of you though to run 95 lb/ft. I would however be uncomfortable telling you guys to torque stuff to 115lb/ft. The only difference between MSI and the rest is that you can probably torque alternative aftermarket nuts and bolts to 115lb/ft...ONCE before SNAP!

P.S. The car in the avatar to the left was my 991 that sported Curtis 100mm wheel studs. The car did 4 days at Daytona, 2 days at Barber, 2 days at Road Atlanta, 2 days at Watkins Glen and 30,000 miles on the street WITH double stacked 15mm hubcentric spacers adding 30mm of track. Our GX race car survived Watkins Glen and Daytona 24 with the same HUGE double stack of 15mm hubcentric spacers. NO FAILURES! If that's not enough test data, I don't know what else is.

paradocs98

Just what we were looking for, John. Thanks so much. Can't get a better endorsement than that for MSI.

I don't fully understand your warning about mushrooming the hub by threading in the stud too far. Can you describe this further, or in different terms?

I installed my non-shouldered MSI studs using Curtis's recommendations. I used red Loctite, and was able to get anywhere from 15-20 lb-ft on the studs during installation into the hubs. I couldn't generate any more torque than this because the doubled nuts started to slip on each other, despite my efforts to lock them together. The point where the studs "bottomed out" into the hub during installation was pretty obvious; it was at this point that torque began building during further screwing into the hub, until 15-20 lb-ft was hit.

I was happy to get the 15-20, and I can't imagine tightening so much further that you would end up with the studs in too far and causing this mushrooming effect. Would this excessive depth only be caused at really high torque values like 50+ lb-ft?

BGB Motorsports

I kept thinking about all of this on the way home. If you were to torque an MSI combo wheel stud and nut to 115lb/ft., you always run the risk of loosening the stud in the hub when you go to take off the nut. DO NOT subpoena me if someone has a failure and wants to say that they should have torqued them to 115 lb/ft! I'm going on record that of the last 10,000 times I have made my crew take tires on/off, we torque them back to 95lb/ft.

As for my warning, if you have the larger shoulder version stud that Curtis made for me with the beefy shoulder then it's harder to have the "mushroom effect."

In reading your post though, I can tell that you're clearly plugged into what you're doing. You have the version without the shoulder and were able to tell when the torque ramped up. Sometimes people don't and we all make mistakes as we are all learning. Continue the good work...if you have any more questions, don't be afraid to send me an email and even another if i don't get back to you. If it comes to something like this where safety is a concern, you can even just call the shop and ask someone to leave a message for me.

flink

After installing bullet nose studs I always cut witness marks into them with the dremel cutoff wheel so I can see if they ever rotate. Cut parallel to the stud, facing the hub.

Jnosol

Great old thread here, thanks. I did all my homework and MSI is the best wheel studs for the money. ARP is better, but I don't think they're double ended and cost 2x more.

My 991 GTS non-CL will be fitted with Signature Wheel SV102 soon. Need studs as the OEM wheels have 5mm spacers.

I'll summarized it for other 991 owners looking:

• MSI's studs are 4340AQ chrome molly steel, made in the US and supplier to NASCAR
• Most will only need the shorter of the 2, 82.5mm
• Just buy R14 OEM style nuts, if you use any good custom forged wheels made for Porsche they will drill the holes to match R14 seats
• Torque MSI studs to 20-25ft-lb only since it's not the shouldered design
• Torque the wheel nut to 90-95ft-lb as these studs are lubricated, requiring less torque than OEM