froggy47

Autox this weekend & we had 2 different cars with complete failures of studs. Sat was a light weight open wheel formula car and Sun was an Elise.

No reason to think either car was not well prepared & I know both drivers.

My thoughts are that many "parking lot" courses have some rather serious bumps, patches, drainage features that cause extra sheer stress to lugs, compared to the rather smoother track surfaces. Speeds are slower in autox but 70 - 80 thru a bad bump is not unusual.

I recently did my rears & am now going to do fronts (arp).

I hope we all put new nuts on every year, but the studs apparently need some attention also. Maybe not yearly but I don't think they last as long as the wheel bearing. Maybe every 2 to 3 years for studs. My fronts are original on a 2004 so I think they are due.

Especially if you have multi sets of wheels & change them often every time you torque them you are stretching the stud.

My 2 cents fwiw.

c4cruiser

I would think that the event planners (especially the course designer) would design a course that would at least try to avoid bad spots in the pavement. With those kinds of speeds you mention, bumps and holes on the course could lead to damage to not only studs, but tires and suspension components.

Replacing studs and lug nuts on some sort of a regular basis is good preventative maintenance especially when it comes to competitive events. As you mentioned, regular swapping of wheels can lead to stretching of the stud and the threads will show signs of wear after some time. Proper torquing of the nuts is important too; both by the proper sequence and the correct torque value. Lug nuts are fairly cheap if you are using a stock style lug nut and a new set each year wouldn't break the bank.

I just replaced an OEM front hub on my 87 and after 5 years worth of using A6's on the car, I was really surprised to see those original studs in decent shape. I did replace the studs on the front hubs with ARP studs, and in the next month or so, I'll be doing both rear hubs and adding ARP studs to them.

davidfarmer

I continue to be convinced that many,if not most, stud failures are due to over-torquing at some point in the studs life. You can safely torque as low as 78 ft-lb (OEM on some cars), but anything over 100 ft-lbs will permanently distort the stud (in most cases, depending on size etc). I often see people torque until they hear the "click", then push it just a tad beyond........ Might as well not even use the torque wrench!

Solofast

Overtorquing will break a stud every once in a while.

What breaks wheels off of cars and breaks all the studs at once is usually undertorque (forgot to torque one wheel, or all wheels after a tire change), or improper fitment where the wheel isn't seated properly on the hub and it ends up putting cyclic loads into the studs, or the lugs loosened up (not uncommon at all).

Studs are pretty simple. If the wheel is mounted and torqued properly, there is no cyclic loading, and the studs don't fatigue or break. Put in cyclic loading and they fail in a run or two. You would have to be breaking wheels to have impact loads sufficient to overcome the clamping loads on the studs, I don't think the course roughness has anything to do with it if the wheels are properly tightened.

Proper torque (generally around 80% of yield) does not yield the stud and unless the threads get worn, there's no reason to replace them.

Some wheels require a second torquing after the car has been run for just a bit or they get loose. We generally run the car for a warmup around the paddock or out onto the street after a tire change to settle the springs and get the brakes warmed up. After that we do a second torquing of the lugs to check for tightness. Often I find one or some aren't as tight as they should be (wrench moves a bit before it clicks). Sometimes I don't get a chance to run the car around a bit after the tire change, so I retorque after the first run.....

My guess is that they may have torqued the lugs but they loosened up and that is what caused the problem.

davidfarmer

I agree loose lugs is also a problem. I've done it once in 20 years (never went on track though). I disagree about re-torquing though, especially if you run them enough to generate heat. If they were properly torqued in the first place, they should not come loose.

froggy47

You have no idea how much time we spend trying to put the "perfect course" on the lot. As for the rest, I agree.

c4cruiser

As an event chair and course designer, I know how all that works We use an abandoned runway and there are places that are in pretty sorry shape so it's hard to build a course that flows well yet misses the bad spots. And everyone wants to go fast

UstaB-GS549

Two experiences with failed wheel studs:

A friend used to use electric impact wrench to loosen and tighten studs for a season and had several failures. Mostly from the nut being seized on or cross threaded. the stud broke when unscrewing nut.

Another time was an experienced track rat who got black flagged for pitching lug nuts at corner workers. He came in with 3 missing studs. Looked at he broken studs seemed like a classic fatigue failure to me. He swore that they were all properly torqued. The two remaining lug nuts on that wheel were finger tight.

I have been doing this for 25 years with stock GM studs & have never broken one. All hand tools and 100 ft-lb setting on the torque wrench.

I have seen some people using a torque wrench like they assumed it was a torque limiting device!

Just another opinion.

froggy47

I found some arp's for my front that are 1/2 inch longer than stock. I am going to try to squeeze them in without pulling the corner off. On the rear a few months ago I was going to drill the backing plate to put some 3.25 arps on but I decided it was too bubba and took the corner off, ended up not so bad.

These fronts may squeeze in, we'll see. It'll be on an angle to get it in the hole. I'll shoot a video & add it to the others.



BTW those studs on the Elise that sheared were threaded on both ends so screw into the bearing & then nutted like a Vette. Pretty easy to replace but only 4 studs. The engagement of threads that went into the bearing looked like only 5 or 6 threads. I think the Vette is much stronger design.

fatbillybob

loose nuts = broken studs. I have never seen an overtorqued lug fail in use. They mostly break on the torquing. It is because of the physics of a clamping load. Studs are not really in shear but people think they are. If you are too loose then you have the studs in shear = bad. Galling happens when the size of the stud or the nut is loosing tolerance. You can encourage galling by having unclean studs and nuts. Anti seize should never be used on studs but people do it all the time. These people tend to be sloppy and pick up dirt in the antiseize the next time grinding out the tolerances more each use. They are destine to fail.

froggy47

I used to do clean and dry. The conical contact faces between the lug nut and the rim center developed what I call galling, Bits of aluminum alloy (rim center) became embedded on the iron lug nuts and eventually would have eroded the rim alloy gradually making the hole bigger.

Some aftermarket rims have inserts in this area I think to eliminate the galling but not the stock rims.

Careful & light application of almost any lube (anti sieze etc.) has completely eliminated the transfer.

A similar type "erosion/wear/grinding" was happening between the nut and stud. Usually it was nut metal getting deposited on stud metal.

This may have been exacerbated by "gunning" the nuts on/off at high speed.

I changed technique to the slowest possible speed setting on the gun & light trigger (this is pretty darn slow) and a small dab of lube about every 4th wheel change. Brass brush the threads clean first & brake cleaner then renew light lube.

This is what works for me now for the last couple of years.

Factory torque spec reduced 10%.

FWIW.

If you have more info or reference on clamping load/shear forces especially as regards automotive wheel mounting, I'd like to know more "science" of it. I am sure there is a lot of engineering involved and I'm not one but eager to learn.

mgarfias

If anti-seize on a wheel lug was really a bad idea, so would be 30wt on the threads of your rod bolts. The dirt thing is a consideration, but i'm convinced that a dry lug has uneven friction, and that a lubed lug is more consistent, thus you can get it to your 80% of yield all the time, not just kinda close.

I've had lug failures due to dealerships using impacts and over torquing. I torque to 85lb now, per ARP, w/moly. Haven't had a problem, replace studs when I replace wheel bearings.

UstaB-GS549

Here is kind of the short version:

Torque generates a tensile load (preload) in the stud and stretches it a bit. As long as the forces acting on the stud (wheel) are less than the preload, the load in the stud is static. What this means is that if you torque it to spec and you don't twist the stud off, it will never break while in use.

The studs are M12 and probably Class 10.9 (similar to Gr. 8). At 92 ft-lb torque, each one develops 12,825 lb. of clamping force. So with 5 torqued studs you have about 64,000 lb of clamp force between the wheel and the hub. Assume that you are foolish and decide to grease your wheel hub which will reduce the coefficient of friction between the hub and wheel to about .15.

Force = u * N, where u = .15 and N = 64,000 lb.

F (transmitted force) will be 9,600 per wheel due to friction under the above conditions.

Hopefully, you probably won't grease your hubs and u is going to be more like .45, so that F is going to be about 28,800 lb. per wheel. That how much force it will take to slip the wheel on the hub. Thats why hub centric is nice for hanging the wheel on the hub, but once it's torqued, hub centric doesn't mean much.

But, if you don't torque your wheels, F may fall to near zero and now your studs are being bent back and forth like a paper clip every time you rotate the wheel. It's only a small amount but eventually you will break the stud and if you are lucky it will happen when tightening or loosening the nut.

ARP studs have a 190,000 minimum psi tensile strength vs. Class 10.9 which is 150,000 psi. which is a 25% improvement. Great, they are better, but do you really need it?

Hope this helps.

So under normal conditions your permissible wheel load could go from 28,800 lb to 36,500 lb. using ARP studs, but what is the point? Your tires are only load rated for 1,500 lb or so. Think about it 28,800 x 4 wheels = 155,200 lb capacity with a 3,200 lb car. 36:1 safety factor with stock studs!

Go to www.arp-bolts.com website for more information.

I stand by my opinion that stock GM studs are good enough for racing.

froggy47

My gut told me that all these folks that grease the contact surface between rim and disk brake and bearing (to prevent them from rusting together) were messing around with the engineering of keeping wheels on the car. Guess the gut was right. I never did/do that. That stays clean & dry.

I also agree that the stock studs are more than sufficient but with different rim center thickness and or spacers (another day for that topic) I like the extra few threads with the arp's that are threaded all the way.

Thanks for the info.

I really don't think either of the guys that had failures had loose nuts, but both were multi year old cars & who knows if something was overtorqued at some point.

I assume that once the first stud fails there is a sort of domino effect on the others.

JiminVirginia

Good description. I had these issues last year with the OEM studs. After years of use (car is a 2004) the threads just started to give way. I replaced them with extended ARPs. Missed two events in the process, but you live and learn.

Jim

Solofast

When this happens it is almost always the result of getting a tiny sliver of aluminum in the threads when removing or replacing the wheel. If you drag the wheel over the studs, it will shave off a tiny sliver of aluminum. If you don't wipe it off the threads, it will get between the nut and the stud and then when you torque the nut it WILL get smashed in the threads, but it will torque up ok. When you try to remove the nut it will turn about one turn before it will gall and the only way to get it off is to break the stud. Some aluminum wheels used to have steel inserts pressed into them (my Mazda's did) to prevent this, and the problems with galling under the lug nuts, but those days are gone and now almost all wheels are just machined aluminum and this is an issue.

Been there, done that. Learned the lesson. When removing wheels, lift the wheel so that you don't drag it across the studs. Then, ALWAYS wipe the threads when you get the wheel off, and when you are reinstalling the wheel be careful to lift it and put it straight on and not to drag it across the studs. Problem solved....

trapp

I was wondering if trying to remove them when the wheels are hot from the track session has anything to do with it? Should you wait until they cool before changing wheels? Just a thought...

bsalie99

Keep in mind that GM lug studs are CRAP. They use the same poorly made lug stud in the vette that is used in the low end cobalt. I have seen more stud failure on GM cars than any other. As said above 99% have been during removal/install. It is not a racing thing, it happens even more in street cars. Not even the new cars are better My wife drives a G8, it had larger thicker studs ( same size as my tahoe, but they dont interchange) they are always torqued to spec. never used an air gun on. one just failed on tightening at about 50 ft/lbs . and it was a 150.00 fix to get replaced, the entire spindle had to be pulled, and it was a drive wheel. I have never seen a ARP lug stud break, unless the car was run on hand tight nuts.

froggy47

froggy47

I would agree that removing them hot is probably not good for the threads. I have never had the need to do that. They do cool off very fast, minutes.