so all us track guys know using studs is widely accepted, but they are a wear item!, and stories exist where there were catastrophic fails,..right?...and many believe bolts are waaaay safer.
so yesterday at Lime Rock an instructor goes off..........ALL 5 BOLTS sheared......
turns out he runs wheel spacers and had instlld longer bolts, but he didnt recall where he sourced them from.
Another instrctr( also a mech eng) looked at sheared bolts sticking out of hub and it was clear to him they appeared below grade. I didnt ask what he noticed. Car had body damage, susp damage brake damage.$$$$$$$
soooo........pls use only good hi grade stuff........it can get scary out there.
MZ3 coupe.....nice car.
Last edited by jrkoupe; 04-15-2018 at 02:03 PM.
Even if you use good quality parts, change them out every year as routine maintenence. Probably one of the cheapest components on the car, but as you point out if they fail ......
I dunno if I can be 100% onboard with this rec.
Yeah better safe than sorry is a good mantra,,, but I change studs "preventively" when I change wheel bearings preventively which is about every 5-6 seasons and I know I am throwing away perfectly good studs (and wheel bearings for that matter).
I can only say from my experience I have never broken a stud or had one fail since I installed my first set in 1998.
Now newer bigger, heavier, more powerful cars may change the game, I race a 2200 lb E30M3 but I am on slicks and its not driven timidly.
I think every year is excessive unless there is data out there to back that up of failures occurring after one year of use.
jimmy p.
88 E30 M3 Zinnoberot - street
88 E30 M3 Lachsilber - SCCA SPU
87 E30 M3 Prodrive British Touring Car 2.0 Litre
04 Ford F350 - V10
06 Audi A3 Brilliant Red / 2.0 / DSG
That's why I'll only ever buy studs from GLS (I'd buy from ARP too if they made something for us). They're the only ones who will tell me where they're made and how/from what. There are a pile of "motorsport" things out there who make claims about their products but when you ask them for proof of certification and the manufacturing facility, you get crickets or that it's secret bro.
GLS?........never heard
http://glstopstud.com/
Their web store:
http://www.trackstuds.com/
very awesome....
I just broke ONE. Cause, I set my torque wrench in the dark. On inspection found 2 others that were ever so slightly bent. They were 3 years old. So, replaced them all with BW race bullet nose;
http://www.bimmerworld.com/Wheels-Ti...Stud-82MM.html
They sure do look extremely similar to the GLS studs.
After four years, i just swapped in a set of the standard Bimmerworld studs. Race were kinda pricey.
Yea, they're probably overkill. But I liked the sizes they came in. I also mixed and matched and put longer ones in front.
Thinking about it, there's the engineering/metalurgy question that asks if higher tensile strength is actually better in this application?
In the absence of a real engineer, in my opinion, yes. Yield strength specifically. The wheel fastener's primary role is to clamp the wheel to the hub, they should not be shear load bearing structures (granted, shear strength will go up with tensile too). Which is why GLS makes theirs out of 4340, chromoly that gun barrels are made out of. It doesn't mean you need to make use of the added clamping force capacity but it will just have an easier time with the application being so far below the limits.
I agree with the tensile strength being important for cornering, but wouldn't the shear strength be important for braking/accelerating?
As I understand it, with the hub/wheel joint under proper tension, the fasteners should not be under shear load. But again, shear strength goes up with tensile so if for some reason your wheel is loose and moves, the higher tensile strength fastener will add a measure of safety there too.
I was just thinking that a higher tensil metal ?may? be less flexible, or less resistant to heat cycles? Don't know, just spitballing. Anyway, I bought the fancier ones mostly because I could get the exact lengths I wanted.
I can't think of a downside personally (other than cost). They will certainly be less flexible which is also a good thing, as they will be less likely to fatigue out. And chromoly is sensitive to heat but not at this level (you'd have to heat them up to the transitional temp). GLS also rolls their threads instead of cutting so they are much stronger.
Could easily be mis-handling of re-torquing procedures on hot studs or lack of re-torque after initial heat cycling. Seems like this is just as important as the blingy-ness of your wheel studs/bolts.
Very happy with my GLS studs, ~3 years thus far, r-compounds only
While the tensile strength is important, the most important point is using the proper torque spec. The idea of torquing the fasteners is to be in the elastic range of the fastener. This will slightly stretch the stud, but in the elastic range it will always return to its original dimension and properties.
When you torque the bolt past the elastic range and reach plastic deformation, the bolt will neck, usually at its thinnest point (point of highest specific stress) also lengthening the bolt. This will result in strain hardening of the bolt in the regions of plastic deformation. The bolt may be harder in this region, but its ductility is also reduced. Future applications of load will now also experience higher specific stresses in the necked area.
I have heard nonsense arguments that the brakes can heat the fasteners enough to soften them, but this is not the case. The eutectoid temperature is 727°C (transformation) for carbon steels, so your studs on a Z3M are not going through recrystallization.
Make sure that you find & abide by the torque spec for your studs. I use the Italian ones from BW, and on contacting them they have told me to use 75ft-lbs. I have the same studs for over 10 years and too many events & wheel changes to count. When torquing, stop application of force once the ratchet clicks. I see a lot of people misuse torque wrenches by clicking & then giving an extra oomph. If you want to check, release the wrench & only reapply enough force to click.
Finally, wheel studs are not the only fasteners to torque properly. BMW has assigned specs to most fasteners, and following these is important to the longevity of the parts & fasteners and overall reliability of the vehicle. It really takes very little extra effort to properly torque fasteners.
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^ Great post. Usable info!!
I've been torquing to 100Nm (=74ft-lb), so this makes me feel good.:
There should be no shear load on the fasteners on a properly installed wheel. The studs will be under a tensile load. There is a fictional interface at the hubs which translates the forces from the wheel into the suspension.
This is why you should make sure that the wheels are tightened to the hub before lowering the car onto the wheels.
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This is why you should make sure that the wheels are tightened to the hub before lowering the car onto the wheels.
bingo
Noticed the lug nuts were getting a little shoddy when swapping tires at NCM last weekend along with some more advanced front rotor cracks. Opted to order the Bimmerworld Premium Race (12.9 grade steel) stud & lug nut kit and new front rotors.
http://www.bimmerworld.com/BimmerWor...d-Package.html
Had the street version (10.9 quality steel) on the M3. I'm not sure how old they were so it seemed like prudent preventive maintenance.
Feff
Keep in mind that harder is not always better. A harder bolt will necessarily have a higher torque spec to get into the elastic range, and this may be more than the bolt threads or mating surfaces can handle.
A 12.9 has an ultimate tensile strength about 20% higher than a 10.9, so I'd guess that you won't deform or gutter out good aluminum wheels, but I would check.
Also note that 12.9 might be a more exotic alloy than the carbon steel 10.9s, so make sure that the alloys are designed for the application to prevent corrosion-induced failure.
BW is a good company, so just reach out to them to verify proper installation.
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Why do you need to torque it to yield just because it has higher yield strength? Keep the same clamping force, just have more overhead if things don't go right (such as a bad torque wrench or a gun-happy tire installer)
Sorry I wasn't clear, and I hijacked a little to cover all fasteners.
You don't want to yield the bolt, but you do want strain (deform) in the elastic region. The reason for the higher torque spec on harder fasteners of a given dimension (M12 10.9 or 12.9, for instance) is due to the stretch that you want in the bolt. Clamping force between the parts is one aspect, but the orthogonal force between the threads, which is what keeps the bolt from backing out, is equally important.
Again, I'm not saying that it won't work. I just wanted to point out that:
1 Higher strength is not always better for a given application
2 Contact the seller and make sure that you understand if there are changes into the torque spec.
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