Keep breaking lugs - advice for hardened lugs??

[Quisp]

You're points would be valid if there were 5 or even 100 samples. Were talking 10's of thousands. So get stronger studs and delay another breakage for another thousands of cycles. No fastner will withstand shearing loads or cyclic vibration . Cure the problem, not the symptoms .

 

[maestromaestro]

You're points would be valid if there were 5 or even 100 samples. Were talking 10's of thousands. So get stronger studs and delay another breakage for another thousands of cycles. No fastner will withstand shearing loads or cyclic vibration . Cure the problem, not the symptoms .

My arguments are valid because I know what I am talking about. There are vibrations and stress in any car - but, because they are associated with relatively low stresses, most studs don't crack. See my earlier explanations about fatigue limit.

As to your (not you're) "advice" to "cure the problem" - thanks, Captain. If you read my posts, you'd have realized that I had already ordered better rings. However, I am a fan of belt and suspenders approach.


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[ericr]

Here's an interesting article that might shed light on your problem. I thought the explanation of reverse bending fatigue and loss of clamping force to be of interest.

http://www.meaforensic.com/wheel-se...metallurgical-expert-mark-bailey-mea-forensic

 

[maestromaestro]

Here's an interesting article that might shed light on your problem. I thought the explanation of reverse bending fatigue and loss of clamping force to be of interest.

http://www.meaforensic.com/wheel-se...metallurgical-expert-mark-bailey-mea-forensic

Ultimately, this is all about stress cycles - so, yeah, fatigue. Considering that the root cause of the stud failures takes us to the shallow depths of materials performance (mechanical behavior), here's a simple write up on the subject matter -
http://www.epi-eng.com/mechanical_engineering_basics/fatigue_in_metals.htm

 

[Sekred]

Bolt failure, cyclic reverse bending overload. This is a flywheel bolt, loss of clamping force caused the failure.

 

[maestromaestro]

The fatigue situations are common when there are vibrations, especially when high-frequency ones. To that end, if the part is secured by multiple fasteners, once one of them fails, it increases stresses on the adjacent ones and the whole thing snowballs. Hence the admonishment to check torque frequently; if anything, it would reveal the impacted studs/bolts. The torque for the FiST is high (e.g., a 911 requirement is 'only' 80 lb-ft) - so, a weakened stud will twist off (just like the one on my car).

In the picture above, you can see how the crack initiated and grew inwards and finally the bolt overloaded (ductile failure, the "lip" is visible at the 2 o'clock position). Discoloration shows that this took a bit of time to develop - maybe corrosion, maybe oxidation.

 

[ericr]

I'd be curious to see if you still had these failures if you went back to the factory wheels. I know you've investigated this thoroughly and are convinced of a solution, but it sure sounds like you have a clamping failure leading to shear loads on the studs. Properly clamped, you should not be seeing shear loads. You wouldn't perhaps be spraying corrosion spray on the hub face?

 

[maestromaestro]

I'd be curious to see if you still had these failure if you went back to the factory wheels. I know you've investigated this thoroughly and are convinced of a solution, but it sure sounds like you have a clamping failure leading to shear loads on the studs. Properly clamped, you should not be seeing shear loads.

Ultimately, even with a high torque, the clamping force does not provide enough "mating" to avoid the added bending momentum - hence, the need for the wheel to sit securely on the hub, without any play, so that the studs do not bear additional load. So, you are correct in saying that this is insufficient clamping force - for the specific "geometry" of the current set up, even though the lug nuts are proper for the aftermarket wheels So, you are also correct that this is unlikely to happen with the stock wheels. I suspect that Ford also designed it so that even when the torque is less than the spec (after all, these are the same studs used on all Fiestas, and most owners NEVER check the torque) - the studs would perform. I guarantee that they have run oodles of S-N curves and simulations to determine what would happen if someone only torqued the wheels when the tires are replaced.

 

[Sekred]

Bolt torque is dictated by tensile strength (grade).
I think you touch on it before when you mentioned Root cause. What is the Root cause in this failure analysis?. Fix the root cause. There are plenty of guys running different rim/tyre combinations as well as wheel torque/horse power of plus 300.

 

[maestromaestro]

Bolt torque is dictated by tensile strength (grade).
I think you touch on it before when you mentioned Root cause. What is the Root cause in this failure analysis?. Fix the root cause. There are plenty of guys running different rim/tyre combinations as well as wheel torque/horse power of plus 300.

Dude, I hear you. The root cause is vibration because of the shitty hub centric rings. No mystery. Ordered and installed. We'll see - but, in the meantime, I'd be interested in stronger studs so that I would have suspenders to the belt. I appreciate the desire to help, but - already addressed in the earlier posts.

 

[Sekred]

Cool, let us know if you get it sorted.

 

[Kazz]

Ignorance and confusion alert: who's hub centric rings are flawed/cheap/dangerous and what is the actual torque listed for lug nuts on the FiST? I'm used to 68-80 lb ft. Thanks.

 

[awwwww_shift]

Ignorance and confusion alert: who's hub centric rings are flawed/cheap/dangerous and what is the actual torque listed for lug nuts on the FiST? I'm used to 68-80 lb ft. Thanks.

Owners manual and service manuals both list wheel lug torque of 100 ft/lb...

http://www.fordservicecontent.com/F...-ST-Supplement-version-1_st_EN-US_05_2015.pdf

(page 25)

 

[Kazz]

Owners manual and service manuals both list wheel lug torque of 100 ft/lb...

http://www.fordservicecontent.com/F...-ST-Supplement-version-1_st_EN-US_05_2015.pdf

(page 25)

That is just plain nuts - no pun intended.

 

[maestromaestro]

That is just plain nuts - no pun intended.

That or risk the stud failures. Loose nuts in conjunction with non-hub-centric wheel is a double whammy.

 

[Zormecteon]

That is just plain nuts - no pun intended.

I thought it high too, but it's their stuff... the red thing (see avatar) "book" is 40 ft/lbs.... That seems awfully low, but then the studs are only 3/8".

When I tell them at the tire shop to use a torque wrench set to 40 ft/lbs they look at me like they want me to sign a waiver. LOL

 

[M-Sport fan]

I thought it high too, but it's their stuff... the red thing (see avatar) "book" is 40 ft/lbs.... That seems awfully low, but then the studs are only 3/8".

When I tell them at the tire shop to use a torque wrench set to 40 ft/lbs they look at me like they want me to sign a waiver. LOL

My 4th gen LS1 f body was also 100 lb. ft., but it WAS the same exact factory stud size as the FiST, just 5 of 'em per wheel instead of 4.

 

[D-resonant]

Are you running 4x100 converted hubs?

 

[maestromaestro]

Are you running 4x100 converted hubs?

I am assuming you're asking me? The answer is yes. Why?

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[D-resonant]

I am assuming you're asking me? The answer is yes. Why?

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Curious if a slightly miss-drilled/aligned 4x100 pattern be part of the problem.