• Sign Up! To view all forums and unlock additional cool features

    Welcome to the #1 Fiesta ST Forum and Fiesta ST community dedicated to Fiesta ST owners and enthusiasts. Register for an account, it's free and it's easy, so don't hesitate to join the Fiesta ST Forum today!


Keep breaking lugs - advice for hardened lugs??

Quisp

1000 Post Club
Messages
1,118
Likes
402
Location
Davenport
#41
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 .
 


OP
maestromaestro

maestromaestro

1000 Post Club
Messages
1,008
Likes
381
Location
Houston
Thread Starter #42
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.


Sent from my Pixel XL using Tapatalk
 


Last edited:
OP
maestromaestro

maestromaestro

1000 Post Club
Messages
1,008
Likes
381
Location
Houston
Thread Starter #44
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

1000 Post Club
Messages
1,395
Likes
401
Location
Mid North Coast
#45
Bolt failure, cyclic reverse bending overload. This is a flywheel bolt, loss of clamping force caused the failure.

IMG_2539.JPG
 


OP
maestromaestro

maestromaestro

1000 Post Club
Messages
1,008
Likes
381
Location
Houston
Thread Starter #46
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.
 


Messages
151
Likes
67
Location
Sammamish
#47
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?
 


OP
maestromaestro

maestromaestro

1000 Post Club
Messages
1,008
Likes
381
Location
Houston
Thread Starter #48
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

1000 Post Club
Messages
1,395
Likes
401
Location
Mid North Coast
#49
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.
 


OP
maestromaestro

maestromaestro

1000 Post Club
Messages
1,008
Likes
381
Location
Houston
Thread Starter #50
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.
 


Messages
312
Likes
40
Location
Peoria
#52
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.
 


Messages
244
Likes
51
Location
Milwaukee
#53
Last edited:

Zormecteon

Active member
Messages
567
Likes
361
Location
Kelso
#56
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

9000 Post Club
Messages
13,996
Likes
6,697
Location
Princeton, N.J.
#57
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. ;)
 




Top