What lug nut torque have you settled on?

[PC_GUARD]

What is not a controversy is that the studs are 14mm
What is not a controversy is that Ford say 150
What is not a controversy is that 14mm requires more torque than 1/2 or 12
What is not a controversy is that Ford know better than the people that want to see a controversy where there is none

AND wheel lugs will effect wear on wheel bearings.

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[Ewheels]

What are the exact specs of the factory studs?
Size: M14 x 1.5
Thread: Coarse or Fine (I believe they are coarse but can't find confirming information)
Grade: also cannot find confirming information but either grade 8 or 10
Lube: again, cannot locate confirming information but I would assume dry

 

[MAGS1]

What is not a controversy is that the studs are 14mm
What is not a controversy is that Ford say 150
What is not a controversy is that 14mm requires more torque than 1/2 or 12
What is not a controversy is that Ford know better than the people that want to see a controversy where there is none

Exactly. “Point of view” means zip. If you’re on the OEM studs, torque to the OEM specs. If your lugs can’t handle it, get different ones. Gorilla and others make them specifically for the S550. If a wheel can’t handle 150 ft/lbs of torque without being compromised, it’s a piece of $hit wheel. There are numerous options out there that can handle it just fine

 

[Egparson202]

If I was running OE hardware, I’d torque to 150 lb-ft.

Since I’m not, I’ll be following the specs provided for the upgraded hardware. Here’s a bit from their product page:

“These are Racing Lug Nuts with a low friction coating and require much less than the factory torque specification to properly pre-load the wheel stud. We recommend reducing the torque value from 150ft/lbs. to 120ft/lbs. Lubricants are not required and strongly discouraged. Threads may be cleaned periodically with a brush and lightly wiped down with a light lubricant such as WD40. If you are using these on very used wheel studs with damaged or worn threads please replace your wheel studs. If these are used with our coated wheel studs the torque value should be reduced to 100ft/lbs and adjustments made in small increments to find the ideal torque value for your vehicle after the vehicle has been run through a track session and allowed to cool. If the wheels are maintaining torque consistently there is not need to apply a higher torque.“

 

[tosha]

What are the exact specs of the factory studs?
Size: M14 x 1.5
Thread: Coarse or Fine (I believe they are coarse but can't find confirming information)
Grade: also cannot find confirming information but either grade 8 or 10
Lube: again, cannot locate confirming information but I would assume dry

Here' the confirming information , these are class 10 bolts

 

[Dana Pants]

So after 5 pages and some hints from @sigintel that the failure was likely fatigue, I decided to put on my engineering hat and chase some numbers.

Chapter 0: The Patient
-The car is a dual-driven autocross device running -4.1 degrees front camber and -2.7 degrees rear camber on 18x11 wheels. Its completed over 800 ~1 mile runs that I've documented, and probably a bunch that I have not. Power is stock and with that much camber the car doesn't put power down or stop well anyways. The car has mid-corner grip for days. The odometer reads 40k miles. 3 of 4 wheel bearings have been replaced due to field failures, the lug stud failed on the only remaining factory wheel bearing. Lugnuts always torqued to 140 ft-lbs.

Example:


Chapter 1: Going Straight
-A M14 bolt has a clamping load of ~60kN
-Chasing that through the lugbolt pattern with a coefficient of friction of 0.6 yields a holding torque of ~10kNm due to friction alone. This assumes everything is dry and uncontaminated.

-The max allowable shear load of a M14 bolt across the threads is ~74kN
-Chasing that through the bolt pattern yields a holding torque of ~20 kNm due to the bolts

-Chasing peak engine torque of 570 Nm through first gear yields ~4.5kNm per wheel

Therefore whether friction or the bolts resolve the toque of the engine and brakes doesn't really matter, as the combined torque holding ability is 6 times higher than what the engine will deliver.

I don't consider brakes critical as this is the rear axle that failed. I didn't assume some shock load for launching because we race on unprepared surfaces that rarely have straight starts although I did kill an axle.

Chapter 2: Turning
If you put half the car weight over one axle, assume the inside tire is completely unloaded, and a cornering acceleration of 1.2g, you end up with an acceleration force of ~9.5kN where the rubber hits the road.

This results in a ~3kNm torque trying to bend the wheel in the direction it doesn't rotate.

If I do statics across the bolt pattern and assume two bolts resolve the load at all times, this is a ~13 kN cyclic tension load on the bolts happening once per rotation.

800 miles of racing and a tire that rotates 800 times per mile = 640k Cycles. Maybe divide that by 3 due to turning left and right as well as the transition between turns and you get 200k cycles.

The endurance limit of steel is typically ~1/2 the ultimate tensile strength and the ultimate tensile strength of a M14 grade 10.9 fine thread bolt is 130 kN.

130kN/2 = 65 kN.

If you take a 60 kN pre-tension and cycle it with 13 kN, it is not unreasonable that the wheel stud fatigued as the paper study puts us right into the danger zone.

Worth noting is that the loads due to turning have much lower factors of safety than the loads due to going straight, further highlighting that this is the critical direction.

Based on this non peer-reviewed and somewhat rushed engineering analysis and literature review I have the following conclusions:

Literally every fastener publication ever says the best way to avoid bolt fatigue is to tighten fasteners to the recommended level. -> OK, I wont try to outsmart the world by lowering my toque specs.

Clean the mating surfaces and threads with carb cleaner -> OK

Wheel studs are a wear item in motorsports -> Deal with it.

Afterthought:
Wheel studs don't have to last forever, they just have to last longer than the wheel bearings.

 

[sigintel]

If I was running OE hardware, I’d torque to 150 lb-ft.

Since I’m not, I’ll be following the specs provided for the upgraded hardware. Here’s a bit from their product page:

“These are Racing Lug Nuts with a low friction coating and require much less than the factory torque specification to properly pre-load the wheel stud. We recommend reducing the torque value from 150ft/lbs. to 120ft/lbs. Lubricants are not required and strongly discouraged. Threads may be cleaned periodically with a brush and lightly wiped down with a light lubricant such as WD40. If you are using these on very used wheel studs with damaged or worn threads please replace your wheel studs. If these are used with our coated wheel studs the torque value should be reduced to 100ft/lbs and adjustments made in small increments to find the ideal torque value for your vehicle after the vehicle has been run through a track session and allowed to cool. If the wheels are maintaining torque consistently there is not need to apply a higher torque.“

That info would only apply to something like non zinc or non chromate plated finish and likely a LCP or Fluro coating on a porous plating (phosphate black etc).
Aircraft or actual NASCAR hardware?
Seems overkill unless you are endurance racing and need fast tire changes....

 

[sigintel]

-The max allowable shear load of a M14 bolt across the threads is ~74kN
-Chasing that through the bolt pattern yields a holding torque of ~20 kNm due to the bolts

The allowable shear load on the lug bolts in service is 0.
100% of the shear load is to be handled by the friction of clamping.

Any under torque is risking the assembly parts moving in relation to each other cyclically and putting the studs in bending and shear.

If you under torque, your wheel and hub become a metal shear....

 

[tosha]

That info would only apply to something like non zinc or non chromate plated finish and likely a LCP or Fluro coating on a porous plating (phosphate black etc).
Aircraft or actual NASCAR hardware?
Seems overkill unless you are endurance racing and need fast tire changes....

That's what Time at OPMustang sells and typicall usecase is for really wide wheels that require more than 25mm spacer - definitely not something one would need on a street.

 

[sigintel]

That's what Time at OPMustang sells and typicall usecase is for really wide wheels that require more than 25mm spacer - definitely not something one would need on a street.

Two different issues:
1. The durability of the stud and lug threads.
2. length of bolt needed to clamp a thicker assembly.

OPMustang looks to be selling actual race grade hardware:
Finish plating looks like Phosphate Oxide or Manganese Phosphate or Zinc Phosphate.
Solid film coating (Dry film) could be MoS Sandstrom, Everlube, Molycote 321, CT-xx, etc.
These are aircraft/milspec/racespec fixture systems and those providing the system better have a damn good understanding of initial, mature, EOL and contaminated performance to provide both a service procedure and initial spec for torque.
....which it looks like they did.

These coatings increase durability by decreasing wear via lower friction. This lower friction allows achieving the same preload (clamping force) with less torque. The bolt is still providing pure tension clamping force.

The coating addresses durability.

Length of studs addresses thicker assembly due to large spacers.

 

[Rapid Red]

Personally, I don't question torque values on anything, use what the manufacturer recommends.

 

[tosha]

Two different issues:
1. The durability of the stud and lug threads.
2. length of bolt needed to clamp a thicker assembly

Absolutely. The reason I mentioned length is to point out that this is track/race grade product that people use for that specific usecase, and OPMustang seems to be catering to this crowd very well so far with great products.

That wasn't intended to be advertisement though

 

[Egparson202]

Absolutely. The reason I mentioned length is to point out that this is track/race grade product that people use for that specific usecase, and OPMustang seems to be catering to this crowd very well so far with great products.

That wasn't intended to be advertisement though

They *are* nice parts. I’m using the car primarily for track days. And as someone noted earlier, there’s no room for failures at speed.

 

[TrackMustang]

What is not a controversy is that the studs are 14mm
What is not a controversy is that Ford say 150
What is not a controversy is that 14mm requires more torque than 1/2 or 12
What is not a controversy is that Ford know better than the people that want to see a controversy where there is none

What is not controversy issue that you’re annoying
What is not controversy is that I don’t care about your opinion
What is not controversy is that this is exactly why forums that should be an interesting way to exchange ideas and information about cars people are passionate about, but instead they’re filled with assholes.

5 pages of comments on the subject in a couple days but you’re right, there’s only one correct answer

 

[Egparson202]

5 pages of comments on the subject in a couple days but you’re right, there’s only one correct answer

I think there’s a correct answer for OE and that’s all some people are taking into consideration. Fine.

Then there’s other hardware, and other members who need to search a little deeper. Asking the same questions of a more track-focused audience might yield a more balanced discussion.

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