I thought this might make for an interesting discussion topic, but reading another thread indicated that the 14 mm wheel studs on the 2015 up S550 "requires" 150 lb ft of torque. Interestingly enough, that is the same stud size and torque spec for my F-150. Now I'm not an engineer, but I've taken more than a few engineering courses in college while figuring out my future career, so in my mind I think it's overkill, so I'm going to argue against said requirement.
First off let's start with every generation of mustang prior to 2015. They all came with 1/2-20 wheel studs and lug nuts. Torque specs range between 80 to 105 lb ft. Bolts come in varying grades and has to do with the strength of the bolt and how much clamping force it can exert. SAE has a different grading system than metric, but the higher the grade, the stronger the bolt. For each size and grade there is a maximum torque specification. Even that is skewed by whether the bolt is coated or lubricated. I'm sure specs vary slightly depending on the source, but the variance should be minute. The source I'm using comes from Fastenal's website.
For a 14 mm bolt with a 10.9 classification (grade) shows a maximum dry torque spec of 148 lb ft. The lubricated spec is 111 lb ft. Both would yield a clamp load of 16,154 lbs. If we drop down a grade class to 8.8 for 14 mm bolt, the torque spec dry and lubed is 104 and 78 lb ft, respectively. The clamp load at that spec is 11,289 lbs.
Looking at the old standard, the 1/2-20 in grade 8 has a maximum torque spec for dry and lubed at 120 lb ft and 90 lb ft, respectively. Dropping down to grade 5, we see specs for dry and lubed at 85 and 64 lb ft respectively. The clamping force for grade 5 and grade 8 are 10,197 lbs and 14,396 lbs, respectively. I'm not sure why the maximum torque spec for the mustang doesn't go to 120 lb ft, unless the stud is not quite up to grade 8 standards. The point being the max torque spec is probably yielding a 12,000 lb clamping load, give or take.
Granted I don't use a torque wrench to tighten my wheels, but I don't use an impact either. I've taken the wheels off my truck quite a few times and I seriously doubt I'm tightening these nuts much more than 100 lb ft. When I've removed them they're always tight. I guess one of these days I'll get out the torque wrench and figure out how tight I'm going.
It just seems to me Ford is using a torque spec that is in the maximum safe range for the fastener and that a 14 mm stud (.55") might be a little overkill in a 4,000 lb car. They are using a 6th stud in the truck line too. That's not to say I would recommend something less than 150 lb ft of torque if I tracked the car.
If someone has different insight, I'd like to hear it.
First off let's start with every generation of mustang prior to 2015. They all came with 1/2-20 wheel studs and lug nuts. Torque specs range between 80 to 105 lb ft. Bolts come in varying grades and has to do with the strength of the bolt and how much clamping force it can exert. SAE has a different grading system than metric, but the higher the grade, the stronger the bolt. For each size and grade there is a maximum torque specification. Even that is skewed by whether the bolt is coated or lubricated. I'm sure specs vary slightly depending on the source, but the variance should be minute. The source I'm using comes from Fastenal's website.
For a 14 mm bolt with a 10.9 classification (grade) shows a maximum dry torque spec of 148 lb ft. The lubricated spec is 111 lb ft. Both would yield a clamp load of 16,154 lbs. If we drop down a grade class to 8.8 for 14 mm bolt, the torque spec dry and lubed is 104 and 78 lb ft, respectively. The clamp load at that spec is 11,289 lbs.
Looking at the old standard, the 1/2-20 in grade 8 has a maximum torque spec for dry and lubed at 120 lb ft and 90 lb ft, respectively. Dropping down to grade 5, we see specs for dry and lubed at 85 and 64 lb ft respectively. The clamping force for grade 5 and grade 8 are 10,197 lbs and 14,396 lbs, respectively. I'm not sure why the maximum torque spec for the mustang doesn't go to 120 lb ft, unless the stud is not quite up to grade 8 standards. The point being the max torque spec is probably yielding a 12,000 lb clamping load, give or take.
Granted I don't use a torque wrench to tighten my wheels, but I don't use an impact either. I've taken the wheels off my truck quite a few times and I seriously doubt I'm tightening these nuts much more than 100 lb ft. When I've removed them they're always tight. I guess one of these days I'll get out the torque wrench and figure out how tight I'm going.
It just seems to me Ford is using a torque spec that is in the maximum safe range for the fastener and that a 14 mm stud (.55") might be a little overkill in a 4,000 lb car. They are using a 6th stud in the truck line too. That's not to say I would recommend something less than 150 lb ft of torque if I tracked the car.
If someone has different insight, I'd like to hear it.
