Just to verify that I'm reading the manual correctly.... are the lug nuts on the 350R carbon fiber wheels supposed to be torqued to 150 ft lbs? Taking car to track tomorrow. Believe the dealer only torqued them down to 100 ft lbs... after checking one.
Lug nut torque?
- Thread starter Mwynn
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Correct
I'd be much more concerned about the torsional capacity of the studs. The longitudinal tension capacity of a steel bar the diameter of the studs is quite large (i.e. how much load is pulling on the threads to pull the stud outward) but when tightening, 150 ft-lbs is terrifying because doing it "dry" runs the risk that the threads bite a little too much before it's seated (and friction of the seat to add to the torque resistance) and "snap" there goes a lug.
I personally am not tightening to more than 130 unless I go to the track with it. On the street, there's absolutely no reason to torque them that much and for as many times as I yank the wheels on or off, it's not worth the risk of snapping a stud. If I go to the track to beat on it and the wheels feature their max loads, I'll torque them down to spec.
I personally am not tightening to more than 130 unless I go to the track with it. On the street, there's absolutely no reason to torque them that much and for as many times as I yank the wheels on or off, it's not worth the risk of snapping a stud. If I go to the track to beat on it and the wheels feature their max loads, I'll torque them down to spec.
The torque spec from Ford is actually 135lb-ft to 165lb-ft.
Page 41 of the GT350 Owner's Manual Supplement.
http://www.fordservicecontent.com/F...350-Supplement-version-1_su_EN-US_04_2016.pdf
Unless you know you have perfectly rolled and clean nut and stud threads, I'd err on the low side of the spec.
Page 41 of the GT350 Owner's Manual Supplement.
http://www.fordservicecontent.com/F...350-Supplement-version-1_su_EN-US_04_2016.pdf
Unless you know you have perfectly rolled and clean nut and stud threads, I'd err on the low side of the spec.
The +\- on torque values are there for error on your torque wrench’s calibration. I would suggest 150 just like the people who built the vehicle suggest
Ditto. I always torque mine to the 150 ft-lbs recommendation. OP, just make sure you don't have any rust on the studs, and you'll be fine. If you have rust, clean it off with a metal wire brush (the toothbrush from hell) before you put the nuts back on.
Fastener manufacturers know that the typical torque wrench is not always calibrated to perfection at a given moment or at all times. Regardless, the number they provide is as close to the median figure that imparts the most precise amount of stretch they are looking for. That said, the +/- figures are within the range of their engineered parameters when using calibrated testing equipment. As such, if you have a good wrench you are hitting that range whether on the low or high side.
This is one area where Ford Engineers dropped the ball. The reasons for not overtorquing are numerous, but the biggest being warped rotors and sheering off lugs. Ford eliminated the first concern with the 2 piece rotors, but if the loads were such that they're concerned about material deflection and vibrations, they should have gone with a 6 lug configuration or even more.
Even hitting a tractor trailer with an air gun hard probably doesn't equate to 150 ft-lbs torque wrech and instead of asking for some ridiculous torque load on 5 lugs, they increase the amount of lugs accordingly. I get that weight is always a concern, but they didn't seem too concerned about wheel weight/rotational mass when putting 33 lb wheels on the regular 350 (outward where it hurts way more than at the central hub). They should have just gone with more lugs. This isn't NASCAR or Le Mans where you're worried about Pit times either.
Even hitting a tractor trailer with an air gun hard probably doesn't equate to 150 ft-lbs torque wrech and instead of asking for some ridiculous torque load on 5 lugs, they increase the amount of lugs accordingly. I get that weight is always a concern, but they didn't seem too concerned about wheel weight/rotational mass when putting 33 lb wheels on the regular 350 (outward where it hurts way more than at the central hub). They should have just gone with more lugs. This isn't NASCAR or Le Mans where you're worried about Pit times either.
I think a lot of you are confusing torque with tight. The S550 has very large studs. Those studs have more surface area and thus create more friction. 150lb on these studs would be about the same "Tightness" as 100lbs on a 12mm stud with the same thread pitch. It is all about how tight something is. And this is why, with more lugs, you need less torque. You can create the same amount of clamping force with less torque per lug,. by increasing the amount of lugs. Torque to yield nuts/bolts is a bit of both. It is about getting things tight and applying enough torque to create stretch in the fastener.
ANGREY said:
The OEM's do not cut corners with respect to strength when it comes to junctures such as a wheel/hub interface. The increase to an M14 stud over the previous 1/2" units brought with it an increased torque figure to impart the proper amount of stretch. That said, all of them understand there will be failures at a calculated sampling number. There is always the potential for manufacturing inconsistencies as well.
In order to minimize or mitigate the opportunity for failure you should always take heed in the manufacturer's specifications, ensure that the threads on both the nut and stud are clean and damage free, and torque by hand. Avoid using an impact gun/socket here.
If you search on Google long enough, you'll eventually find tables of clamping force vs. torque for metric and inch fasteners. Having done that exercise, it turns out that an M14x1.5 stud tightened to 150 ft-lbs clamps the rim to the hub with roughly (+/-10%) the same clamping force (about 18,000 pounds per stud) that a 1/2" fine-threaded stud does when it's tightened to 100 ft-lbs.
The higher torque on the larger stud doesn't hold the wheel on any tighter, but the bigger stud is 40% stronger. That's worth having.
What's not accounted for is that the total force to remove the wheel depends on the number of studs. Imagine if engineers just said "well Billy, we can't use more than 4 studs to design this tractor trailer wheel, so we're just gonna have to go with bigger studs and/or crazy torque on them."
There's a reason that super duty trucks and large vehicles use MORE studs, even when the wheels aren't that much larger. More studs = more total retention force.
I'm wondering if the torque is more for vibrational concerns, if the "clamping" force is comparable to smaller fine thread studs with less torque applied.
Either way, I don't care if the studs are bigger, it makes me pucker trying to torque them anywhere close to spec because (raise your hand if you've ever snapped off a stud) it's not exactly a quick/easy process to remedy. ESPECIALLY if you happen to be somewhere/some time that's inconvenient.
Paraphrasing your post: "well Billy, we can't use more than 1 stud to design this Porsche wheel, so we're just gonna have to go with a really big stud and crazy torque"
Billy's response was "no problem - let's use a single stud that's 2.36" diameter right in the middle of the wheel and tighten the nut to 440 ft-lbs - we could call it a "center lock" wheel"
Billy's response was "no problem - let's use a single stud that's 2.36" diameter right in the middle of the wheel and tighten the nut to 440 ft-lbs - we could call it a "center lock" wheel"
I'd prefer the Halibrand pin-drive style hubs over those PIA Porsche units.
I'd also suggest aftermarket studs to anyone that is constantly swapping wheels and tires on their Mustang that is looking for the best in available hardware. MSI and ARP make some great stuff that is as strong as it gets. I just did the front and rear of my Fox build with some ARP's from Maximum Motorsports - consider me impressed with the quality.
I'd also suggest aftermarket studs to anyone that is constantly swapping wheels and tires on their Mustang that is looking for the best in available hardware. MSI and ARP make some great stuff that is as strong as it gets. I just did the front and rear of my Fox build with some ARP's from Maximum Motorsports - consider me impressed with the quality.
A friend of mine in the sixties and seventies had a 1963 Jag E-Type with Whitworth spline hubs and knockoffs. He bought the car new and loved it dearly - it was his DD. But, he never stopped complaining about the way that the splined hubs wore. Every decade he needed new rims because the wheels would start wobbling. And new rims weren't perfect either - they always needed the spokes tightened and tuned so they were round enough to give a decent ride with the tube-type Pirelli's he used. Those were the days.
Jump over to the Porsche forums and see how many guys there are running conversion kits to a 4 stud arrangement and report back to us. Center lock wheels brief well on paper and are great if you're running a race team where you do constant high level maintenance to a race car, not so much for wear and abuse for people who don't want to constantly swap out parts. The torsional and isometric forces exerted on wheels lends itself to an attachment method with multiple points for cross sectional stability. It also doesn't place all your eggs in one basket. Center locks wheels are there for all out race teams who also want the rapid swap out because they're interested in shaving down seconds in each pit over many pits in a race.
At any rate, the specs are what they are. It's just a lot of torque for such a small cross section of steel.
I hear you about the Porsche center locks - I've seen them up close on race cars and when the car's equipped with air jacks, a tire change doesn't take long. In the paddock you have a four-foot long torque wrench to tighten them with, but in the pits there's no time for that so you need a calibrated air wrench to make sure you get enough torque to keep the wheel on. They do have an interesting safety feature though - presumably because there's no redundancy with a single 60mm stud, the stud has spring-loaded fingers inside it that extend out when the wrench socket is pulled away. They keep the nut from coming off if it gets loose. You can't do that with regular lugs.
As for the 150 vs 100 ft-lb discussion, I thought you'd raised an interesting issue, so I did some research and found that because of the differences in diameter and thread pitch, it takes 150 ft-lbs on an M14x1.5 to get the same clamping force as you get with a 1/2-20 stud at 100 ft-lbs. It sounds like it's a lot higher but as far as the wheels and studs are concerned, it's the same.
What concerns me about 150 ft-lbs is not the stud, it's the nut. This is not the time or the place for cheap aftermarket lug nuts. For the track, I use OEM Chevrolet open-end lug nuts or OEM Ford closed-end nuts that are rated by the manufacturer for 150 ft-lbs.
As for the 150 vs 100 ft-lb discussion, I thought you'd raised an interesting issue, so I did some research and found that because of the differences in diameter and thread pitch, it takes 150 ft-lbs on an M14x1.5 to get the same clamping force as you get with a 1/2-20 stud at 100 ft-lbs. It sounds like it's a lot higher but as far as the wheels and studs are concerned, it's the same.
What concerns me about 150 ft-lbs is not the stud, it's the nut. This is not the time or the place for cheap aftermarket lug nuts. For the track, I use OEM Chevrolet open-end lug nuts or OEM Ford closed-end nuts that are rated by the manufacturer for 150 ft-lbs.
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