kvom
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When a wheel is mounted on a car or truck, is the vertical weight carried mainly by the clamping force on the wheel mount surface, or conversely by the studs themselves?
Wheel mount question
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Schrodingers Cat
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some vehicles have a centerbore that carries some load...
but the studs are under tension and shear
but the studs are under tension and shear
M Fan
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Hub-centric wheels which are generally OEM and more expensive aftermarket wheels have the center bore machined for the specific car. This allows the wheel's center bore to support most of the weight and force and then the lugs mainly secure the wheel on the hub.
Many aftermarket wheels, to reduce costs, have gone with an over-sized center bore and plastic or aluminum centering rings that are made to the spec of the car's hub. These hub designs still support some of the weight and the lugs again are used mainly to secure the wheel on the hub as well as support the weight.
Ultra cheap aftermarket wheels use an over-sized center bore and rely on the lug nuts or bolts to not only secure the wheel to the hub, but also support the weight as well.
Many aftermarket wheels, to reduce costs, have gone with an over-sized center bore and plastic or aluminum centering rings that are made to the spec of the car's hub. These hub designs still support some of the weight and the lugs again are used mainly to secure the wheel on the hub as well as support the weight.
Ultra cheap aftermarket wheels use an over-sized center bore and rely on the lug nuts or bolts to not only secure the wheel to the hub, but also support the weight as well.
pseudorealityx
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The studs do not take a sheer force. If they do, they will fail quickly. Studs are NEVER meant to take sheer loads.
The studs are in tension, and that clamping force is what carries all sheer loads.
-mechanical engineer by trade
The studs are in tension, and that clamping force is what carries all sheer loads.
-mechanical engineer by trade
pseudorealityx
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hub centric vs. lug centric wheels only deal with centering. The studs/lug bolts NEVER hold sheer force. They do not support the weight.
Agreed but hub piloted wheels do provide an extra layer of support.
Clamp load generated by torque on wheel studs then creates friction that holds wheel to hub.
This is the case for the majority of all bolted connections- you do not design for most fasteners to be in shear - you design for clamp loads to hold parts in place. I have been doing some testing lately at work and to get a feel for the clamp loads from one fastener- a 16mm (about 5/8") bolt torqued to ~140 ft-lb generally has a clamp load somewhere around 25,000 lbs.
A 6mm or 1/4" fastener at 120in-lbs is about 3000 lbs of clamp force
pseudorealityx
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Not really. If the clamping force were to not be there, all of your drivetrain torque would go through the studs. There's your failure mode. Not to mention as you turn, and the wheel gets laterally loaded up.
Hubcentric wheels aren't really that important with any wheel that uses tapered lugs. Its things like 90's Toyotas, that used lug nuts with sleeves on them, and no taper that hubcentric can become important for centering. It is not a load issue, it's a concentric/centering issue. And even then, as long as you center the wheel on more than 1 lug nut prior to torquing, it'll be a rare issue if you have a centering problem.
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rsanter
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factory wheels have a centerbore that rides on the carrier hub so that no weight is actually carried by the studs
bob
bob
snorky18
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IIRC are the terms slip-critical connection and shear-critical connection?
shear critical meaning the studs are in shear force, and slip critical meaning the tension of the lugnuts is supporting the weight?
shear critical meaning the studs are in shear force, and slip critical meaning the tension of the lugnuts is supporting the weight?
Schrodingers Cat
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it's 'shear', not sheer
and they do have a shear component, they have to, draw the force diagram...
the load is reduced by clamping/friction, and some designs a center bore hub lip...
it's also why the nut/lug bolts have a conical (ball or taper) surface that resesses into the wheel, to better distribute the forces over a larger area and divert/dilute its direction...
say the weight/wheel is 1000 lbs
the hub may carry most of that, if so equipped, clamping a large percentage, but some still rests on the lug...a 5/8' bolt has shear load capacity > 1000 lbs...but carries a fraction of that...and the load is spread over all the bolts, the %/bolt depending on the number...
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Schrodingers Cat
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just eye ballin' order of magnitude:
say 1/2" shank and 60 kpsi steel
and an adjustment factor of 0.4 for shear, still > 4.5 kip per bolt...
very conservative...
Eds_tls
Well-known member
ha!
I deleted my post after you quoted me.
I sounded too know-it-all-ish so I deleted it. But you're right with everything you said. Wheel studs could easily carry the shear load of a car. But the joint isn't entirely in shear like you said. The friction from the clamp load carries alot of the load as well. Probally the majority
And the 60 Kpsi you quoted is really conserative. Class 10.9 is up around 120 Kpsi tensile if I rememeber right
I deleted my post after you quoted me.
I sounded too know-it-all-ish so I deleted it. But you're right with everything you said. Wheel studs could easily carry the shear load of a car. But the joint isn't entirely in shear like you said. The friction from the clamp load carries alot of the load as well. Probally the majority
And the 60 Kpsi you quoted is really conserative. Class 10.9 is up around 120 Kpsi tensile if I rememeber right
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Schrodingers Cat
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it's good to share your knowledge
especially since it seems to be your area of expertise...
it's how we learn
I'm guessing for a static unit load of 1
hub >0.6 (if equipped)
clamping >0.2
balance shear, very small component
also depends on loading
impulse down on a pothole shear is higher...
sharp cornering, tension and shear swap percentages...
but the system is so over designed, if torqued properly, sound materials, properly prepared threads, it ain't gonna break
pseudorealityx
Well-known member
They don't have to. You're talking about static loads of 1000 lbs. Think about the shear forces the studs "would" see under maximum braking, turning, etc.
No, the ball or taper is used for centering. And not all lug nuts/bolts use that design. As I mentioned previously, Toyotas don't.
http://img.photobucket.com/albums/v80/sakthao/Wheels and Tires/Lug Nuts/02-1.jpg
There's no taper between the wheel and lug nut in this case.
Think about the generic spacers that you can buy at AutoZone, Pepboys, etc. Like these.
http://customwheel.com/custom_wheels/images/wheelSpacers.jpg
The holes aren't matched to the studs/bolts, and they aren't hubcentric. That would mean that if the lugs/studs were really taking shear forces, that the wheel itself would "slip" with respect to the spacer. That doesn't happen, because all shear forces are taken away from the clamping friction between the hub and wheel.
Schrodingers Cat
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they are definitely taking a portion of the total force in shear
the 'have' to...
what would the forces be? most cars can't corner > g, so they would not be in excess of the weight...and that's why they have multipe, each capable of in excess of 5 kip, easy
in addition to centering, the tapered seats gives a much larger area for the forces (shear among them) to be distrubited...you wouldn't want the thread shank to be in shear
the spacers will slip a bit, but the holes are usually oversized so as not to contact the lug bolt and 'shear' them...
shearing a lug is not uncommon if some are loose
movement amplifies the forces in excess of the allowable and they shear...
look at the bolts that were on a loose whell, they are scored around the perimeter
I have a graduate degree in engineering and have a rudimentary grasp of the system...by far no expert, but then again this is basic stuff...
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pseudorealityx
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Ugh...
Of course you break wheel studs if the studs are loose. If that's the case, you don't have clamping force. As soon as the studs see shear, you're overloading them, and they'll eventually break, likely sooner rather than later.
The car I race by the way hits over 1.5+G. Peaks of 1.6 laterally, and 1.1 longitudinally. Any RWD/AWD car with drag slicks on a drag strip is easily going 1+ G at launch.
Another example. http://students.ou.edu/K/Joseph.D.Kliewer-1/pics/Wheel.jpg
Single nut, knock off wheels used on race cars for quicker wheel/tire changes, less hardware/weight, etc.
Online article explaining it: http://images.google.com/imgres?img...en-US:official&um=1&ei=S6kFS6mKAY2SnAed_cTPCw
"The other type of joint is loaded by shear force (Fs). In a joint loaded in shear, the friction between the parts keep them from moving when subject to a shear force. The friction between the parts carries the load, not the fastener. An example of this type of joint would be a shock absorber mount or the driveshaft flange on an airhead. The greater the preload force, the greater the clamping force, the greater the friction, and the stronger the joint. With a properly designed and tightened joint, the bolt will not experience a direct shear load. "
Of course you break wheel studs if the studs are loose. If that's the case, you don't have clamping force. As soon as the studs see shear, you're overloading them, and they'll eventually break, likely sooner rather than later.
The car I race by the way hits over 1.5+G. Peaks of 1.6 laterally, and 1.1 longitudinally. Any RWD/AWD car with drag slicks on a drag strip is easily going 1+ G at launch.
Another example. http://students.ou.edu/K/Joseph.D.Kliewer-1/pics/Wheel.jpg
Single nut, knock off wheels used on race cars for quicker wheel/tire changes, less hardware/weight, etc.
Online article explaining it: http://images.google.com/imgres?img...en-US:official&um=1&ei=S6kFS6mKAY2SnAed_cTPCw
"The other type of joint is loaded by shear force (Fs). In a joint loaded in shear, the friction between the parts keep them from moving when subject to a shear force. The friction between the parts carries the load, not the fastener. An example of this type of joint would be a shock absorber mount or the driveshaft flange on an airhead. The greater the preload force, the greater the clamping force, the greater the friction, and the stronger the joint. With a properly designed and tightened joint, the bolt will not experience a direct shear load. "
I promise you on a properly torqued wheel, virtually all the torsional and radial loads on the wheel are transmitted through the face of the hub via friction. It’s statically indeterminant between the lugs and the hub face, but the hub joint is going to be an order of magnitude more stiff than a stud, thus it carries virtually all of the radial and torsional loads.
On a passenger car, there is no way the clearance between the hub pilot and wheel is tight enough to carry any load. If you have conical nuts, all hubcentric does for a passenger car is insure the wheels were roughly centered when the nuts are torqued. If you only lightly snug the first nut in the torquing sequence, then the wheel has enough freedom to get pretty close to centered when you tighten the second lug nut.
I will make the concession that on VERY heavy trucks they may try to do something with a pilot… like maybe mining trucks, but even then I’d wager pretty good money the primary force transmission path is the hub face.
I’m also an engineer, and get pretty riled up when people who should know better don’t.
On a passenger car, there is no way the clearance between the hub pilot and wheel is tight enough to carry any load. If you have conical nuts, all hubcentric does for a passenger car is insure the wheels were roughly centered when the nuts are torqued. If you only lightly snug the first nut in the torquing sequence, then the wheel has enough freedom to get pretty close to centered when you tighten the second lug nut.
I will make the concession that on VERY heavy trucks they may try to do something with a pilot… like maybe mining trucks, but even then I’d wager pretty good money the primary force transmission path is the hub face.
I’m also an engineer, and get pretty riled up when people who should know better don’t.
Hehehe! Me too....
The purpose, and ONLY purpose of a PROPERLY designed bolted joint is to create clamping force. That clamping force does the work.
Yes, the lugs are under load, but the main thing holding this joint together is the clamp load between the hub and the wheel.
For a hubcentric hub to take any load, the wheel would basically have to have little clamp load allowing the wheel to slip and always rest on the hub. If your wheel is moving, you do NOT have a properly torqued joint.
Schrodingers Cat
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dood, you couldn't even spell shear...twice
it's easy to google stuff, but read all the posts
almost to a man (woman) it's agreed there is a shear compnonent
a single knock-off set-up has the wheel on the hub...and the hub is in shear...
ugh
Schrodingers Cat
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I agree...the clamping force does the majority of the work...
although I've had all lug bolts removed and still could not free the wheel on a BMW...but that is not the centerbores function, although as a consequence of its geometry it does carry a small fraction of the load...
the bolts provide the clamping force, and are under tension (torsional) and shear (radial) loadings...
eventually it's the tire/wheel carrying the load
it's a system, and the loadings are distrubuted over the compnents in varying porportions...and directions