Discussion
doogz said:
I don't recall using the word 'chavs', can you point that out? Thanks.
And the rest of that line was "They seem like a terrible solution to a stupid problem, but then, I've never heard of one fail." which you know, you were just being selective.
Oh you are right yes, it was Disco You, above your post that said that.And the rest of that line was "They seem like a terrible solution to a stupid problem, but then, I've never heard of one fail." which you know, you were just being selective.
doogz said:
GC8 said:
Krikkit said:
Don't forget the bolts aren't holding the weight of the car, just stopping them coming off the spigot.
True for those who used hubcentric spacers. Those who dont understand/didnt/were told they didnt matter will be riding on the wobble bolts, I think...The clamping force is what holds the wheel in place, not the plastic/aluminium/tinfoil spigot ring, or even the centrebore of the wheel sitting over the hub itself, as it's a clearance fit.
If the bolts really are taking the weight of the car, themselves, in shear, you'll not get too far before you have a reasonably drastic accident
'This' advice seems to be prevalent now, but everyone repeating it on forums doesnt actually make it so.
doogz said:
SuperchargedVR6 said:
Just so I understand this correctly, you are suggesting that the wheel bolts themselves don't actually turn the wheel, but rather the clamping force, or friction, between wheel & hub faces? Obviously there are cavaets to this, such as fitters not retorquing the wheel bolts at all, etc?
I must admit, I've greased hub faces on the rear wheels of FWD cars because they never get hot and rust onto the hubs solid. Never had any issues doing this in over 20 years.
Obviously the driven wheels are a different matter, but even then I do see it as a massive issue personally. If it were, shirley the hub faces and corresponding wheel faces slotted, or something?
And expanding on this a little further, what about the 6 little M8 bolts that connect the driveshafts to the inner CV joints on VW Golfs, including the VR6? I can't believe these tightened to ~ 40lb-ft can generate enough friction to cope with ~180lbft engine torque, which is then multiplied considerably in the lower gears? I would say the shear load is very much on the bolts themselves in this case.
M8 bolts aren't exactly little. An 8.8 will take 3.2Te in shear before it fails,. And 40lbft is a reasonably high torque for an M8. The 'standard' tightening torque for an 8.8 M8 is only something like 16lbft. I don't know what your materials are, so can't use a frictional coefficient to calculate the clamping force or anything else useful.I must admit, I've greased hub faces on the rear wheels of FWD cars because they never get hot and rust onto the hubs solid. Never had any issues doing this in over 20 years.
Obviously the driven wheels are a different matter, but even then I do see it as a massive issue personally. If it were, shirley the hub faces and corresponding wheel faces slotted, or something?
And expanding on this a little further, what about the 6 little M8 bolts that connect the driveshafts to the inner CV joints on VW Golfs, including the VR6? I can't believe these tightened to ~ 40lb-ft can generate enough friction to cope with ~180lbft engine torque, which is then multiplied considerably in the lower gears? I would say the shear load is very much on the bolts themselves in this case.
Any idea what the PCD of these 6 little bolts are?
I'm not disputing the theory by the way, I always assumed the shafts / wheels were turned by the bolts. Every day is a school day
A picture paints a goodly amount of words! Ignore the red circled bolts.
Edited by SuperchargedVR6 on Thursday 29th November 16:01
big_boz said:
E500 TAT said:
You can get TUV approved ones so the above does not hold any water.
Bosh, Convinced, Il order some now Edited by AC43 on Thursday 29th November 16:10
SuperchargedVR6 said:
Captain Muppet said:
The friction is generated by the bolt preload. Until that friction is overcome the bolts (and the spigot if there is one) will see no shear load. It's the reason that greasing the hub face makes me shudder.
Just so I understand this correctly, you are suggesting that the wheel bolts themselves don't actually turn the wheel, but rather the clamping force, or friction, between wheel & hub faces? Obviously there are cavaets to this, such as fitters not retorquing the wheel bolts correctltly, etc?I must admit, I've greased hub faces on the rear wheels of FWD cars because they never get hot and rust onto the hubs solid. Never had any issues doing this in over 20 years.
Obviously the driven wheels are a different matter, but even then I do see it as a massive issue personally. If it were, shirley the hub faces and corresponding wheel faces slotted, or something?
And expanding on this a little further, what about the 6 little M8 bolts that connect the driveshafts to the inner CV joints on VW Golfs, including the VR6? I can't believe these tightened to ~ 40lb-ft can generate enough friction to cope with ~180lbft engine torque, which is then multiplied considerably in the lower gears? I would say the shear load is very much on the bolts themselves in this case.
Captain Muppet said:
I first did clamp load calcs when I was designing bits for oil rigs. I wrote the software that calculated tightening torques, clamp loads, load capacities of the joints and the like, backed up with instrumented pressure tests of assemblies with two other guys duplicating and checking my work. The wiki page on bolts does a fair job of explaining how bolted joints work (not for you, obv, but for others reading this it's going to get dull): http://en.wikipedia.org/wiki/Bolted_joint
The clamp load of an M12x1.75 bolt is 13781lb for a tightening torque of 80lbft (though we get more clamp load with the finer pitched threads used on cars). So for a 4x100 PCD and dry friction between aluminium and steel of about 0.6 that gives you 55124lb (245203N) clamp force and 9187lbft (12455N) torque capacity. That'll hold a wheel on, but the values are directly proportional to the friction coefficient of the faces (and the friction of the threads, and the friction under the head of the bolt). Exactly how much safety factor is there is anyone's guess as I'm not even going to try to calculate impact loads.
The only way to load the bolts in shear is when the wheel can move on the face - the holes in the wheel have clearance and there can be no shear load unless the preload or friction has been reduced to zero. So basically when the bolt is undone enough to rattle, and if you have that much movement the bolts are going to rattle free in minutes, and fall out way before shearing. Hubs just aren't designed for the bolts to see shear - it's all about friction. You can load wheel studs in shear as they don't fall out, but the wheel will fall off first. So shear load of the fasteners not only isn't good practice, it's also very hard to do for long without cheating and using threadlock without out tightening the bolts(leading to bolt fatigue) - or else the wheel falls off.
The only other way to directly load the bolts is by assumming the wheel slides around on the hub, in which case then the head of the bolt will move relative to the thread and you'll get bending of a notched bar. Which is exactly the load case you use to break something you can't be bothered to saw through. So again, this isn't a stable engineering solution.
So it's a friction joint. Just like flywheels, and pretty much every other bolted joint on a car.
Head bolts are a special case as they are basically a spring trying to hold the head down without crushing the gasket too much or failing due to differential thermal expansion. Hence head dowels to stop the head wandering around and going all k-seriesy.
The clamp load of an M12x1.75 bolt is 13781lb for a tightening torque of 80lbft (though we get more clamp load with the finer pitched threads used on cars). So for a 4x100 PCD and dry friction between aluminium and steel of about 0.6 that gives you 55124lb (245203N) clamp force and 9187lbft (12455N) torque capacity. That'll hold a wheel on, but the values are directly proportional to the friction coefficient of the faces (and the friction of the threads, and the friction under the head of the bolt). Exactly how much safety factor is there is anyone's guess as I'm not even going to try to calculate impact loads.
The only way to load the bolts in shear is when the wheel can move on the face - the holes in the wheel have clearance and there can be no shear load unless the preload or friction has been reduced to zero. So basically when the bolt is undone enough to rattle, and if you have that much movement the bolts are going to rattle free in minutes, and fall out way before shearing. Hubs just aren't designed for the bolts to see shear - it's all about friction. You can load wheel studs in shear as they don't fall out, but the wheel will fall off first. So shear load of the fasteners not only isn't good practice, it's also very hard to do for long without cheating and using threadlock without out tightening the bolts(leading to bolt fatigue) - or else the wheel falls off.
The only other way to directly load the bolts is by assumming the wheel slides around on the hub, in which case then the head of the bolt will move relative to the thread and you'll get bending of a notched bar. Which is exactly the load case you use to break something you can't be bothered to saw through. So again, this isn't a stable engineering solution.
So it's a friction joint. Just like flywheels, and pretty much every other bolted joint on a car.
Head bolts are a special case as they are basically a spring trying to hold the head down without crushing the gasket too much or failing due to differential thermal expansion. Hence head dowels to stop the head wandering around and going all k-seriesy.
Captain Muppet said:
I'll just click on that link that mrmr96 posted, and find out what I said last time:
No need for the sarcasm. If I had read what you wrote last time, I would have remembered what you wrote last time and not bothered you to hoik out you wrote last time, again, and I must have overlooked the link you mentioned.But thanks, great info
doogz said:
SuperchargedVR6 said:
No idea, sorry! It's not a big PCD. It's been ages since I've worked on one.
I'm not disputing the theory by the way, I always assumed the shafts / wheels were turned by the bolts. Every day is a school day
A picture paints a goodly amount of words! Ignore the red circled bolts.
Well, none of this is likely to be terribly accurate, but here goes.I'm not disputing the theory by the way, I always assumed the shafts / wheels were turned by the bolts. Every day is a school day
A picture paints a goodly amount of words! Ignore the red circled bolts.
Edited by SuperchargedVR6 on Thursday 29th November 16:01
Assume a PCD of 100mm. 6 off Grade 8.8 bolts, a 1st gear ratio of 4, and a diff ratio of 4.
Torque of 180lbft, multiplied by 16, is 3905Nm.
Divided by (PCD/2)*Nbolt is 13020N
Which when divided by the shear area of a M8 bolt (50mm^2) results in a shear stress of 260.33MPa. This neglect the clamping force completely, and still leaves you comfortably inside the allowable shear value of 640MPa for an 8.8 bolt.
All of the above is rough as f
k, and probably wrong, but you get the idea.Thanks to you also!
doogz said:
Muppet, any idea what the ì value for steel on steel, lubricated with copper grease might be?
Hmm. That was 'mu' a minute ago.
Sorry, I'm not at work, so no access to my references.Hmm. That was 'mu' a minute ago.
Google (http://www.engineeringtoolbox.com/friction-coefficients-d_778.html) says steel on steel is 0.8 dry and 0.16 lubricated.
I googled for copper grease and got some sales blurb claiming a friction coefficient of 0.1 but with no other details. I don't trust that.
SuperchargedVR6 said:
Captain Muppet said:
I'll just click on that link that mrmr96 posted, and find out what I said last time:
No need for the sarcasm. If I had read what you wrote last time, I would have remembered what you wrote last time and not bothered you to hoik out you wrote last time, again, and I must have overlooked the link you mentioned.But thanks, great info
Some forums have a weird policy of treating engineering like some kind of offensive elitism, rather than a socially disabling mental disease. It's made me unhelpfully sarcastic.
GC8 said:
doogz said:
GC8 said:
Krikkit said:
Don't forget the bolts aren't holding the weight of the car, just stopping them coming off the spigot.
True for those who used hubcentric spacers. Those who dont understand/didnt/were told they didnt matter will be riding on the wobble bolts, I think...The clamping force is what holds the wheel in place, not the plastic/aluminium/tinfoil spigot ring, or even the centrebore of the wheel sitting over the hub itself, as it's a clearance fit.
If the bolts really are taking the weight of the car, themselves, in shear, you'll not get too far before you have a reasonably drastic accident
'This' advice seems to be prevalent now, but everyone repeating it on forums doesnt actually make it so.
It's all one big can of worms though.
SuperchargedVR6 said:
Captain Muppet said:
I'll just click on that link that mrmr96 posted, and find out what I said last time:
No need for the sarcasm. If I had read what you wrote last time, I would have remembered what you wrote last time and not bothered you to hoik out you wrote last time, again, and I must have overlooked the link you mentioned.But thanks, great info
doogz said:
SuperchargedVR6 said:
No idea, sorry! It's not a big PCD. It's been ages since I've worked on one.
I'm not disputing the theory by the way, I always assumed the shafts / wheels were turned by the bolts. Every day is a school day
A picture paints a goodly amount of words! Ignore the red circled bolts.
Well, none of this is likely to be terribly accurate, but here goes.I'm not disputing the theory by the way, I always assumed the shafts / wheels were turned by the bolts. Every day is a school day
A picture paints a goodly amount of words! Ignore the red circled bolts.
Edited by SuperchargedVR6 on Thursday 29th November 16:01
Assume a PCD of 100mm. 6 off Grade 8.8 bolts, a 1st gear ratio of 4, and a diff ratio of 4.
Torque of 180lbft, multiplied by 16, is 3905Nm.
Divided by (PCD/2)*Nbolt is 13020N
Which when divided by the shear area of a M8 bolt (50mm^2) results in a shear stress of 260.33MPa. This neglect the clamping force completely, and still leaves you comfortably inside the allowable shear value of 640MPa for an 8.8 bolt.
All of the above is rough as f
k, and probably wrong, but you get the idea.Thanks to you also!
Eighteeteewhy said:
I knew this thread would come to this. The centre spigot does take the weight of the car, not the bolts. It is different on a car with studs though.
It's all one big can of worms though.
Yes. They definately design all of the weight of the car to be held on a little 3-5mm spigot with masses of clearance. There's no way they'd make it the full width of the wheel, and taper it to ensure perfect centering, like they do in every other field of engineering, and like they do with knock off hubs.It's all one big can of worms though.
Captain Muppet said:
I first did clamp load calcs when I was designing bits for oil rigs. I wrote the software that calculated tightening torques, clamp loads, load capacities of the joints and the like, backed up with instrumented pressure tests of assemblies with two other guys duplicating and checking my work. The wiki page on bolts does a fair job of explaining how bolted joints work (not for you, obv, but for others reading this it's going to get dull): http://en.wikipedia.org/wiki/Bolted_joint
The clamp load of an M12x1.75 bolt is 13781lb for a tightening torque of 80lbft (though we get more clamp load with the finer pitched threads used on cars). So for a 4x100 PCD and dry friction between aluminium and steel of about 0.6 that gives you 55124lb (245203N) clamp force and 9187lbft (12455N) torque capacity. That'll hold a wheel on, but the values are directly proportional to the friction coefficient of the faces (and the friction of the threads, and the friction under the head of the bolt). Exactly how much safety factor is there is anyone's guess as I'm not even going to try to calculate impact loads.
The only way to load the bolts in shear is when the wheel can move on the face - the holes in the wheel have clearance and there can be no shear load unless the preload or friction has been reduced to zero. So basically when the bolt is undone enough to rattle, and if you have that much movement the bolts are going to rattle free in minutes, and fall out way before shearing. Hubs just aren't designed for the bolts to see shear - it's all about friction. You can load wheel studs in shear as they don't fall out, but the wheel will fall off first. So shear load of the fasteners not only isn't good practice, it's also very hard to do for long without cheating and using threadlock without out tightening the bolts(leading to bolt fatigue) - or else the wheel falls off.
The only other way to directly load the bolts is by assumming the wheel slides around on the hub, in which case then the head of the bolt will move relative to the thread and you'll get bending of a notched bar. Which is exactly the load case you use to break something you can't be bothered to saw through. So again, this isn't a stable engineering solution.
So it's a friction joint. Just like flywheels, and pretty much every other bolted joint on a car.
Head bolts are a special case as they are basically a spring trying to hold the head down without crushing the gasket too much or failing due to differential thermal expansion. Hence head dowels to stop the head wandering around and going all k-seriesy.
The clamp load of an M12x1.75 bolt is 13781lb for a tightening torque of 80lbft (though we get more clamp load with the finer pitched threads used on cars). So for a 4x100 PCD and dry friction between aluminium and steel of about 0.6 that gives you 55124lb (245203N) clamp force and 9187lbft (12455N) torque capacity. That'll hold a wheel on, but the values are directly proportional to the friction coefficient of the faces (and the friction of the threads, and the friction under the head of the bolt). Exactly how much safety factor is there is anyone's guess as I'm not even going to try to calculate impact loads.
The only way to load the bolts in shear is when the wheel can move on the face - the holes in the wheel have clearance and there can be no shear load unless the preload or friction has been reduced to zero. So basically when the bolt is undone enough to rattle, and if you have that much movement the bolts are going to rattle free in minutes, and fall out way before shearing. Hubs just aren't designed for the bolts to see shear - it's all about friction. You can load wheel studs in shear as they don't fall out, but the wheel will fall off first. So shear load of the fasteners not only isn't good practice, it's also very hard to do for long without cheating and using threadlock without out tightening the bolts(leading to bolt fatigue) - or else the wheel falls off.
The only other way to directly load the bolts is by assumming the wheel slides around on the hub, in which case then the head of the bolt will move relative to the thread and you'll get bending of a notched bar. Which is exactly the load case you use to break something you can't be bothered to saw through. So again, this isn't a stable engineering solution.
So it's a friction joint. Just like flywheels, and pretty much every other bolted joint on a car.
Head bolts are a special case as they are basically a spring trying to hold the head down without crushing the gasket too much or failing due to differential thermal expansion. Hence head dowels to stop the head wandering around and going all k-seriesy.
k does that hold itself together?" while reassembling my car, I've never followed it up with reading, for some reason.) Edited by Krikkit on Friday 30th November 17:00
Eighteeteewhy said:
I knew this thread would come to this. The centre spigot does take the weight of the car, not the bolts. It is different on a car with studs though.
It's all one big can of worms though.
Can of worms?? Load of bolleaux, more like! (That's French terminology)It's all one big can of worms though.
If you're going to pretend to be an engineer, you first need to know the difference between a clearance fit and an interference fit.
littleredrooster said:
Can of worms?? Load of bolleaux, more like! (That's French terminology)
If you're going to pretend to be an engineer, you first need to know the difference between a clearance fit and an interference fit.
Oh gawd.If you're going to pretend to be an engineer, you first need to know the difference between a clearance fit and an interference fit.
Fit some spacers to a wheel hub (bolt type) that totally eliminates the centre spigot. Then fit the wheels so it is only the bolts supporting the wheels, then go for a drive.
Eighteeteewhy said:
Oh gawd.
Fit some spacers to a wheel hub (bolt type) that totally eliminates the centre spigot. Then fit the wheels so it is only the bolts supporting the wheels, then go for a drive.
My rally Mini was so equipped in 1978 so that the front wheels would clear the (Viva?) calipers. The only downside was that it ate wheel bearings because of the extra offset.Fit some spacers to a wheel hub (bolt type) that totally eliminates the centre spigot. Then fit the wheels so it is only the bolts supporting the wheels, then go for a drive.
The spigot is clear of the hole - in engineering terms, it is a massive clearance fit (Google it), and in any case, the centre of a basic wheel is a lump of rolled mild steel with a bloody great radius; how the hell can that locate anything other than loosely for wheel-fitting purposes? It isn't even machined!
If you want to locate and centre something rotating with any degree of accuracy, you have to use either a taper or a very accurately machined hole-and-spigot set-up. Wheel bolts (or nuts) are tapered for this reason, and to provide a locking function for the bolt on the taper.
The wheel is secured and driven by the frictional clamping forces as previously discussed.
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