Swapping alloys for steel wheels, use same bolts?
Discussion
SuffolkIan said:
Why? How do you expect to correctly torque bolts without lubrication?
Ian,I'll try to explain.
The mechanism here is that the wheel and hub are clamped together via a high friction mating surface pair by bolts that provide sufficient clamping force. When clamped, there must be no rotational movement under braking, acceleration, bumps or whatever.
1. Lubricating the bolts.
The bolts will provide the correct clamping force when torqued to the correct torque when dry. If you lubricate the bolts and torque up to the same torque value, the force in the bolts will be much much higher. This could/will result in snapped or stretched bolts, stripped threads on the bolts or stripped threads in the hub. Sod's law dictates that it's the hub that strips first.
2. Any lube on the mating surfaces.
If the friction between the mating surfaces is reduced, then there may be rotational slippage. This could cause your bolts to shear off.
There's a clue - no lube on these bits from the factory. I know it's a bore (and unsightly) having to deal with the minor corrosion, but a couple of whacks on the wheel beats sheared bolts or detached wheels.
I understand your point of view, however it contradicts everything I have ever been taught about making up a bolted assembly where a specific torque value is required.
I wouldn't recommend lubricating the face between wheeel and hub but the face between bolt mating surface and wheel should be according to everything I have learnt. I even have charts to calculate the correct torque dependent on the lubrication factor of the specific lubricant being used.
Ian
I wouldn't recommend lubricating the face between wheeel and hub but the face between bolt mating surface and wheel should be according to everything I have learnt. I even have charts to calculate the correct torque dependent on the lubrication factor of the specific lubricant being used.
Ian
Yep, and the correct torque here is the dry torque not the lubricated torque.
In theory you could go your own way and wing it by estimating the reduced torque needed for lubricated bolts. I still think this is introducing an unnecessary risk as the lube will increase the chance of head slippage which (in an environment with high vibration) could lead to bolt loosening. All that friction in a dry assembly is chosen for good reason.
The manufacturer will have done plenty of testing (ultrasonic) on the assembly to make sure it works well. I, for one, would strongly advise not to significantly modify an assembly as critical as the one that keeps your wheels on!
In theory you could go your own way and wing it by estimating the reduced torque needed for lubricated bolts. I still think this is introducing an unnecessary risk as the lube will increase the chance of head slippage which (in an environment with high vibration) could lead to bolt loosening. All that friction in a dry assembly is chosen for good reason.
The manufacturer will have done plenty of testing (ultrasonic) on the assembly to make sure it works well. I, for one, would strongly advise not to significantly modify an assembly as critical as the one that keeps your wheels on!
apotts said:
Yep, and the correct torque here is the dry torque not the lubricated torque.
In theory you could go your own way and wing it by estimating the reduced torque needed for lubricated bolts. I still think this is introducing an unnecessary risk as the lube will increase the chance of head slippage which (in an environment with high vibration) could lead to bolt loosening. All that friction in a dry assembly is chosen for good reason.
The manufacturer will have done plenty of testing (ultrasonic) on the assembly to make sure it works well. I, for one, would strongly advise not to significantly modify an assembly as critical as the one that keeps your wheels on!
Have you any evidence to support all that? I know for a fact that, and I know this is relevant to CVs and not specifically cars, the frequent episodes of wheels coming off trucks and buses some years ago led directly to the IRTE (Institute of Road Transport Engineers) developing a method of fitting road wheels which specifically advised lubricating studs and nuts and applying a thixotropic grease to the hub face. This was endorsed by several manufacturers. It's all in a book called 'The lost wheels mystery". In theory you could go your own way and wing it by estimating the reduced torque needed for lubricated bolts. I still think this is introducing an unnecessary risk as the lube will increase the chance of head slippage which (in an environment with high vibration) could lead to bolt loosening. All that friction in a dry assembly is chosen for good reason.
The manufacturer will have done plenty of testing (ultrasonic) on the assembly to make sure it works well. I, for one, would strongly advise not to significantly modify an assembly as critical as the one that keeps your wheels on!
One of the key points of that investigation was that correct clamping forces can be better achieved with lightly lubricated studs/nuts.
I again acknowledge that this refers to CVs but I would think the principles are applicable.
It's well known that a lubricated system will give a smaller clamping force numerical distribution, so clearly lubricated is "better" when trying to be accurate. I think there are other factors in play though, like size of fixing, cost, environment, acceptable force range and so on. It seems most car manufacturers go for a dry system and most CV manufacturers a wet system. Looking at the latest IRTE document they too are saying exactly the same as me: the lubrication and torque must be as per the manufacturer. My experience away from cars is with bolting much larger than CV wheel bolts (and pressure retention systems, rather than torque transmission).
My point, at this level (PH), is that if you lubricate wheel bolts and tighten them to the dry torque, then you may do a lot of damage (YP of bolts, thread damage, risk of wheel separation etc). If you don't lubricate bolts and tighten them to the wet torque then you may not achieve the desired clamping force and do damage again.
I have never heard of a rigid clamped friction joint being lubricated before, thixotropic or otherwise! That IRTE advice lists lubricated mating faces as a reason for wheel separation (Quote: "incorrect lubrication, eg applied to the mating surfaces of wheels").
As for evidence? You are simply changing K from about 0.2 to about 0.16 in the bolting formula when you add lube. Obtain the higher bolting force and weep! Evidence for "friction helping to prevent loosening" is something I am not well versed in, so have a look here, and I accept that this Jost effect is outside of my experience.
My point, at this level (PH), is that if you lubricate wheel bolts and tighten them to the dry torque, then you may do a lot of damage (YP of bolts, thread damage, risk of wheel separation etc). If you don't lubricate bolts and tighten them to the wet torque then you may not achieve the desired clamping force and do damage again.
I have never heard of a rigid clamped friction joint being lubricated before, thixotropic or otherwise! That IRTE advice lists lubricated mating faces as a reason for wheel separation (Quote: "incorrect lubrication, eg applied to the mating surfaces of wheels").
As for evidence? You are simply changing K from about 0.2 to about 0.16 in the bolting formula when you add lube. Obtain the higher bolting force and weep! Evidence for "friction helping to prevent loosening" is something I am not well versed in, so have a look here, and I accept that this Jost effect is outside of my experience.
OK, having done some research it seems I need to offer my humble apologies. It would appear that it is generally specified that wheel bolts be made up dry. Looks like I have a cleaning job for the weekend!!
I would add that it is very important to ensure wheel bolts are clean and free of corrosion or grit before re-use.
Ian
I would add that it is very important to ensure wheel bolts are clean and free of corrosion or grit before re-use.
Ian
SuffolkIan said:
I understand your point of view, however it contradicts everything I have ever been taught about making up a bolted assembly where a specific torque value is required.
Ian
Ian,Ian
On my BMW (F10) the recommended torque is 140 NM, dry. That will give a load in the bolt of around 50 KN, which is what BMW have calculated what is needed, and what the bolts can handle. Add lube and torque to 140 NM, and the force in the bolts will be around 63 KN. Maybe higher. Are you feeling lucky?
Remember, correctly installed bolts are already stretching.
EDIT: Ian, I wrote the above, posted, and then saw your reply! I'll leave it up - not for you but for anyone else reading in the future.
pauldavies85 said:
Torque setting for wheel bolts? Modern times
Surely it's just pretty tight but not ridiculous mate.
Not had a wheel or even a single bolt loosen yet! I always thought it was common perception that wheel boots get done up too tight?
Modern times? The laws of physics didn't disappear just because we're in the 21st century! Torquing things correctly is much more importantly than you think. The correct torque makes sure the wheel doesn't warp, while stretching the bolt just enough to make sure it holds without damaging it or the other surfaces. For wheels it might not be quite as critical as for the bolts holding your crankshaft down, but it's still important to get it right. Not only that, but you should re-torque your wheel bolts after a couple of hundred miles. Plenty of accidents have been caused by wheel bolts working loose because someone thought "pretty tight" was tight enough.Surely it's just pretty tight but not ridiculous mate.
Not had a wheel or even a single bolt loosen yet! I always thought it was common perception that wheel boots get done up too tight?
Ok, ill be honest, I do understand some of the physics more than I let on.
Are the torque settings not just a safety net to ensure people do the bolts up enough and law suits don't follow?
Do they really analyse the stretching of the bolts and warping of the wheels at varying speeds?
Or is it more the sheer point of a given bolt or more importantly the torque that will strip the bolts?
Seeing as up your mating too very hard surfaces doing something pretty tight (as in not all yr body weight) I guess will be about the same as the torque range recommended - I'm going to get my torque wrench on mine and check over the weekend! Lol
I still stand by a dab of old copper grease. Even my winter bolts driving in the alps etc didn't get too corroded.
Are the torque settings not just a safety net to ensure people do the bolts up enough and law suits don't follow?
Do they really analyse the stretching of the bolts and warping of the wheels at varying speeds?
Or is it more the sheer point of a given bolt or more importantly the torque that will strip the bolts?
Seeing as up your mating too very hard surfaces doing something pretty tight (as in not all yr body weight) I guess will be about the same as the torque range recommended - I'm going to get my torque wrench on mine and check over the weekend! Lol
I still stand by a dab of old copper grease. Even my winter bolts driving in the alps etc didn't get too corroded.
pauldavies85 said:
Ok, ill be honest, I do understand some of the physics more than I let on.
Are the torque settings not just a safety net to ensure people do the bolts up enough and law suits don't follow?
Do they really analyse the stretching of the bolts and warping of the wheels at varying speeds?
Or is it more the sheer point of a given bolt or more importantly the torque that will strip the bolt thread?
The bolts shouldn't be taking shear at all, and you're more likely to strip the threads if you lubricate them.Are the torque settings not just a safety net to ensure people do the bolts up enough and law suits don't follow?
Do they really analyse the stretching of the bolts and warping of the wheels at varying speeds?
Or is it more the sheer point of a given bolt or more importantly the torque that will strip the bolt thread?
pauldavies85 said:
Are the torque settings not just a safety net to ensure people do the bolts up enough and law suits don't follow?
No, the torque setting (singular) combined with the lubrication state of the bolt will give the correct load in the bolt. Load too big = stretched/snapped bolt/stripped thread (and detached wheel), load too small = hub slippage, bolt loosening, detached wheel.pauldavies85 said:
Do they really analyse the stretching of the bolts and warping of the wheels at varying speeds?
Clamping load and bolt force, yes. Wheel warp?pauldavies85 said:
Or is it more the sheer point of a given bolt or more importantly the torque that will strip the bolts?
I think you mean yield point. The torque is only there to create a force in the bolt. Force too great - see above (etc).pauldavies85 said:
I still stand by a dab of old copper grease. Even my winter bolts driving in the alps etc didn't get too corroded.
You won't worry have to worry about corrosion when your copaslip has created an excess load in your bolts and they do this:http://www.bimmerforums.com/forum/showthread.php?1...
And secondly... Even the BMW manuals now state to not use ANY grease on the mating surfaces, but use a touch on the very outer edge of the hub, to prevent any sticking etc
Copper grease is not a good idea; mating surfaces need to be absolutely spotless to allow full contact with no interference and also for heat dissipation etc
That's why 'quick job' powdercoated alloys need to have the mating surfaces cleaned/sanded back to remove the powdercoat
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