Torque on Wheel Studs 4

[mjgarrin]

Hello, there is probably a simple answer to this, but i have not been able to find it.

I am familiar with the idea that the max available torque from a wheel is dependent on the static load radius, load on the wheel, and the friction between the wheel and ground.

I am tying to determine the load path of this torque to the wheel studs. In the example picture, there are 5 wheel studs.

I know the studs see vertical loading evenly. So with 5 studs, each stud sees a vertical load equal to “W/5”.

Would the torque be distributed evenly between these 5 wheel studs?
If a take the bolt circle of the wheel studs, would dividing the wheel torque by the bolt circle radius determine the shear force acting on the wheel stud?
Or does a strong clamp load prevent the studs from seeing any torque or shear loading, and the torque is simply distributed to the hub?

Thanks!
Mike

 

[LionelHutz]

To be fair, salty northern roads often create an interference fit between aluminum wheels and the steel shoulder. Its the main reason every decent tech or shop has a long handle 20'ish lb deadblow.

So? It wasn't designed that way and isn't necessary to keep the wheel on the vehicle.

You could argue that lugs nuts don't need re-torquing in the north because they rust on too then....

 

[3DDave]

In the north they often don't need re-torquing because the tire shops set the impact wrenches high enough to spin the studs.

 

[Lou Scannon]

I've removed lug nuts that were partially friction welded to the wheel due to overzealous use of the impact wrench. So much for the conical seat.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[IRstuff]

I recall one time, I had to use a 2 ft extension to break free lug nuts from a tire I needed to change

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[TugboatEng]

I keep a 1/4 ton lever hoist in my tool bag for those pesky fasteners and fittings.

 

[CWB1]

So? It wasn't designed that way and isn't necessary to keep the wheel on the vehicle.

No, but it could lead someone to believe the wheels were interference fit as corrosive growth alone will often keep a wheel on. I have seen several folks (including myself) drive miles with loose lugs to no avail in an effort to break stuck rears free when a large deadblow wasnt available.

 

[LionelHutz]

Again. So? I doubt that would happen on a Corvette so why is it relevant to my post or the discussion about wheels not being designed to have an interference fit which means they can't ride on the center hub while in service?

 

[CapriRacer]

I may be one of the few people who post here who has direct knowledge about whether wheels are an inference fit to the hub - they are not!

I am a retired tire engineer who used to call on Ford, and later I worked in Quality where GM would do an audit of our tire return procedures. In both cases, vehicle vibrations were a common topic and I learned how vehicle manufacturers deal with the problem - and one of those was hub centering.

While the fit is close (and I can't quote clearances - too long ago!), and the fit was a taper (can't remember the angle), it was enough that being off center didn't result in a significant force being generated. To me that means 2 or 3 thousandths of an inch of clearance. I say that because my experience with wheel runout and tire uniformity says that 0.001" ~= 1# force variation, and to be insignificant, it can only be a few pounds.

Given that GM's spec for force variations was as low as 8#, the wheel/hub clearance has to be in that range.

 

[Kim_W]

There is always a bit of clearance between the hub shoulder and rim center hole and certainly no direct contact (at least for modern BMW vehicles). Enough clearance that the hub shoulder is going to corrode a bit during operation, this is quite normal to see. As a result mechanics usually (abrasively) clean it during a shop visit, and a very small amount of copper grease is applied. Although the grease is not officially recommended by the OEM as it may among others influences the friction coefficient at wheel/hub contact.

My experience (modern BMW's) tells that the hub shoulder is there to assist the mechanic during the disassembly/assembly of the wheel. It would be a real challenge for the mechanic to assemble the wheel (tightening of the bolts) if there was no shoulder. This will lead to longer replacement times (and the need for wheel lifting device) AND a lot of thread damaging = No Go.

Again, centering of the wheel on (at least modern BMW vehicles) is done by using tapered wheel bolts.
The second function of the wheel bolt is to provide enough clamping force to meet all extreme conditions the car will ever see (safety factor included). If correctly installed, the bolts ONLY provide clamping force. This total force, combined with the friction coefficient of the hub/wheel interference will always be higher than the max dynamic/static load the wheel will see in extreme conditions.

Best regards,
Kim W
Former BMW technician

 

[TugboatEng]

Copper on aluminum? You should suggest a silicone grease to anybody partaking in that practice.

 

[snookluvr]

I'll share an unfortunate occurrence that hopefully can be used as a "lessons learned". First, my background.

I am a retired structural engineer so I have considerable experience with high strength bolt tightening in bearing and slip critical connections for buildings. I used direct tension indicating washers (DTI's) many times to ensure adequate bolt preload for structural connections. The old adage, bolt torque is not synonymous with preload is very true. Also, as a teen, I grew up around cars, worked in a service station for a couple of years and changed hundreds of tires.

I have a tandem axle boat trailer that gets dunked into saltwater frequently so I thought it would be a good idea to coat the wheel studs and aluminum wheel to steel hub contact surface with anti seize compound. The wheels are lug centric wheels as most trailer wheels are. They were unbalanced because I could not find a tire retailer that could balance lug centric wheels (I have since found Costco to do it). I didn't torque the lug nuts but I tightened them very well from past experience.

A few days ago in a very early morning interstate trip, I experienced a lot of trailer vibration. I stopped and checked the tires as best I could because it was dark and the I75 was very busy. I saw nothing wrong.......BIG MISTAKE. Several miles down the road I lost a wheel. In hindsight, I should have checked the lug nut torque. I was in disbelief that this could happen to me. I though I had all of the bases covered. Fortunately I didn't hurt anyone and there is a wheel somewhere in the weeds of the shoulder of I75.

I will note what I think were several mistakes made:

1. Don't use anti seize compound on the hub to wheel surface because it will decrease the friction required for a good shear connection. As far as anti seize on the studs, I guess that's debatable. Owners manuals for the vehicles say not to use anything on the studs. I don't know how you get the proper preload on automotive bolts/studs with unknown thread and contact surface coefficients of friction??? I know in my profession, there was strict quality control on fasteners to prevent corrosion. Still, measures like DTI's are used to ensure proper bolt preload.

2. Get hub centric wheels balanced to minimize vibration. Don't accept that blank stare from the tire tech. Find someone that can do it properly.

3. Always check and re torque the lug nuts, if necessary, after driving 25? miles. That would have most likely prevented my situation.

 

[LionelHutz]

I know someone who has put many thousands of wheels back onto vehicles with a coating of anti-seize between the wheel and hub after clean the corrosion off both. He hasn't had a wheel fall off yet.

 

[NormPeterson]

3. Always check and re torque the lug nuts, if necessary, after driving 25? miles. That would have most likely prevented my situation.

This, though the miles driven might vary a bit.

Which reminds me, I should retorque the lug nuts on the car I recently swapped the "3-season" tires off of for the cold weather set. Virtual little pink star for that, snook.


Norm

 

[Tmoose]

On Sept 20 Someone way smarter than me said this.
"Assuming mu is 0.3 (Five 1/2" studs torqued to 90 lb-ft) gives a factor of safety of 2 or so on the force required to rip the suspension out of the car and incidentally smash the wheel up completely in the square edge pothole test."
If antiseize on the wheel-hub faying surfaces reduces the coefficient of friction by 2/3 it would seem there is still little chance of a couple thousand pounds of rotating shear force causing things to shift.
Not a bad trade off for this New Englander/Mass-hole.

Those fancy alloy wheels have a rep for initial stud loosening even when assembled dry, thus demanding torque checks shortly after installation, especially on large over the road trucks. I attribute that loosening to no springy-ness in the joint as provided by the built in massively heavy duty belleville effect of typical convoluted steel wheel in the stud area.

 

[CapriRacer]

snookluvr (Structural) said "..... 2. Get hub centric wheels balanced to minimize vibration. Don't accept that blank stare from the tire tech. Find someone that can do it properly. ...... "

It is my understanding that even lug centric wheels have a reasonably centered centerhole - and that balancing using the centerhole would be much much preferable to not being balanced at all.

 

[snookluvr]

The sheet that came with the wheels specifically required lug centric balancing. See the attached link.

https://www.youtube.com/watch?v=ocWAZqNGhM4

I realize you could do a thesis on this subject but the way I see it is as follow:

1/2" x grade 8 stud, fine threads = proof load of 19.2k. Just assuming 5 lugs with a coefficient of friction of 0.1 = 9.6k shear resistance. I agree this is considerably more load than that wheel will ever see. The wheel, tire, and bearing will fail before anything near that load is reached.

The debate is how much preload you can achieve when so much is unknown about fastening friction. I understand you mechanical folks may use the equation T=KDF where K is the friction coefficient that can vary from 0.1 - 0.3??

https://www.fastenal.com/en/83/torque-calculator

The above link seems to suggest about 90 ft-lb for a lubricated stud.

Oh, the lug nuts on my trailer are SS, another different K value. Like I said, you could do a thesis on this. Someone surely has.

 

[GregLocock]

At work we get very fussy about wheel balancing, both in production and at the proving ground. Our wheels are lug centric, but that doesn't mean that big hole in the middle is randomly placed, it is fine for balancing purposes, and is of course the main datum for machining alloy wheels. One of the reasons for using lug centric is that customer delight is not increased when they find that they can't change a flat because the wheel is effectively welded to the hub by corrosion or grot.

Cheers

Greg Locock


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