Wheel bolt, hub, load physics

[rage2]

First I’ll admit that I’m not sure who’s right here, but a beer bet between my brother and I are resting on this debate. The 2 arguments are:

1. The weight of the vehicle sit on the hub or bolts depending if it’s a hub centric wheel or lug centric wheel.

2. The weight of the vehicle and forces of driving are evenly distributed on the surface of the wheel and hub where its mounted, and the hub center is only used as a centering device and bolts used to clamp down both surfaces to ensure that the surfaces do not slip. Only if there is movement between wheel and hub would transfer load to the hub center and/or bolts.

Anyone with solid physics can help us sort this out?

[ercchry]

Sounds like a strength of materials question... wasn’t a huge fan of that class and it’s been 10yrs... but googling that might help get you on your way for where the loads are

[rage2]

We’ve googled all morning. Seems nobody is dumb enough to argue about this haha.

[Sugarphreak]

...

[ercchry]

^^ah, there is a better answer from a current student haha

Well I can tell you that the nature of bolts, they are very weak when loads do not transfer through them correctly... they are there to clamp the two surfaces together, once clamped together the wheel face and hub face will act as one and share the load, transferring it to the strut/spring. We know this is true vs the lugs carrying anything cause of the simple fact that they will sheer off if loose cause if they are loose, they are not clamping the wheel to hub anymore

To demonstrate this in an academic way, you’d need to draw a diagram, with the direction of the forces, and solve them all... which would probably take about 20min for someone to solve that knows what they’re doing haha

[ExtraSlow]

Those are good answers, and they sound correct to me. So I guess the friction between the two surfaces is what's carrying the majority of the load and the tension of the bolts is what's ensuring that friction.

So answer #2 wins.

[lilmira]

Let's say 1000lbft of torque at the driveshaft, that's more than plenty for most cars. Lug bolts are may be a few inches from the center of the wheel. Lets say 3 inches, that's 1/4ft. So the shear force at the lug bolts is 4000lb. That's not a whole lot for the bolts. A mid grade 1/2" bolt will take 8-9000lbs and that's just one bolt. I can't say for sure about the friction carrying all the torque but the bolts for sure can take it. With modern day machining, I think the holes are pretty well aligned with the bolts. Then you have the cone/ball seat so that all the bolts are pretty much ready to load. One reason to torque your nuts/bolts is to prevent them from backing out on it's own especially with moving parts. The bigger the bolt, the bigger the torque. That's just good practice at the minimum.

[Darkane]

Let's say 1000lbft of torque at the driveshaft, that's more than plenty for most cars. Lug bolts are may be a few inches from the center of the wheel. Lets say 3 inches, that's 1/4ft. So the shear force at the lug bolts is 4000lb. That's not a whole lot for the bolts. A mid grade 1/2" bolt will take 8-9000lbs and that's just one bolt. I can't say for sure about the friction carrying all the torque but the bolts for sure can take it. With modern day machining, I think the holes are pretty well aligned with the bolts. Then you have the cone/ball seat so that all the bolts are pretty much ready to load. One reason to torque your nuts/bolts is to prevent them from backing out on it's own especially with moving parts. The bigger the bolt, the bigger the torque. That's just good practice at the minimum.

Bigger stud and nut bigger torque correct.

Ford recommends 150 lb ft for the Gt350 lugs.

I remember some of this stuff from a mechanics course I took a few years ago.

The PCD * number of studs * area of studs ... something something. Lol.

[HiTempguy1]

The reasons you torque the bolts is to add tension. That compresses the wheel against the hub surface, and that friction created along that surface is tremendously huge. That is essentially what holds your wheel firmly onto the hub and keeps it from moving at all.

What you are talking about in the other scenario is having the bolts in shear, which firstly they are not very good for; or using the hub in shear, which again isn't very good. The bigger issue is that the tolerances of the holes (both for installation and allowing for thermal expansion) would mean your wheel would be moving all over the place if you did this.

Generally speaking anytime you tension a bolt by torquing it down, you are changing the connection to a slip-critical one that relies on the friction between the two surfaces

https://en.wikipedia.org/wiki/Slip-critical_joint

I believe that hub-centric just refers to using the hub to centre the wheel during mounting. Hub-centric rings for instance would be used when the diameter of the hub is much smaller than the bore of the wheel. You could never really rely on the hub for bearing strength simply because the tolerances between the hub and wheel must exist (installation & thermal). It would be a pretty shaky ride, and the constant hammering on the bolts would shear them off pretty quick, haha.

I'm actually going to save a copy of this, because you put it all into clear wording so well. Every god damn time you have to explain this to someone arguing otherwise in a verbal fashion, its difficult. I'm just going to shove this in their face and tell them to read it.

[Sugarphreak]

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[lilmira]

I haven't stayed at the holiday inn express for a while so that's as much as I can contribute. Slightly related, do you remember that one mythbuster episode wit the square wheels, I think they managed to shear the bolts off lol.

[spikerS]

I haven't stayed at the holiday inn express for a while so that's as much as I can contribute. Slightly related, do you remember that one mythbuster episode wit the square wheels, I think they managed to shear the bolts off lol.

Yes, the bolts did shear, but because the tire is square, it is basically a jackhammer on those studs, and given enough time subjected to that, any bolts will shear just like in the video. Replace them with proper round tires, and there is no repeated impact, and thus, the bolts are never subjected to those repeated impacts.

[rage2]

I knew someone here would be able to use their physics know how to answer this. Thanks haha.


Yes, the bolts did shear, but because the tire is square, it is basically a jackhammer on those studs, and given enough time subjected to that, any bolts will shear just like in the video. Replace them with proper round tires, and there is no repeated impact, and thus, the bolts are never subjected to those repeated impacts.
Ya in that case if the friction is strong enough between the wheel and hub surfaces, the bolts wouldn’t have sheared off. It’s the movement of the wheel and hub surface that causes that jackhammer load on the bolts and subsequently shear them off.