Hub-Centric VS Lug centric (different sizes)
 

Looking into wheel adapters (going from 170mm to 6.5 and need them at 1.5" wide) and i have some questions.

A lot of folks are saying Ford SDs are hub-centric and lug-centric adapters are a no-no. I find it weird since the lugs are conical and will definitely recenter the wheels unless the hub opening on the wheel is EXACTLY the same as the hub step.

Other people mention that the hub step is required for weight support....i've got an H1 that has a GVWR of over 10K and are usually run on factory lug-centric wheels (though hub center ones are also available).

Lastly i just read an ad by an maker of hub centeric adapters and it states that the rear hubs are slightly larger (1 to 2mm) than the front hubs so his adapters (if they were to be used for the rear) would have to be bored out. Okay, well that means if our wheels can be rotated then they also must be at least a few mm larger than the hubs on all the wheels so they can be swapped.... so although an argument can be made that the wheels are hub centeric, it seems at best they are hubcentric only on the rear hubs or maybe they're not hub centric at all? Hub centric wheels are typically flat and use flat lug nuts which allow the wheel to center itself, these don't...

Am i missing something here?

My factory wheels were hub centric (you can tell by the lug nuts).

I believe most stock rims on fords are? dont quote me on that though =)

(ive since replaced them with lug centric rims...but this requires new lugnuts)

perhaps there is something against using lug centric SPACERS on trucks...but im not aware of it....im simply just not a fan of spacers at all.

most articles say that lug centric is a bad idea, as lugs/studs were simply not made to hold the weight of the vehicle...and shearing force is bad...yadda yadda.

id think with all the aftermarket rims and tires on 250s/350s/etc etc...that rims would be falling off all over the place...as im not aware of most folks who install hub spacers on any lug centric rims.

to each his own...while I agree lugs arent designed for that sort of shear force...I think with 8lugs....unless you drop the truck from an aircraft, the weight spread out on 32 individual studs is miniscule compared to the shear limit of the lugs/studs

Funny you should say that. HMMWVs are lug centric and yes they are gently dropped off aircraft. :-X04

If they are hub centric spacers they need to fit very well on the hub and the wheels needs to fit very well on the lip of the spacer also. I think it is easy for Ford to make mass produced hub centric setups while it is easier for spacer companies to make them lug centric. Both methods should work well but they need to be machined exactly right for the application.

Thing is the wheels bolt to the adapters will not be hub centric as they are chevy/dodge. I though perhaps the reasoning would be to center the wheel on the hub. if this is just a shear force farce (you like what i did there? :D) then i won't worry about it.

Just for fun i did a bit of calculation of the shear strength of a single grade 8 (Class 10.9 in metric) 14mm bolt. mind you this is rough and not taking into consideration the minor diameter of the thread but it's just to give an idea.

The shear strength is typically 60% of the tensile strength of the material, so we're looking at 60% of 150Kpsi. A 14mm rod has pi*.551^2 of area sooooo

.6*150000*3.14*(.551/2)^2= 21,698lbs that's each bolt...in a perfect environment. let chop that in half just to take into consideration the threads and a less than perfect condition.... so 10,000 pounds per bolt.....

Anyone ever heard of (8) 1/2" grade 8 bolts being sheared in anything even remotely considered a normal circumstance?

Like I said I don't believe it is a matter of which is better or stronger but a matter of which is easier to make with the least problems. Shearing studs doesn't enter into the equation really.

Yup, i agree. Also just found a page where the figures are all....figured out.

i was a bit off 1/2"-20 grade 8 has a shear of 22.6K while a 9/16"-18 is 28.8K....these bolts are crazy strong and anyone that says the hub centric is safer....well I'd have to hear a good arguement as to why they think 192,000 lbs of shear strength isn't enough on a wheel that MIGHT have a load rating of 3500 lbs....

I'm always looking to learn incase i'm missing something but as far as i can tell the ONLY danger in using a lug centric adapter on a hub centric vehicle is the lugs being not centered to the hub and having it be out of line. easily tested with an indicator when the wheel is off the ground. i used to check my 1pc rims on my hummer as they're notorious for being/getting out of round.

I've ordered lug centric 1.5" spacers :D

I doubt if you would find any lugs being in the wrong place or off center, it's a pretty straightforward machining operation. I would use the lug-centric spacers.

one would imagine the shear issue (or fear) likely stems from cars with 4 and 5 lug (and much smaller studs) hubs....vs heavier duty items.

you know how those "well this one guy knew a guy who had his studs sheared off using lug centric tires" type stories go.

That said, Ive personally had spacers snap studs off and come loose on me...maybe my fear and hatred for them is unwarranted...but its kinda hard to get that out of my mind. (granted it was on an old 1964 pontiac...but the fear would be even greater driving around in the land barge excursion on spacers)

But there are 8 vs 5 lugs and I think they are larger diameter also.

all the spacer horror stories i've heard of involve either 2pc spacers not assembled correctly or (and most common) people not grinding off the lugs on their cars (almost always the car guys) thinking they're flush or less and when they install their wheels over the spacers it's actually sitting (everso slightly) on the lugs. soon as they wear into the wheel with vibration they're loose and sooner or later they loosen enough to either fall or snap off due to the actual bending of the lug not shearing. Also these are pressed into 6061-T6 aluminum which is no-where close to as strong as the bolts. if they're loose and being stressed individually then i have no doubt it would start wearing on that particular area of the aluminum spacer till perhaps the lugs rip through it.

Just seems like a failed spacer is 90% or more user error.

With all that said i'm kinda paranoid as well and the one thing i will most certainly do is apply locktite (blue) to all the spacer nuts when i torque them down. I'm in no way concerned about the strength of the spacer, only that when installing lug nuts onto aluminum wheels or spacers they seem to loosen up on you much more often and on a spacer you'd never know till it was too late. The wheel lugs can just be checked a few times in the first few weeks.