Wheel spacers installed — 400 miles and one muddy trip later

[Jason Miller]

Figured I'd share my experience since there's always somebody asking about spacers on here. I sat on the fence for a while — read every "spacers are

dangerous" thread, and every "been running mine for 10 years" thread — so

eventually I just tried it and found out for myself.

Went with hub-centric 1.5" spacers. Bolted them on in the driveway one Saturday; took about an hour and a half, including the time I spent hunting

for my torque wrench (it was in the shed, where all good tools go to hide). I basically followed BONOSS's Bronco wheel spacer install guide step by

step — clean the hub, seat it flush, star pattern, torque to spec, recheck after 50-100 miles. Their Bronco write-up was way clearer than the usual

"just tighten it good" advice you find on most forums.

400 miles in, including one mud trip that had my wife questioning my life choices: no vibration, no wobble, and both front wheels still attached

(always a plus). Stance looks a lot better too, though the fender gap keeps reminding me I should've bought a lift kit first. Isn't that always how it goes.

Only real advice I've got: recheck the torque after a hundred miles, and don't let anybody talk you into the cheap non-hub-centric ones. Your wheels, your teeth.

Anyone else running spacers on their Bronco? Any long-term thoughts?

 

[jamesroney]

Public Service Announcement Here:

The thing that Guangzhou Zhongpeng Auto Parts Co. DBA "BONOSS" and @Jason Miller calls a "spacer" is NOT a "WHEEL SPACER." In the nomenclature of the aftermarket automotive world, it is called a "Wheel Adapter."

The difference between a wheel adapter and a wheel spacer is a bit of word salad...but it is important to understand. Wheel adapters are structural members that attach to the wheel mounting lugs, and provide new lugs to attach the wheel. Wheel spacers are basically washers, (or a single washer with many holes) to occupy space between surfaces on the original lug studs.

It's confusing, because of course the Adapters shown in the picture above don't actually "adapt" anything. They go from 6x139.7 to 6x139.7. BUT these incorporate their own lug studs. In ENGLISH, they are correctly "spacers." But in Axle speak, they are NOT spacers.

When you translate the English to Mandarin, you do not translate the connotation, or engineering distinction. So it becomes "spacer" and then when they regurgitate the words back, the distinction is lost. These kinds of technical nuances get totally lost in translation. So you just have to do the translation in your head. When they say "spacer" they mean "hub-centric 6-5.5 to 6-5.5 wheel adapter"

A properly installed hub-centric wheel adapter is perfectly safe, and structurally sound. Every GM K3500 DRW truck built from 1988 to 2010 uses a factory installed wheel adapter.

But nobody in their right mind would ever increase the track width on a unit bearing front suspension. Unit bearings are a marginal design at best, and a disaster at worst. Long term, the front wheel bearings will fail sooner, scrub radius is incorrect, and steering arc travel is increased. Far worse, the unit bearing has a very small structural window where the vehicle load can be carried "between the bearings" The design criteria for a unit bearing is to have the force on the wheel be transmitted to the location between the bearings. That is why all unit bearing applications have deep offset wheels. You basically want the center of the tire in line with the center of the unit bearing. If it sticks out, it applies leverage to the bearing, and the bearings wear our exponentially faster. That being said...no one is really using a 6G Bronco off road, and no one is using one as a real truck. So as a glorified station wagon that spends 99% of the time on the boulevard, it will be fine. It will of course be ugly.

 

[ntsqd]

An important distinction to be made about the GM wheel spacer/adapter/thingies is that they are cast steel or cast iron.
The aftermarket such devices are aluminum. Aluminum has a significantly shorter fatigue life. Factor in that the typical spacer/adapter/thingie is a stress-riser nightmare (and there is no better way to design them) and you have two strikes against the common aftermarket spacer/adapter/thingie. When those aluminum spacer/adapter/thingies fail they fail like this:

400 miles means nothing. Come back with X-Ray inspection pictures in 10,000 miles.

I also find it interesting that the OP has exactly one post so far, and it is promoting the product of a company that I've never heard of but whose name frankly sounds like one of Amazon's vendors.

 

[ksagis]

Technical question for ntqsd and jamesrony who are very mechanically inclined

Why does it matter if an adapter is hub centric or not? Seems to me the the bolt up of the adapter to vehicle is located by some extent by both the hub and the lug bolt pattern. Assuming those are both aligned correctly, what does adding a hub centering feature buy you? Seems to me that the force imparted by the bolt torque on lugs swamps things.

And on front locking hubs on EBs, are any of the wheels actually hub centric? And if not, does it matter of the adapter aren’t?

 

[ntsqd]

For years I thought the same thing until one day I realized something. Let's say that the lug studs and the holes in the wheel aren't perfectly matched. Do you tighten one nut at a time, or do you tighten them all simultaneously? Even a slight mismatch pulls the wheel in one direction. That pair of cones is going to center themselves, not the wheel. Depending on how many tightening steps are used it may get pulled in a different direction or may may be too tight for that to happen. In any case the wheel isn't and never will be perfectly concentric by simply tightening the lug nuts.

When I realized this I started watching cars in traffic. Those that I knew were hub centric (late M-B's & BMW's are solid choices to watch) have wheels that spin smoothly, perfectly flat when on smooth pavement. Their axis of rotation doesn't vary in distance from the ground. Those that are lug centric are always just little, ..... "fuzzy" would be one way to describe them. The axis of rotation does vary in distance from the ground as they roll along. It's very subtle, but with practice you can see it. I've been looking for it long enough now that I find it odd that I ever thought that lug centric would of course be perfectly centered. Once you see the difference it becomes very obvious.

If you look closely most wheel hubs do have a narrow hub centric ring on them right up against the WMS.

 

[jamesroney]

Technical question for ntqsd and jamesrony who are very mechanically inclined

Why does it matter if an adapter is hub centric or not? Seems to me the the bolt up of the adapter to vehicle is located by some extent by both the hub and the lug bolt pattern. Assuming those are both aligned correctly, what does adding a hub centering feature buy you? Seems to me that the force imparted by the bolt torque on lugs swamps things.

And on front locking hubs on EBs, are any of the wheels actually hub centric? And if not, does it matter of the adapter aren’t?

So the first hub-centric wheels started showing up around 500 BC. So in a perfect world, they would all be hub-centric. From an engineering perspective, centering on a hub provides a higher probability of concentricity which results in improved NVH. BUT a hub centric wheel results in a higher manufacturing cost. Modern wheel are almost all aluminum, and with the advent of CNC machining, it is trivial to construct an aluminum wheel with an theoretcial center. Keep in mind that there is no actual center in a wheel, and all wheels have a fictitious center. (You can't actually point to the center of a wheel...because it's a hole.)

Once you establish the center, you can machine all other features relative to it. (or really any datum that you like.) On a stamped steel wheel with a pressed insert and welded hoop...there is no manufacturing advantage to a machined bore.

So the prevailing theory is that hub centric wheels are intrinsically more concentric. Now the fact that there are literally billions of miles of successful implementation of lug centric conical seat wheels...the engineering advantage becomes less compelling. There is likely not a significant cost reduction, but possibly not a cost increase. And of course there is the user experience...and if you've ever tried to remove a hub centric f150 wheel that has been used to launch trailers in sea water and welded itself to the axle...you will despise hub centric wheels. Also the lack of a hub diameter standard creates cross-brand compatibility issues. At the end of the day, it's moot. Some Product Manager got promoted, some Six Sigma Green Belt got his cost savings, and hub-centric is the soup of the day.

Yes, once you torque the lug nuts to specification, the entire load could be carried by the flange. But the entire load could also be carried by the hub.
On front locking EB's, nothing is hub centric. and the hubs are machined, so they are mostly round, but the tolerance is piss poor. Once could argue that the errors are additive, so installing the lug centric wheel adapter PLUS the lug centric wheel would increase runout. In the limiting case, if you bolted hundreds of lug centric adapters together, they could certainly end up not-round. But that's true of hub-centric too. Except you are dealing with a potentially much smaller native deviation. So I'm going to say that for small errors, it is trivial. But as the errors become interesting, hub centric will be more reliably round.

 

[ksagis]

When I realized this I started watching cars in traffic. Those that I knew were hub centric (late M-B's & BMW's are solid choices to watch) have wheels that spin smoothly, perfectly flat when on smooth pavement. Their axis of rotation doesn't vary in distance from the ground.

This is a good observation and comment. But is it possible that though the observed MD and BMWs are hub centric, they also other features (like tighter tolerances on lug placement, wheel hole placement, etc) that is also contributing to the observed desirable behavior? Such that it is difficult to determine that is the relative benefit of each contributor? I have worked on various german cars and was amazed by engineering on them.

 

[ksagis]

So the first hub-centric wheels started showing up around 500 BC. So in a perfect world, they would all be hub-centric.

James always brings the best analogies! But were 500 BC devices hub centric because they were not a driven axle and were simply a pulled axle?

My working theory is the value of hub centric is strong function of lug nut profile. Conical lug nuts (and wheels) have little intrinsic benefit from hub centric features since much of centering comes from the lug nuts centering feature. The shoulder lug nuts with a lessor amount of centering feature would benefit much more from hub cenetric.

 

[73azbronco]

this can be fixed easily with proper backspacing.

 

[ntsqd]

This is a good observation and comment. But is it possible that though the observed MD and BMWs are hub centric, they also other features (like tighter tolerances on lug placement, wheel hole placement, etc) that is also contributing to the observed desirable behavior? Such that it is difficult to determine that is the relative benefit of each contributor? I have worked on various german cars and was amazed by engineering on them.

This can be normalized by also observing older M-Bs & BMWs that aren't hub centric, or newer cars with cheap and/or aftermarket wheels on them.

Ford Medium Duty trucks down into the SD's use lug nuts with captured washers and no conic shapes anywhere on the hub centric trucks.

 

[Broncobowsher]

An important distinction to be made about the GM wheel spacer/adapter/thingies is that they are cast steel or cast iron.
The aftermarket such devices are aluminum. Aluminum has a significantly shorter fatigue life. Factor in that the typical spacer/adapter/thingie is a stress-riser nightmare (and there is no better way to design them) and you have two strikes against the common aftermarket spacer/adapter/thingie. When those aluminum spacer/adapter/thingies fail they fail like this:

400 miles means nothing. Come back with X-Ray inspection pictures in 10,000 miles.

I also find it interesting that the OP has exactly one post so far, and it is promoting the product of a company that I've never heard of but whose name frankly sounds like one of Amazon's vendors.

I'll also add in the Aluminum alloy often picked for the spacers is typically picked based on cost and how easy it is to machine. Not how appropriate the material actually is for the application.

And for the '400 miles and all is good', that is a laughable durability check. For a lot of people, that is they didn't fall off the same day I put them on. I've lost track of how many times I have done double that mileage in a single day.

 

[ntsqd]

James always brings the best analogies! But were 500 BC devices hub centric because they were not a driven axle and were simply a pulled axle?

My working theory is the value of hub centric is strong function of lug nut profile. Conical lug nuts (and wheels) have little intrinsic benefit from hub centric features since much of centering comes from the lug nuts centering feature. The shoulder lug nuts with a lessor amount of centering feature would benefit much more from hub cenetric.

I think you might have missed the point that the first conic lug nut tightened centers the wheel on that lug stud. Tightening that first lug nut defines how concentric or eccentric the wheel is going to be until it is removed and put back on. Tightening the rest of the lug nuts isn't going to change that very much. Not without bending that first stud. With an aluminum wheel the other lug nuts are more likely to Brinnell an oval-conic shape into the lug stud holes than they are to move the wheel more toward concentricity. With a steel wheel the lug nuts will simply reach their max torque before fully seating the conic shapes and stop there. Assuming that the bolt circle of the lug studs is actually concentric to the axis of rotation, which is reasonable to expect but unlikely to be exactly that.

If we look at the machine operations involved it becomes clearer (to me anyway) how the studs might not be perfectly centered in the first place. With the raw forging or casting for a hub there is going to be at least three operations to produce it. One to profile the rear of the hub and the bores for the inner bearing and seal, one to profile the outer face and bearing bore (including any hub centric features), and one to produce the lug stud holes and any related spot-facing. The odds of the hub centric feature of the hub being concentric with the bore for the outer race are very, very good because they were machined in the same operation. Where some eccentricity can creep in is that the hub had to be removed from the machine and flipped between the front face and the back face machining. That introduces a potential for the two bearing race bores to be slightly eccentric. Next the hub likely has to go into a different machine to produce the lug stud holes, there's a potential for more eccentricity error. (Not every CNC lathe has live tooling. I would venture that most still do not, but I'm sure that is changing.)
Every time a part has to be removed from a machine you loose the relationship between the part and the machine. You loose what is called the "Triple Zero", that point in space that the machine bases all of it's movements from. Each time it goes back into a machine you have to re-establish that relationship and there are methods for doing this but the error introduced by this is never zero.
Tolerances of size are a whole separate problem, but they don't usually affect concentricity.
All of which is a wordy way of saying that the lug stud holes have an additional layer of location error baked into them that the hub centric feature does not have and we haven't even bolted a wheel to it yet.

 

[ksagis]

I think my process of installing conical lug nuts tends to negate small machining tolerance errors and leads to my school of thought - install all nuts hand tight, wiggle wheel, snug them down again, and then start incrementally torquing. That process would tend to average out small machining tolerance errors on individual lug placement.

Seems like in your machining example, if they sweep the hub to locate after the other machining ops (or have a locating fixture keyed to prior ops), and then do the machine work for the splines for lugnuts, if they have a location error, it’d likely misplace all the holes with a similar offset from centerline.

But it seems like any of the machining tolerances we’re talking about are swamped by the roundness and tolerances on the tires?

 

[ntsqd]

You don't sweep in production, there isn't time for that.

Put a bare wheel on your way and sweep it. Mark the high spot. Then take it off and put it back on the same way and sweep it again. Do the high spots exactly align? I'm betting not.

With a huge (comparatively speaking) sidewall off-road tire the eccentricity of the wheel mounting is likely noise. With the low profile sidewalls used on modern cars it will be significant to NVH and it likely observable in other ways.

 

[jamesroney]

I think you might have missed the point that the first conic lug nut tightened centers the wheel on that lug stud. Tightening that first lug nut defines how concentric or eccentric the wheel is going to be until it is removed and put back on. Tightening the rest of the lug nuts isn't going to change that very much. Not without bending that first stud.

This statement is not factually accurate.

Allow me to demonstrate: In every nascar race until 2022, (and even today in the Busch and Truck) you will witness the pit crew installing FIVE lug-centric conical nuts on to a steel wheel. That nut is touched or tightened exactly ONCE. There is absolutely no doubt that the wheel to hub is not concentric, but subsequent lug nut tightening secures the wheel AND centers it. A typical tire change takes 4 seconds, and then the vehicle is unleashed to the racetrack. This process is called a "pit-stop." There are exactly zero incidents of "bent first studs."

The engineering analysis can be complex, or trivial. If you maintain your Global Coordinate System around the wheel center, the math gets messy. BUT if you translate your User Coordinates to the #1 wheel stud center, the math becomes easy. As you indicate, the first conic lug nut centers the wheel on the #1 stud. BUT after that, all subsequent conical centering efforts result in polar rotations about the #1 stud. There is zero lateral or cartesian forces on the stud, and therefore zero bending moment is applied. From the #1 stud UCS frame of reference, you can only see a rotational force about your own centerline. The amount of force is constrained to 1/2 the amount of displacement allowed by the stud to wheel tolerance. Rotational force applied about a centerline on a threaded fasterner is called Torque. And since the wheel stud / wheel flange / seat area is mostly elastic...You are simply tightening, (or loosening) the lug nut by a degree or two. (I can do the math, but I'm lazy and you can do it better than me. but for a 5 inch bolt circle with 1/16 of slop, the nut will turn something like the inverse sin of .062/5)

So no, they don't bend, and they don't break, and it's fine. 4 tires in 16 seconds. All day, every day.

 

[ntsqd]

If there are no lateral forces how does tightening the other lug nuts result in pulling the wheel from centered on only the first stud to centered on the centerline of the lug stud's bolt circle? I see the torque about the first stud for each successive nut tightened, but being that a torque is a force vector applied at some distance, and that each of those successively tightened nuts contributes another force vector then is the resultant force large enough to elastically or plastically deform the conic seat in the wheel while also being low enough to not put a bending load on any of the studs? That seems highly unlikely, but then those 200 and 300 series Engineering classes found me in the mfg labs learning how to make things instead.

Many times over the years I have experienced an array of flat-head screws where there was a mismatch between bolt hole actual locational dimensions of the countersunk holes vs. those of the threaded holes (tolerances, woe is me!). In all cases tightening any one screw all the way down resulted in at least one of the other screws being unable to fully seat. To get them all something close to flush required the tightening process that ksagis described for tightening his lug nuts. One that does not fully seat each conic pair of surfaces. A common enough practice, but unusual when dealing with lug nuts and certainly not how the Cup Car teams do it because it would take far. far too long.

 

[jamesroney]

If there are no lateral forces how does tightening the other lug nuts result in pulling the wheel from centered on only the first stud to centered on the centerline of the lug stud's bolt circle? I see the torque about the first stud for each successive nut tightened, but being that a torque is a force vector applied at some distance, and that each of those successively tightened nuts contributes another force vector then is the resultant force large enough to elastically or plastically deform the conic seat in the wheel while also being low enough to not put a bending load on any of the studs? That seems highly unlikely, but then those 200 and 300 series Engineering classes found me in the mfg labs learning how to make things instead.

Many times over the years I have experienced an array of flat-head screws where there was a mismatch between bolt hole actual locational dimensions of the countersunk holes vs. those of the threaded holes (tolerances, woe is me!). In all cases tightening any one screw all the way down resulted in at least one of the other screws being unable to fully seat. To get them all something close to flush required the tightening process that ksagis described for tightening his lug nuts. One that does not fully seat each conic pair of surfaces. A common enough practice, but unusual when dealing with lug nuts and certainly not how the Cup Car teams do it because it would take far. far too long.

You are over-thinking it. If the wheel hole “cones” are dimensionally correct, 5x5.5, then centering one and securing it will only allow for rotation about its axis.

You can prove it to yourself by attaching a wheel to a hub with just one nut. (Or worse, try a single mag shank lug). Everything rotates about that shank once it’s on.

And yes, I will now contradict myself as it pertains to countersunk flat head hardware, or multi-fastener sheet metal like an oil pan. We agree that you MUST start each fastener before you tighten any. But that is because you violate the original “concentric” constraint. A flat head screw in a threaded hole is NOT concentric. A class 2A threaded hole gets bonus tolerance in GDT. And the screw gets bonus tolerance too. It’s a minor miracle that anything fits at all. I’ve got a MDA missile flight sequencer here with about 30 flat heads in an aluminum body. And as you say, if you tighten one by itself, it will not go together.

 

[Oldtimer]

VW sand rail spindle mount front wheels are probably the most concentric.

* Sorry ntsqd, but VW bugs are air cooled (actually oil cooled), or they are WCVW, never ACVW.

 

[phred]

I love you guys. Y’all always make me learn stuff in spite of being math deficient. Keep it coming cause I usually just make stuff break it and make it stronger the next time. I quit doing math when I started hiring structural engineers to check my building designs.

 

[ntsqd]

In a way you've proved my point. The first tightened nut dictates where the wheel will be in term of eccentricity. The others merely try to rotate it to be as coaxial to the limits of their applied torque and the geometry will allow. The stud holes and the wheel stud holes are never perfectly positioned. There's always a tolerance on the hole location. Depending on how it was toleranced, and what scheme was used (GD&T Cylindricity? Cartesian X-Y? about 'there'?), and was the inspector hung-over or not, it might be closer to perfect and it may not. I learned a long time ago to assume the tolerances were large enough for the hind end of a South-bound horse to fit thru, that the inspector was hung-over, and that they were using statistical inspection methods where the specific unit giving me the most pain was never actually inspected at all.

Yeah, I get the "OCVW", one need only look at the size of the oil "coolers" used on those engines in an endurance use like desert racing to figure that out, but the common name, correct or not, is "ACVW" and I don't care enough about it to try to correct the masses.