Off Center Boring of Automotive Wheels 3

It does not make sense to me to intentionally bore off-center. Marking the heavy spots of the wheel and tire makes sense to minimize the amount of correction required by weights by matching the marks correctly.

Balancing won't prevent the runout of an off center tire. Radial stiffness of the tire will then create a variable load.

CapriRacer said:

Some time back some vehicle manufacturers would have their wheels purposely built off center and marked for the low point

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I think you're confusing balancing marks with centering. They aren't the same. No one intentionally machines pilot bores off center.

I honestly can't recall the last time I saw a new light-duty vehicle with hub-centric wheels stateside. Medium & heavy-duty yes, light-duty no.

Are the conical/tapered lug holes also machined off-centre in this idea?

If the bore moves, but the lug holes do not, then that offset would created unwanted stresses in the lug studs.

Were the lug nut seats flat in this idea?

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If a wheel's off-centre bore was matched to an eccentric tire, you would never be able to (sensibly) replace a worn-out tire. This seems unlikely.

"I honestly can't recall the last time I saw a new light-duty vehicle with hub-centric wheels stateside. "

Hmm. What would cause wheels to become stuck on the hub ?

Aftermarket wheels often have oversized hub bores so that they can fit s wider range of vehicles.

It was certainly done in the 90s, as you say to cancel first order tire force variation. I haven't 'done' wheels since then.
Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

Matching tire and wheels relative to each other is a horse of a different color compared to purposefully machining hub centering bores off center. One happened without a doubt (and still happens today). The other did not.

Wow, so many responses!

But clearly there are some misconceptions.

First, I am a tire engineer - retired. At one point in my career, I interacted with Ford Light Truck Engineering in Dearborn. It was there that I learned about off-center boring.

And perhaps off-center boring is a misnomer. It's quite possible the center bore (and lug holes) are used to machine the rim flanges off center. I do not have direct knowledge of wheel manufacturing processes, so can't comment on how this was done.

Tire uniformity and tire balance are 2 separate things. We are all familiar with tire balance, but tire uniformity is a bit obscure and not well known. Google "Tire Uniformity".

Greg Locock confirms both the existence of off-center boring and the timeframe I remember it from. Thanks, Greg.

Given the improvements in tire uniformity since then, I strongly suspect off-center boring isn't done nowadays. I am seeking confirmation of this. I want to be able to point at the past practice of matching the tire high point with the wheel valve hole and say with confidence that this isn't how things are done nowadays - with a story as to why this is a thing that is still present on the internet.

And just an FYI: There isn't any commonality about marking the high point of tires - both from OEM's and tire manufacturers. And I have done a brief survey of car dealers and it's also clear there is no commonality as to how the wheel low point is marked and it's not at the valve hole.

And just to complete the picture: Here's my webpage of Tire Balance, Uniformity, and Vibration Link It was written 15 years ago and I want to update and reorganize the information presented.

Were wheels produced with a single (nominal) dimension of runout (perhaps optimized for a certain statistical variation of tire uniformity), or were there different part numbers, with each part number having a slightly different runout dimension?

pmbrunelle said:

Were wheels produced with a single (nominal) dimension of runout (perhaps optimized for a certain statistical variation of tire uniformity), or were there different part numbers, with each part number having a slightly different runout dimension?

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None of the above.

Wheels were produced using standard processes, which result in wheels which are/were imperfect. Each wheel would be measured as needed to identify if runout is within spec. If it isn't, the part is scrapped, and if it is, the part is marked accordingly (or not at all, if that's the manufacturer's method) to identify the location of highest runout.

Greg's linked Jaguar document talks about match mounting of tires - which happened 30 years ago and still happens today depending on manufacturer. That process says nothing about, and has nothing to do with, how the wheel is machined.

No one purposefully machined pilot bores off center.

Posted by pmbrunelle: "Were wheels produced with a single (nominal) dimension of runout (perhaps optimized for a certain statistical variation of tire uniformity), or were there different part numbers, with each part number having a slightly different runout dimension?"

Here is my understanding: Each tire manufacturer would submit average and standard deviation for the tires they were supplying. The wheels were specified with a given offset and an allowable runout range from that offset. Since tires and wheels were specific to a single vehicle platform, Ford would check to see if they needed to change the specified offset or not.

In the case where tires from different tire manufacturers could be applied to a given wheel, they both had to be checked. In the case where a tire could appear on several wheels, they all had to be checked. Needless to say, this occurred long before Job 1.

Posted by SwinningGG: "None of the above.

Wheels were produced using standard processes, which result in wheels which are/were imperfect. Each wheel would be measured as needed to identify if runout is within spec. If it isn't, the part is scrapped, and if it is, the part is marked accordingly (or not at all, if that's the manufacturer's method) to identify the location of highest runout.

Greg's linked Jaguar document talks about match mounting of tires - which happened 30 years ago and still happens today depending on manufacturer. That process says nothing about, and has nothing to do with, how the wheel is machined.

No one purposefully machined pilot bores off center."

I hear what you are saying, but it contradicts what both Greg and I have experienced. So I'm not inclined to believe you.

But it's possible that your experience is different than ours - particularly if that experience is recent and ours was quite some time ago.

So please help us understand. What is your background on the subject? How far back in time does your experience reach? It's quite possible we are looking at different parts of the preverbal elephant.

The lug centered wheels I'm personally aware of are from days long gone by.

UniLug wheels from the 1970s, but still made today.

Not all aftermarket wheels have oversize center bores.
I believe those modern aftermarket wheels with oversize center bores are intended to be used with "spacer rings" to specifically provide a hub centric mounting.
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CapriRacer said:

I hear what you are saying, but it contradicts what both Greg and I have experienced

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....no it doesn't.

You are conflating two very different scenarios - purposeful off-center machining of a wheel pilot bore, versus match-mounting tires to wheels while using the fact that machining perfect parts is not possible to some advantage in maximizing the roundness/balance of the final assembly.

These are not the same. Greg's linked Jaguar document says nothing about the center bore of the wheel being purposefully machined off center.

You're neglecting several factors that make what you're saying not make any sense:

1) Until relatively recently (early 90s or so), the overwhelming majority of wheels for road cars were not 'machined' at all - they were made from stamped steel centers welded to spun rims. These wheels were generally not all that round compared to the standard set by a modern CNC machined wheel. Figuring out where they were out-of-round was relatively simple. There were some cars being sold with machined wheels, but they were not the near-universal standard that they are today. Not even close.

2) The center bores on machined wheels provide some locating function, but by necessity they fits used are not sufficient to provide the type of precise location adjustment needed to correct for a tire that's out of round by a few thousandths of an inch. Hub-centric wheels need to be very easy to install by hand without being precisely aligned, they need to not freeze to the hub under a wide range of temperatures, and they need to handle being exposed to elements and corrosion also without freezing. As a result, the clearance between hub and bore is large and does not provide precise centering of the wheel.

3) All modern wheels, and most wheels going back to antiquity, are not 'hub centric' - the centering function is provided by the tapered seats of the fasteners. This is why the lug nut/bolt faces are tapered in the first place. In the case of a BMW that uses lug bolts, all the center bore does is make it so you don't have to hold the wheel up in the air while you fumble around to get the first lug bolt in. As soon as the first tapered fastener is tightened, the center bore is no longer doing anything. This is also why a lot of 'hub centric rings' for aftermarket wheels are made from plastic. They are only providing some centering function until the lugs are tightened - the lugs themselves center the wheel and clamp it to the hub flange.

I believe those modern aftermarket wheels with oversize center bores are intended to be used with "spacer rings" to specifically provide a hub centric mounting.

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The "close" fit hub-wheel and plastic spacers included with aftermarket wheels are DFMEA-driven, functionally they can be done without (and often are). The reason for them is bc folks changing flat tires often only jack a vehicle up high enough to remove a flat tire, not high enough to install a fully inflated spare. That leads to some jamming the spare on at an angle and using the lugs to pull the wheel onto the hub. Tire-ground contact and angle of the wheel can have a big impact on lug torque and has led to folks driving away with loose wheels. As a safety pokeyoke, the wheel/spacer-hub fit is controlled to encourage installing the wheel straight/flat onto the hub.

As mentioned modern light-duty wheels are lug-centric, relying on tapered lug nuts/bolts. Not sure when hub-centric wheels and flat hardware stopped being used on light-duty vehicles but its been a few decades since I've seen it.

My memories are very hazy on this. "My" alloy wheels were lug centric, so we didn't do it locally. But as I understood it from an NVH conference in Detroit, the process was that the tire manufacturer would estimate their average 1st order tire radial force variation (3rd order is also important) F, that spot was measured on every tire and marked. Every wheel centre hole was then finish bored off centre by a fixed amount related to F/(tire stiffness).

"were there different part numbers, with each part number having a slightly different runout dimension" On a typical production line you couldn't have multiple wheels of each style each with different sub part numbers and offsets, poke yoke would be a mess and there isn't physically room to store them all. I suppose one alternative would be to switch to offsite wheel and tire assembly, then it's just a sequencing problem. We did that a lot.

So, it was being discussed in the early 90s, tire radial force variation was a huge warranty cost, it is still a consideration today but I haven't done wheels or NVH for 25 years.

We switched from hub centric to lug centric some time (I think a long time) prior to 1990.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

SwinnyGG (Mechanical)

Good posts.

GregLockock said:

Every wheel centre hole was then finish bored off centre by a fixed amount related to F/(tire stiffness).

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Respectfully - I know you've been around the block - but I do not believe this. I suspect you are misremembering, for a multitude of reasons. Or that potentially this was a hair-brained scheme presented at some conference but never actually put to use in the real world.

The primary one is that I know to a certainty that the stamped steel wheel centers which were universal across almost all production models - the few exceptions being high-end performance models in the 60s and 70s which came with 'Mag' wheels - were not machined at all after stamping. The center bore of the stamped wheel center is as-drawn during the pressing of the wheel.

Secondly, every manufacturer used the exact same wheel across multiple models with different tires. As you've already stated, managing multiple part numbers that are cosmetically and functionally identical would be a nightmare, to the point of being a non-starter; using the same part number at the same tolerance would result in different performance at the assembly level for each set, which negates the whole point.

On top of that, machining the center bore off-center would require machining the lug holes off-center as well. The lug holes in these wheels were/are stamped. Moving them would yield oversize holes, holes with the tapers not centered on the stud centerline, and myriad other issues. This was not done.

I have not issue at all with match mounting - this is still done today- or the concept of measuring finished wheels and marking them for peaks in runout, or for using tire expected tolerances to set the acceptable tolerance window for wheel assemblies. No problem. All logical, all very easy to do in the production environment. None of that has anything to do with deliberate off-center machining of wheel features, which would create more problems than it would solve.