Correct diameter of centering hole in Mopar wheels?

[Ghoste]

Versus the diameter in some of the Ford ones?  (because some Ford wheels fit and some do not-at the back anyway)

[MaximRecoil]

The center holes in a set of stock stamped steel Mopar wheels I have here (and were on my car for a while; all fit perfectly on the hubs) measure 2-13/16" diameter. This agrees with what Google says too.

[Ghoste]

Thanks.

[dangina]

71.5mm
ford is 70.5mm

[MaximRecoil]

71.5mm
ford is 70.5mm

Both Ford and Chrysler wheels of this era were manufactured according to U.S. customary units, which means the correct measurements are:

Chrysler: 2-13/16"
Ford: 2-3/4" (for the ones with a center hole that almost fits on a Chrysler, but not quite)

For the folks who are fond of the French units, that translates to:

Chrysler: 71.4375 mm
Ford: 69.85 mm

[dangina]

For the fords i mean mustangs of that era - my spindles are a mustang hub and it's 70.5mm

[MaximRecoil]

For the fords i mean mustangs of that era - my spindles are a mustang hub and it's 70.5mm

Ford was using the metric system in the '60s? That's odd.

[bill440rt]

A measurement is a measurement no matter which method is used.

[MaximRecoil]

A measurement is a measurement no matter which method is used.

It is still odd that Ford would use the metric system for anything in the '60s. Nothing on my '69 Dodge is metric that I've come across yet.

70.5mm doesn't translate to any standard 1/16"-increment U.S. customary unit, nor even a 1/32"- or 1/64"-increment unit (it falls somewhere between 2-3/4" and 2-13/16", i.e., about 2-199/256", or more precisely, 2-775591/1000000"), which means they intentionally specified a metric dimension for that, and an American car company doing that in the '60s is bizarre.

[ws23rt]

The hub dia. on mopars that I have dealt with are different on the front vs the back. --The front is smaller than the back--  This leads me to think that the intent for wheel alignment to shaft center on the front relies more on the lugs than on the rear.

This may explain why an oversize or worn wheel from ford will fit with greater ease on the front vs the back.

No matter which unit of measure one uses the diameters are what they are. Inch vs metric are two languages that speak the same thing. If one has a metric measuring tool that is the unit of measure for the discussion. The number of decimal points of accuracy is I think the issue here. If it were not than the question would be about how close or accurate are the measurements.

When someone uses fractions of in. (for example) to describe a measurement they have taken I take that to be +/ 1/32.  In metric I would take it to mean +/- 1/2mm. Had dangina said his hubs were (for example)70.479mm than that would justify dragging this out further.

[MaximRecoil]

No matter which unit of measure one uses the diameters are what they are. Inch vs metric are two languages that speak the same thing. If one has a metric measuring tool that is the unit of measure for the discussion. The number of decimal points of accuracy is I think the issue here. If it were not than the question would be about how close or accurate are the measurements.

When someone uses fractions of in. (for example) to describe a measurement they have taken I take that to be +/ 1/32.  In metric I would take it to mean +/- 1/2mm. Had dangina said his hubs were (for example)70.479mm than that would justify dragging this out further.

I'm not just going by what Dangina said; I've looked at other sources and it seems that the actual measurement is indeed 70.5mm. For example, these wheel spacers which fit '60s Mustangs have a 70.5mm center bore, which means Ford was using the metric system to some extent in the '60s, and I find that bizarre.

When a metric measurement doesn't translate to a relevant U.S. customary unit measurement (which is usually in 1/16" increments on a car), that means the measurement was intentionally specified in the metric system by the manufacturer. Of course, that happens all the time these days on American and "American" cars, but until this thread, I never knew it happened with any American cars from the '60s.

[John_Kunkel]

Or the metric dimensions are just "rounded off" to the closest even number.

[bill440rt]

As occurred all to often with cubic inch engine displacements. (And still do.)

[MaximRecoil]

Or the metric dimensions are just "rounded off" to the closest even number.

No. 70.5mm is somewhere between 2-3/4" (69.85mm, which would be rounded to either 69.9mm or 70mm) and 2-13/16" (71.4375mm, which would be rounded to 71.44mm, or 71.4mm, or 71.5mm if rounding to the nearest half-mm).

As I said, 70.5mm doesn't translate to any relevant U.S. customary unit, and neither does any metric measurement that's within a half-mm of 70.5mm. That means that Ford intentionally specified a 70.5mm center bore for their wheels in the 1960s, i.e., it is obviously not a case where they specified a U.S. customary unit measurement that just happened to be close enough to 70.5mm to call it that later on (unless they specified e.g., 2-199/256", which would be just as bizarre as specifying a metric measurement).

Maybe they did it so that the only proper-fitting OEM wheels were made by them, knowing that no other American car company in the '60s was likely to do something so strange (for the time) as to have a metric-size center bore.

[Ghoste]

Very odd even more when you consider how unlikely it was that any European Ford product of that time (or since) required a center hole that large.  (as a once in the distant past Cortina owner)

[JB400]

All this bickering of fractions of an inch and millimeters, but no mention of tenths of an inch?

[Ghoste]

It kind of spun off into an interesting discussion of automotive history.  Trivial but still interesting in a way, Maxim raises a very good question.  Not a what is the meaning of life question by any stretch but mildly interesting to students of auto history.

[MaximRecoil]

All this bickering of fractions of an inch and millimeters, but no mention of tenths of an inch?

Tenths of an inch are only used to decimalize a fraction. British imperial and U.S. customary units were never designed around base-10; that's a metric thing. Standard wrenches, sockets, etc., are not sized in tenths of an inch; they are in 1/16" increments, or multiples thereof, such as 1/32" (rare) and 1/64" (even more rare) increments. Rulers and other measuring devices are the same way.

[ws23rt]

Or the metric dimensions are just "rounded off" to the closest even number.

No. 70.5mm is somewhere between 2-3/4" (69.85mm, which would be rounded to either 69.9mm or 70mm) and 2-13/16" (71.4375mm, which would be rounded to 71.44mm, or 71.4mm, or 71.5mm if rounding to the nearest half-mm).

As I said, 70.5mm doesn't translate to any relevant U.S. customary unit, and neither does any metric measurement that's within a half-mm of 70.5mm. That means that Ford intentionally specified a 70.5mm center bore for their wheels in the 1960s, i.e., it is obviously not a case where they specified a U.S. customary unit measurement that just happened to be close enough to 70.5mm to call it that later on (unless they specified e.g., 2-199/256", which would be just as bizarre as specifying a metric measurement).

Maybe they did it so that the only proper-fitting OEM wheels were made by them, knowing that no other American car company in the '60s was likely to do something so strange (for the time) as to have a metric-size center bore.

This is interesting that you have a definitive grasp on how dimensions are rounded off. And in this case you chose to use a second place decimal as the place to round from.  Some rounding is done from a first place decimal. Or even next whole number.

The reasons one rounds off dimensions vary and in nearly all cases they are not dimensions intended to fabricate from. 

Without a fabrication print of the parts and the hole size tolerance to refer to, this is just another exercise in picking nits and wondering.

When it comes down to it all advertised dimensions are false. What matters to the buyer is does it fit?

[MaximRecoil]

This is interesting that you have a definitive grasp on how dimensions are rounded off. And in this case you chose to use a second place decimal as the place to round from.  Some rounding is done from a first place decimal. Or even next whole number.

The reasons one rounds off dimensions vary and in nearly all cases they are not dimensions intended to fabricate from.  

Without a fabrication print of the parts and the hole size tolerance to refer to, this is just another exercise in picking nits and wondering.

When it comes down to it all advertised dimensions are false. What matters to the buyer is does it fit?

As usual, you are posting from way out in left field. Once again:

As I said, 70.5mm doesn't translate to any relevant U.S. customary unit, and neither does any metric measurement that's within a half-mm of 70.5mm.

If something on a car measures 70.5mm, the manufacturer decided to make it 70.5mm. This isn't a case of something measuring e.g. 19mm (~3/4") or 27mm (~1-1/16"); 70.5mm doesn't convert to any inch fraction that a car manufacturer would likely specify for a wheel's center bore, and neither does 70mm or 71mm, or anything in between.

I don't even know what it is that you are trying to say overall (because I don't speak "Left Field™"), but I do know that it is entirely irrelevant to anything I've said.

[Ghoste]

And then the train went crash.

[ws23rt]

Let's go back to the top

The center hole in wheels are generally not intended to center the wheel. The bolt circle and lug nuts do that.

Their are many manufactures of wheels and it is common that the center holes be of a size that allows for fitment to a range of hub sizes. The bolt circle diameters are much more universal than the hub diameters and do the centering. I'm sure their are exceptions and some folks use spacer rings as needed for greater security.

A manufacturer that sells a wheel intended for a ford could very well fit a mopar if the center hole is big enough so they make them that way. The size of hole they chose is arbitrary. Their are many aftermarket wheel manufacturers and for some of them to advertise dimensions in metric is no surprise.

It would be interesting to know what size holes for the wheels ford used as original equipment. It might be a round metric number

[JB400]

All this bickering of fractions of an inch and millimeters, but no mention of tenths of an inch?

Tenths of an inch are only used to decimalize a fraction. British imperial and U.S. customary units were never designed around base-10; that's a metric thing. Standard wrenches, sockets, etc., are not sized in tenths of an inch; they are in 1/16" increments, or multiples thereof, such as 1/32" (rare) and 1/64" (even more rare) increments. Rulers and other measuring devices are the same way.

Obviously, you know very little about machinist measurements, which is measurements used by engine builders and everyone else that work with metal.  They use tenths of an inch because it can easily be converted to metric, thus the same set of measurements can be used worldwide and the parts manufactured can be interchanged, no matter who made them.

Going by Dangina's measurements:  Chryslers' 71.5 mm =2.815 in.  Fords' 70.5 mm = 2.776 inches.  Put into this format, I hope you realize why Ford wheels "almost" fit on a Chrysler, but not quite.

As for why wrenches are put into fractions, it makes for quicker identification of the wrenches.  Otherwise, looking for wrenches would be like looking for drill bits.

If you wish to use your fractions, I would suggest you stick to building cabinets.

[MaximRecoil]

Let's go back to the top

The center hole in wheels are generally not intended to center the wheel. The bolt circle and lug nuts do that.

False. Practically all OEM wheels are hub-centric when installed on the type of vehicle they originally came on. Aftermarket wheels are usually lug-centric, or more specifically, they usually end up being lug-centric in application, because the center bore on many or most aftermarket wheels is intended to clear a variety of hub sizes, and in such cases, it is unlikely that the hole will ever exactly match up to the hub size on any given car.

Hub-centric and lug-centric are not inherent properties of the wheel itself, but rather, it is a property of the application, i.e., a Mopar wheel is hub-centric on a Mopar, but it would be lug-centric if you installed it on a Ford.

Their are many manufactures of wheels and it is common that the center holes be of a size that allows for fitment to a range of hub sizes. The bolt circle diameters are much more universal than the hub diameters and do the centering. I'm sure their are exceptions and some folks use spacer rings as needed for greater security.

A manufacturer that sells a wheel intended for a ford could very well fit a mopar if the center hole is big enough so they make them that way. The size of hole they chose is arbitrary. Their are many aftermarket wheel manufacturers and for some of them to advertise dimensions in metric is no surprise.

See above, and also, this particular line of the discussion is about OEM Ford wheels; not aftermarket wheels that will fit on a Ford. That should be obvious based on the number of times I've mentioned out how bizarre it is that Ford chose a 70.5mm center bore for some of their wheels in the 1960s.

It would be interesting to know what size holes for the wheels ford used as original equipment. It might be a round metric number

It has already been pretty well established in this thread that it is 70.5mm for certain '60s Mustangs (for example, I've already linked to those wheel spacers with a 70.5mm center bore, which are intended to be hub-centric, and fit a variety of Mustangs starting with its first model year in the mid-'60s, and Dangina has given his measurement), which is the entire basis for this line of the discussion in the first place.

The reason for your confusion is that you haven't read this thread properly and you have a fundamental misconception with regard to hub-centric vs. lug-centric.

[MaximRecoil]

Obviously, you know very little about machinist measurements, which is measurements used by engine builders and everyone else that work with metal.

This is a non sequitur (because the idea that "Obviously, [ I ] know very little about machinist measurements") doesn't logically follow from anything in this thread), and as such, consider it dismissed.

They use tenths of an inch because it can easily be converted to metric, thus the same set of measurements can be used worldwide and the parts manufactured can be interchanged, no matter who made them.

We are talking about 1960s American car manufacturers, plus we are talking about a center bore in a wheel which was usually stamped steel, not machined. Also, tenths of an inch are no easier to convert to metric than sixteenths of an inch or anything else. As I said, tenths of an inch are for decimalization, which makes calculations easier, particularly when using a calculator/computer which doesn't typically accept direct input of fractions.

And in the manufacturing process, extremely tiny increments, whether in multiples of 16 or base-10, are usually only used for tolerances, not for the intended nominal dimensions of a part. For example, a part might have an intended nominal diameter of 3/4" or some other standard fraction of an inch, but with a lathe tolerance of .001". Something like .776" as an intended nominal diameter of a part would be very unlikely for a company using U.S. customary units

Going by Dangina's measurements:  Chryslers' 71.5 mm =2.815 in.  Fords' 70.5 mm = 2.776 inches.

Chrysler = 2-13/16"; which is close to 71.5mm. As far as I know there is no reason to suspect that Chrysler specified that their wheels in the 1960s be manufactured with a 71.5mm center bore rather than a 2-13/16" center bore. The situation is different with Ford though, because as I've said many times now, 70.5" doesn't convert to any standard inch fraction, nor does it even sort of convert to any standard inch fraction.

Put into this format, I hope you realize why Ford wheels "almost" fit on a Chrysler, but not quite.

Is that a joke? I'm well aware that 70.5mm is smaller than 2-13/16", and you would already know that had you read the thread properly before posting. I've said that 70.5mm is somewhere between 2-3/4" and 2-13/16" at least twice already, and I've even given precise conversions for all of those dimensions.

As for why wrenches are put into fractions, it makes for quicker identification of the wrenches.

I didn't say merely that they were put into fractions, I said that they are put into 1/16" increments and multiples thereof, because that's what the U.S. customary and British imperial system has always been based on. That's why you won't find a size 7/10" wrench in your toolbox.

If you wish to use your fractions, I would suggest you stick to building cabinets.

It looks like we've got another deep left-fielder on board. JB400, meet Ws23rt. Ws23rt, meet JB400.

By the way (and not that it is relevant, because I said absolutely nothing at all about "wishing to use [my] fractions"; that's just something you pulled out of thin air out there in deep left field), decimalized numbers are fractions too. For example, .776 is just an alternate way of writing 776/1000 (97/125).