This is a semi-long treatise on automotive wheel manufacturing, for
those who would like to know. If you are not interested, stop here.
Bennett Cullen-R51465 wrote:
------, on a front hub and measured the run-out on the front and edge of
the rim with a dial indicator. Out of the five wheels that I had
machined, the worst case "wobble" was just under 0.030". That one ended
up being the spare tire wheel. The remaining four were on the order of
0.015" "wobble" which has been very acceptable for my driving "sensory
feel". I suspect that the rubber portion of the wheel has much more
variation, especially after a few thousand miles of stop 'n go.
> Cullen in Tempe (B9472658)
Tigers,
I imagine this is lateral wobble, but am not sure. It could be radial
(circumferential) centering. This is a whole new kettle of fish. Radial
eccentricity.
Does anyone know how wheels are made? It is a fascinating process.
Having been in this business, let me tell you of my experiences.
When I was at a high level, with a prestigious metal forming machinery
company in Illinois, we were the leading supplier of fully automated
automobile and bicycle (Schwinn) wheel manufacturing lines.
In the case of our Tiger motor benefactor, Ford, they purchased our
finest automated production line. This line of machinery, and transfer
equipment, was fed with very large rolls of strip steel from the mill.
After this roll was installed, everything else was automatic. The roll
was unwound through a cutter for length (depending on wheel size, was
transferred to an automatic flash butt welder to create a hoop, the
excess weld was automatically trimmed off to a flat surface, and the
hoop was transported once again to a series of roll formers to make the
rim. There were 4 to 5 stations for progressively forming the wheel rim
cross section. Each operation was on a specialized piece of equipment,
and was automatically moved to the next station. Each station was
connected by automated material transfer, loading, and unloading
equipment. A human hand was only present to set the line up for the
wheel it was to produce, which included the whole line from 13 to 16
inch wheels. Operation was totally automatic, and humans were kept away
(for their own safety, as this was a very fast operation of moving,
spinning metal.
The hub was die pressed in a separate line and joined with the rim in a welder.
This was the most sophisticated production line in the world for making
wheels, and cranked them out at over 1,000 wheels per hour.
Now that you have a feel for the top-end in wheel production, let me
tell you about how this relates to the concentricity issue. At the end
of this process, the wheels were painted and shipped to the assembly
plants for tires and mounting. Except for the wheels for the Lincoln
(top of Ford's line). These wheels, and ONLY these wheels were sent on
to one more automated station. The wheel was placed in a hydraulic
radial press with eight circumferential dies shaped to the final inner
wheel contour, but withdrawn radially for wheel entry. The wheel was
centered on a precision hub and bolt hole fixture and the wheel radial
dies were hydraulically extended until they met at precisely the correct
diameter,
This performed a number of operations, simultaneously. Firstly, the
wheel was absolutely centered with the hub/bolt hole fixture in the
radial and vertical direction (although the wheel was actually
horizontal in the huge press, it didn't care). The rim was forced to
have the offset exactly as designed by purposely yielding the metal so
the spring-back position was exact. Lastly, and most importantly, the
wheel rim was made round to rigid specifications by the same precision
tooling / metal yielding method.
The end result was as centered and planar laterally as possible (and way
better than standard), as well as exactly round and centered radially.
This was probably the only wheel on a production car that was actually
flat and round no matter which way you measured your run-out. And only
if you bought a Lincoln. (Yes, GM was a customer as well).
Bearing this in mind (and having seen what a chore wire wheel alignment
is), you can be assured you are running on egg-shaped, laterally bent
wheels, otherwise. And they are probably good enough. (unless you are
putting on racing loads - and we don't do that, right?)
The LAST observation is that "Mag" (both aluminum and magnesium) wheels
are cast, and come out of the molds in a raw state. They are machined to
size, both laterally and radially, around whatever mounting method is
used, be it hub centric, or attach bolt centric. Inherently, the
machining process is more accurate than the best metal forming
methodology. I would be willing to state that a reputable manufacturer
is turning out a cast wheel (or forged if you have a Porsche) to a more
accurate roundness and concentricity than the best sheet metal wheel
that can be made. There are, of course, small, cheap shops. Some use the
larger non-hub centers for locating bolt holes made after manufacture of
finished "blanks", but these are made on precision milling/drilling equipment.
This does NOT mean that all "Mag" wheel manufacturers are equally good,
nor does it mean that an individual wheel was not mal-manufactured due
to machining chips on the mounting surfaces (cheap shop), or use bending
through striking objects such as curbs.
Bottom line? You are probably better off with a major manufacturers
"Mag" wheel than the best steel wheel, regardless of mounting method.
Handling, or use damage and manufacturing errors can make any wheel bad,
so radial and lateral measurement is in order in any event.
Steve (who actually made more than Rockets)
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____________________________
Steve Laifman
Editor
<http://www.TigersUnited.com>
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