I don't know if there is a "standard" method of specifying offset for
wire wheels, but it's easy enough to measure them for
comparison. With any wheel you find center of the rim by measuring
the width and divide by 2. For a wire you can find center of the hub
the same way, measure width between the taper mounts and divide by
two. Also measure discance from one side of the rim to one end of
the hub, and you can then calculate offset from center of rim to
center of hub. Alternately you could use the distance from rim
center to hub inboard end as the offset dimension (for comparison
between wire wheels).
WW rear axle is 7/8" shorter each side than the DW axle (at face of
brake drums). Offset of a stock 4" wide steel wheel for MGA is
1-3/8" (35mm). MGB wheels might be slightly different, maybe, but I
think not much different, certainly not as low as the 22mm often
noted in custom wheel sales information. The WW hub does not touch
the brake drum but sits at least 1/8" to 1/4" away from it. Mating
cone surfaces are even farther out. I don't have any WW parts or
hubs in hand to mearsure, but here's a rough guess for example. If
the inner cone is 3/4" away from the brake drum, and the cones are 4"
apart, then the hub center is 2-3/4" from the face of the
drum. Assuming same track width for DW and WW cars, this puts center
of the WW hub 1/2" farther outboard than the bolt-up surface for DW
cars. This would make WW offset 1-7/8" (48mm), measured to center of
the hub between cones. Anyone with WW parts in hand may feel free to
fil in the real dimensions.
When considering wider wheels for a WW car, you should add width
equally to inboard and outboard sides of the rim to maintain original
track width. If you are looking only at the inboard end of the hub,
then when going to wider rims you should add half of the increase of
rim width to the "backset" dimension (distance from inboard side of
rim to inboard end of hub).
Barney
At 02:02 PM 1/27/2010 +0000, Paul Hunt wrote:
>Stud wheels are easy - you simply measure the distance from the
>centre-line of the wheel to the face of the wheel hub that bolts up
>to the axle hub, which is usually flat. But what about wire
>wheels? It is measured to the back of the wheel hub or at the inner
>taper? And if at the inner taper is it the wider edge? The
>narrower edge? Or between the two?
>
>MGB wheel offset is usually given as '22mm approx', but doesn't it
>vary with wheel width in order to keep the wheel centralised in the
>well? 4", 4.5" and 5" widths were used at various times, my 5"
>Rostyles measure 26.8mm, and my 4.5" wires 20.45mm (to the middle of
>the taper). Shouldn't wire wheel offset be significantly less than
>steel or alloy? Isn't that why wire wheel axles are 1.75" (banjo)
>or 1.5" (Salisbury) narrower than stud axles?
>....
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