[DeTomaso] Wheel offset (ET)

[michael@michaelshortt.com]

Here's what I found.

Michael Shortt

he offset of a vehicle's wheel is the distance between the centerline
of the wheel and the plane of the hub-mounting surface of the wheel.
It can thus be either positive or negative, and is typically measured
in millimeters. Offset has a significant effect on many elements of a
vehicle's suspension, including suspension geometry, clearance between
the tire and suspension elements, the scrub radius of the steering
system, and visually, the width of the wheel faces relative to the
car's bodywork.
Zero Offset - The plane of the hub mounting surface is even with the
centerline of the wheel.
Positive Offset - The plane of the hub mounting surface is shifted
from the centerline toward the front or outside of the wheel. Positive
offset wheels are generally found on front wheel drive cars and newer
rear drive cars.
Negative Offset - The plane of the hub mounting surface is toward the
back or brake side of the wheel's centerline.
"Deep dish" wheels typically have negative offset or a very low positive offset.
To maintain handling characteristics and avoid undue loads on bushings
and ball joints, the car manufacturer's original offset should be
maintained when choosing new wheels unless there are overriding
clearance issues.
Wheels are usually stamped with their offset using the German prefix
"ET", meaning "Einpresstiefe" or, literally, "press depth". An example
would be "ET45" for a 45mm offset.
[edit]Calculating the offset of a wheel

First, measure the overall width of the wheel (remember, just because
a wheel is 18x7.5, does not mean that the OVERALL width is 7.5”. It
means that the measurement between the outboard flange and the inboard
flange is 7.5”). Next, divide that width of the wheel by two; this
will give you the centerline of the wheel.
Overall width/2 = Centerline
After determining the centerline, measure from the hub-mounting
surface of the hub to the edge of the inboard flange (if the wheel
were laying flat on the ground – face up – your measurement would be
from the ground to the hub-mounting surface). This is your back
spacing.
Back spacing - Centerline = Offset


On Wed, Aug 1, 2012 at 11:33 AM, Bjoern Flesland <bflesland at gmail.com> wrote:
> I am trying to determine the offset (ET) of two wheels and need some advise:
>
> One wheel measure 184 mm from the mounting face/flange to the inner rim edge.
> Wheel width is 228 mm.
>
> The other measure 216 mm from the mounting face/flange to the inner rim edge.
> Wheel width is 330 mm.
>
> Appreciate your help. Thanks!
> Cheers Bjoern
>
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Michael L. Shortt
Savannah, Georgia
www.michaelshortt.com
michael at michaelshortt.com
912-232-9390


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