Track has to do with the measurement from tire center to tire center, not
from hub center to hub center.
I.e. 5-inch-wide wheels will measure track narrower than wheels 6 inches
wide, even on the same hubs.
But it is arguably difficult to measure precisely the center of the wheel --
especially when measurements a tenth (or less) off make a critical
difference in legal or not. So the inside/outside measurement is authorized.
Inside/outside sounds confusing. Really it is quite accurate. Think of it
this way -- looking at the car from the rear, measure from the right side of
the right wheel to the right side of the left wheel. That should be the same
as measuring from the center of one wheel to the center of the other.
Right side of the right wheel will be the outside. Right side of the left
wheel will be the inside. It gives you a very precise measure measurement
from a hard surface. Further, measuring at the hub centerline eliminates the
variables of camber. The usual tool is not a tape measure, but a sliding
device that looks something like [___[ where the open ends are placed
against the wheel and the bar between shows the measurement.
Whatever offset you may have will affect track. The inside/outside
measurement takes that into account also. I'm not sure if zero offset moves
the wheels inboard or outboard from the stock 2.75" offset. If it moves the
wheels outboard from stock, the resultant track change will be wider.
The whole point is to specify, and limit, where the tires sit on the ground.
That can vary a whole lot from where the brake drums and hubs are.
--Rocky Entriken
----- Original Message -----
From: <WEmery7451@aol.com>
To: <fot@autox.team.net>
Sent: Thursday, December 04, 2003 4:26 PM
Subject: Track Measurement Interpretations
> Dear FOTers,
>
> I am looking for some opinions on track measurements. The GCR describes
> Track as follows:
>
> "Track is the distance between the centerlines of the wheels as raced,
> without the driver, measured at a horizontal plane through the wheel hub
centerline."
>
> "Alternately, it may be measured from the inside of one wheel at the hub
> centerline height to the outside of the other wheel, then conversely from
the
> outside of the first wheel at hub centerline to the inside of the second
wheel."
> This section goes on to talk about toe-in corrections, etc.
>
> The TR-3 and TR-4 are presently allowed the front and rear track width of
53
> inches and 52.5 inches, respectively. Recently, I found three different
> racers who were using zero offset wheel rims on their Triumphs, and was
considering
> ordering a set for myself. The stock TR-3 wheel rims have a 2.75 inch
> offset.
>
> The few times in the past when I saw cars being checked for track after a
> race, it appeared that the measurements were being taken from the inside
of one
> wheel to the outside of the other wheel. Is it now acceptable and legal
to
> have zero offset rims made and say that the measurements are to be taken
at the
> rear brake drum surfaces and the front hub surfaces?
>
> After taking some track measurements myself, I would comply if the track
> measurements were taken at the drum and hub surfaces. If someone imposed
the
> alternate method of measuring from inside to outside of the tires, I would
not
> comply.
>
> Any opinions will be appreciated.
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