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Re: [T3] Computing offset


Toby_E asked about calculating wheel offset.....

The calculating part is pretty easy.  The goal, from the
bearing's point of view, is to keep the centerline of the wheel
in the same position and let the width of the wheel increase both
inside and outside.  Therefore the offset should not change.  The
backspacing (measured from the inside wheel rim to the mounting
face) will change by half the difference in the widths.

The problems are two fold.  The first is that wheel manufacturers
only offer a limited choice of offsets unless you shell out the
bucks for custom billet or two piece wheels.  The other problem
is that you have now moved the inside edge of the tire and wheel
in about 3/4 ".  You will probably experience tire rubbing
problems.

If the goal was to keep the inside rim of the wheel in the same
realtive position with respect to the body, then you would let
the offset decrease by half of the difference.  All of the width
change to the outside.  So to go from our stock 114.3mm (4.5in)
wide rims with 43mm offset to a 152.4mm (6in) wide rim the offset
should decrease by y3¹mm) of the difference
152.4-114.3=38mm) in the rim widths.  Then new offset should be
24mm.

Unfortunately the same problems apply.  You will just be rubbing
the fender instead of the inner wheel well.

Don't have the answer to which wheel/tire combo is best, but I am
working on it......

John Jaranson
'71 FI Auto Fasty (I wonder how hard it would be to resculpt the
inner fender wells to handle those 245/40r17's........8^)  )

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