Swedespeed Forums - Wheel Offset Tutorial
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from the above link:
" The offset of a wheel is the difference between the wheel's centerline or plane and its mounting plane. Offset is the same as ET (a German abbrev.)
That mounting plane is sometimes defined using backspacing, which can be equated to ET.
Backspacing – (wheel width ÷ 2) = offset
FWD and AWD cars use a positive ET, the ET number is mm, millimeters
The R has a factory ET46 whereas other modern Volvos are 35 or 38.
A smaller ET moves the wheels outboard with the following effects:
- wider track (unless you use a narrow tire)
- altered suspension and steering geometry
- chance for inner fender rub
- increased caliper clearance
If you are using a narrower rim and/or tire, this may be a good thing
A larger ET moves the wheels inboard with the following effects:
- less track (unless you use a wide tire)
- altered suspension and steering geometry
- chance for inner wheel well rub
- less caliper clearance (unless wheel spokes give more)
Not many times to use a larger ET on an R
Adding a wheel spacer to an existing wheel has the same effect as a wheel with a smaller ET. "
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