My Dad and I have widened a number of steel wheels at home, most notably converting 15x7 truck sport full face wheels (Motorwheel) to 15x8; and converting 15x8 Corvette rally wheels to 15x10 or 15x12 configurations.
We widen the wheels by preserving the front half (thereby keeping the dimensional integrity between the wheel spider and the front face of the rim) and by cutting the back portion off the wheel.
A new back portion, from a different wheel and with an additional 2", would then be fixtured to the front face/spider, using this spacer as a checking fixture, for a 10" wheel. To create a 12" wheel the front face would be cut and replaced after that rear portion was secured.
This is the spacer, used as a fixture for controlling the overall width, made from a piece of black pipe.
The length of the spacer corresponds to the final wheel width. These are placed in three or four locations around the wheel and are secured with small screws in the end.
A small plate was affixed in four locations, allowing for minute adjustments of the donor portion. Once the radial and lateral runout are within spec then the two halves can be welded together.
Here is a finished sample, a 10" Corvette rally with the front spacing preserved and the 2" added to the rear.
