18 or 20" wheels?

[86gmcstepper]

Anyone ever heard of an 18" by 12" wheel for a square body. i have a 86 gmc stepside and the guy before me did a "tub" to the inner fenderwells. So i can fit 12" wheels no issues. Currently running 18x10 ridlers with 295s on back and jyst want to put the biggest tires on backside i can since i have the space.
Thanks

 

[jimmy78]

20's Detroit Rally's on this C10

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18 on the front and 20 on the rear on this square

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Or these 20" Detroit Mack wheels in white

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What’s the offset on a set of 20’s looking at the dtown smoothies for a 4/6 belltech drop on a 78 jimmy