To figure out why the offset is different, you need to look at the OD of the 18" and 20" setup. If they are the same OD the offset would be the same for both. But if the OD is different, the change in offset will help maintain the desired scrub radius.
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2018 Hyper Blue Metallic 2SS 1LE with Nav, PDR, and track alignment
1:34.20 Willow Springs Big Track
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