Thanks! You're right, the current parts system does not allow for recursive parts (eg self-referencing / infinite recursion). The way this mod works is actually slight-of-hand. I wrote a Lua script for automatically modifying parts. For any given wheel/tire slot that it works with Spaced Out generates one or more evil twin slots. For example, if the slot is 'wheel_abc' then the mod will generate a slot called 'torsion_wheel_abc_offset+60' for the 60mm offset parts. It also creates modified copies of all the parts that fit into this slot. If you look at your log or console you should see some output related to that process. This mod was created 3 years ago, before the recent jbeam variable upgrades (eg math and conditional expressions). I'll likely be making some changes to accommodate the new jbeam variable capabilities. :-| Given the above, it's definitely not stackable. It's possible that 'spacer skins' might one day give the appearance of stacked spacers (as well as colored / anodized aluminum spacers).