I would suggest to make the following steps as the first meeting to modding:
1. import original vehicle (custom) wheel - the one you would like to be replaced. Toggle "L0" on "Structure" panel, switch object to vertices mode (press '1', hover and click the wheel in viewport), pick Modify\Move tool, hover any wheel vertex and move it away to create a "spike". then export this scene into the file named the same way as original; add modded file into the game via OpenIV and check in game. You should see a modded (spike) wheel in game.
2. another test, but it is very alike: Import original wheel, toggle L0 to see hi-res version. Now create a small box using "Cube" tool in primitives toolbox. a new object will be created. Select it by hovering and pressing Shift+S. (Tip: Shift+A to select all, Shift+D to deselect all; Shift+S to select/deselect hovered object). Now open materials browser by pressing green material sphere in main toolbox. Locate a material associated with original rim/disk. pick it, then drag&drop onto left side of materials browser onto a "Scene Selection" branch (it will probably show there "Scene Selection -> Default material" --> changing to --> "Scene Selection -> some_wheel_material_name"). You have assigned original wheel material onto a box. Now attach this box to original wheel using Modify\Attach tool (click on box in viewport, then click on wheel). wheel + box will become single object. Export, put into mod, test in game.
3. very alike to the test before, but this time the box object is not attached to the wheel, but will replace it. Use this video guide to find out how to compose and set up "Compound" objects: (you will need to use "Dismiss" button first, to disassemble original compound object first).https://www.youtube.com/watch?v=_x07ZDfq0BA
Now, when you succeed in three modding lessons above, you can mover further and replace wheel with the custom model you have.
Note: the material you assign onto a wheel model must have "Adapt: vehicle_tire" specified on material tile in materials browser. this is the only acceptable material adaptation to use on a wheel in game.