Most 3D apps that can export (not "save" or "save as") as a 3DS file type have a good chance they can be used for TM 3D vehicle creation.
IMPORTANT. Before you spend days, months, years, and eons melting your brain with a very top flight 3D (Lightwave, Maya, 3D Studio Max, Cinema 4D etc.) application, it's best to do a test first.
1. Download one of the standard environment vehicles that a TM-Carpark professional has provided here :
http://www.trackmania-carpark.com/forum ... =14&t=6601
2. Import one of the 3D vehicle models into your chosen 3D application.
3. Delete all the other 3D parts except the main body (that'll take you a few minutes) as you're trying to keep it as simple and trouble free as possible at this point.
4. Make sure that 3D part is named "sBody". It's name and case are vital and must be exact, as SBODY, Sbody, etc. are not sBody.
5. Export the file as a 3DS file type, and name it.
Use the TM launcher > Help > Custom Data > Car Geometry > browse to the 3DS file and "open".
Now you'll have a GBX file in the same folder as the exported test 3DS file. Click and check the GBX's file size. If it is approximately the size of the 3DS file it converted from (it will be different, but it must be a reasonable file size), you have an application that exports 3DS files that are TM friendly and you can use it as you see fit. However, if you end up with a GBX file which is a file size less than 1 Kilobyte you have an application that exports 3DS files that aren't TM friendly. So far Blender and Anim8tor are two apps that do not
easily export 3DS file that TM can use. Another expert has created a custom Blender script that may allow it to be used though. Find more details and a guide to Blender here :