GTA IV: Installation of vehicle mods
Installing vehicle -mods:

1. If you haven't done yet, download SparkIV (Download) and a vehicle mod.

2. Start SparkIV and click on "Open". Then choose vehicles.img, which is located in pc/models/cdimages/.

3. Click "Import" and choose the WFT and WDT files of the downloaded vehicle mod to replace the old files with the new ones.

4. Click "Rebuild" and then "Save".

5. Maybe you have to replace some lines in carcols.dat and handling.dat which are located in common\data. More detailed information can be found in the readme.txt file of the car mod.

Video -Tutorial