You can install car mods in GTA San Andreas. Follow the simple steps below
Download any mod for car, bike, bicycle. There are several available
http://www.gtainside.com/en/news.php
http://www.gtagarage.com/mods/index.php
Download SAMI (San Andreas Mod Installer) for beginners.
Free download GTA SAMI
Open SAMI and click on install mod.
Select the directory of your Grand Theft Auto San Andreas folder.
Select the mod location.
It will display car lines click on next then type the name of the car it will be on the top just type the name, and click on install the mod.
Note
If you are installing the mods with SAMI, you can also use SAMI to remove them.
Create backups of your data if you are replacing data.