I can't tell, from what little you've told so far, but the car tute worked for me. One thing I discovered is that you have to place vertices, as his tute describes, to identify the
ground contact points. Did you do that?
Also, you must have a config.cpp file to go with this model. He offers one for download. Did you include that in the folder with the model, before you compressed to a .PBO file?
I'm discovering that the car's .CPP file can't just be dropped in for my tank; I'm picking thru a T72 model [from the downloadable demo models at
http://www.geocities.com/kungtotte/], and trying to make parts of my model match parts of that one, with the same Czech names for the same selections. It's exhausting and boring. I think I'm going to go begging for a proper tank's .CPP file [I haven't found one yet], because I don't have one and I don't know enough to make one from scratch.
I'm a fellow newbie, so these suggestions might be premature. Just trying to help.