Ok thank u all for the advice. Think I got enough information regarding the tires. The next thing I'm planning to do is fix the spare tire on the back of the back body. I've seen many cases from the internet but still haven't got a right idea. The problem is that I didn't plan the structure of the extended part to hold the spare tire from the very beginning.
Have u got any experience regarding this matter (mean fixing the tire on the extended part)
Mongol