I have a 2002 stock S-10 and I would like to put 20s on it but i dont know how big I can go without it rubbing, and I dont really dont want to put the fenderwells out...

http://www.s10forum.com/forum/showthread.php?t=49477
This is a rim and tire fitting chart. should answer your question.

Thanks a lot, that really helped me out...now if I could just convince my dad that they wont cause problems, then maybe I'll soon be rollin' on dubs

Puts some airbags on it. That way you can drop it and raise it anytime you want. Check out that web site I gave you. It has tons of info on it. Just do a search for what ever question you need answered.