Well, like apex mentioned...it doesnt hurt to have it. But unless you can get some seat time/practice you'll probably never pass the road test. Granted it just common sense, but you still have to know how to drive it.
I took my CDL test on my own, read the book for a few months, got pretty confident, then took written. I waited about a month and took driving test. Now, I'd pulled my 40ft race trailer around for 7 yrs, and had my B model Mack for about 9 months playing with it. I rented a truck(from the test station) and passed the test pretty easily. The rental truck was a little 4600 International with synchro'd 5 spd...real easy to drive with 40ft flat bed.
Not all test places have rentals, if you can't get your hands on a truck then you'll be out of luck. Ryder won't rent a big truck to a non CDL driver, so that's out.
Good luck.