Clueless: Tire info

Hi ppl, I have a few questions about buying tires. I drive a '04 black sedan w/ the stock 17" rims, and I want to buy new shoes for them. Now, looking at my current crap set of Bridgestone Turanza EL42's, it says that the size is a 215/55R17. Now, if I were to buy new tires, do i have to absolutely get this exact size in order to fit the stock rims?? Do the 17" stock rims only fit 215 size tires? can i go 225? Does it matter whether i get 55's, 50's or 45's (from what I know, that is the height of the sidewall, so maybe i should go less than 55 haha)?

Okay, so let's say i buy 215/55R17's. will any tire with that size fit the rim or are there other specific measurements that I need to know? Sorry for the annoying questions, but I just really want to clarify...

Thanks!!

Acemanic

I just got a set of 235-45-17's they feel and handle great, they are about an inch smaller in diameter than the stockers so my Speedo is now about 4% Fast. At the same time gearing is a bit lower so it is a little quicker off the line. The car sits a 1/2 inch lower and that suits me just fine but idealy you'll want to match the diameter a closely as possible.

The tire size works out like this:

The first number 235 is the overall width of the tread in mm.

The series or 45 is the sidewall height but as a percentage of the width or 235mm*.45

Here is a cool app that calculates the diameter and other dimensions http://www.discountpartcenter.com/tirecalc.html