ok here it is how to tell what all those numbers mean.

the first numbers are the width of the tire in MM

the second is the side wall hieght. it is the percentage of the with

the thrid is wheel diameter at the bead.

ok here goes a 245/45/17 is
245 mm wide
45% of 245 is the side wall hieght witch would be 110.25mm
and it fits on to a 17" diameter wheel.
the over all diamiter of the tire is (110.25mm X 2) + 17"
220.5 do a metric to english conversion http://www.worldwidemetric.com/metcal.htm
is 8.6811" +17=25.6811" in diameter

the other numbers and letters are wear rating temp and traction.
i don't remember some of that stuff but here is what i can tell ya
wear rating is something that pretty much know one out side of the tire industry understand.
a good way to go is for every 100= aprox 10000 miles, this is on a car with a near perfect alighment(some cars come with a sporty set up that tends to promote tire wear), proper infaltion, rotated properly, and a sane indiviual driving.
the traction rating a-aaa is a skid rating it is cacluated buy taking a certian weight car up to a certian speed and locking up the breaks and seeing how long it takes the car to come to a dead stop. it has nothing to do with acceleration.
the speed rating if i remeber right a dot approved tire has to have a rating of aound (non rated tire) 130 H is like 170 and z being 210 there are other ratings but those tend to be the
most common
temp is something about how a tire disapates heat or something like that i honesly don't remember
i have just seen a lot of will these tires fit my wheels or stuff like that and thought this might be useful info for some people.
if i am wrong or you have more accurate info please correct me its been nearly three years since i messed with any of this.