Wheel Measurements

[KiDyNomiTe]

OK eberytime I look at rims they usually have numbers like: "17x7.5" for rims, and "215/40-17" for wheels. there are more numbers but I can't remember them.

Could someone explain what each of those numbers mean and also what offset is. How do I tell what ris will fit with the certain tires?

[boywonder]

SCC is a great source for stuff like this. here's the sportcompactcarweb.com link to the article: link

[Jeff240sx]

Geez.  Just type.  No-one wants to search through pages of scc online.
215/40/r17 is:
215 millimeters wide.  40% of the width tall.  r=passenger radial.  17= rim diameter.
So that tire would be 215 millimeters wide, 82 millimeters tall, and can only be mounted on a 17 inch rim.
As for rims.
17x7.5
17 inches in diameter and 7.5 inches wide.  
I would assume the other numbers you forgot would be something like:
Bolt pattern - 5 x 114.3
That is 5 lug, each lug is 114.3 millimeters from the next one.
Offset is:
Imagine an invisible line down the center of a rim.  On an 8 inch rim, it would be 4" into the rim.  Now you put an offset in there.  If the place the rim mounted to your hub was 4" in an 8" rim, it would have 0 offset.  
If you moved the mounting surface to the edge that shows to everyone, you would have positive offset, measured in millimeters.  Stock s14 SE alloys are +40 offset, or 40 millimeters to the front of the rim.  Negative offset is towards the hole in the rim, moving the mounting surface towards the car.
Hope I helped a little!
-Jeff