I was lookin on ebay and noticed how the wheels on display here.

http://cgi.ebay.com/ebaymotors/ws/eB...tem=8034983427

show a variety of the wheels and in the picture I noticed one wheel has way more concavity then the other wheel. In this picture is the top one is a 7 and the bottom one is 10 inches wide. This to me is like a whole different rim in this picture.

 

they could actually be the same size. backspacing (aka offset) determines the 'concavity' of a rim.

 

yea there both 17's but one is 8 other is 10 wide.

 

o i c

 

no, rim width is different from backspacing too. they could both be 8" wide for example.

When you buy a rim there are four measurements to go by.

bolt pattern - i.e. 5x114.3mm for our cars
diameter - i.e. 17" or 18"
width - i.e. 7" or 8.5"
backspacing or offset - i.e. 12mm or 32mm and so on.