the reason its thicker is becasue the 40 is an aspect ratio depending on the width of the wheel. s0 215 40 17 and a 205 40 17, 40% of the width is the sidewall height, theres alot more to figuring it out, but thats just basic. and yes the 205 40 17 will fit on a 7.5 wide wheel but i would go with a wider tire to protect your wheel edges.