back spacing

[malibus~most~wanted]

what exactly is backspacing? im new to the rims and tire specs. im looking at a set of cragar soft 8's 17/8 in the front and 17/9 in the back. i have the stock v6 sprins front and rear, but i installed the heavy duty coilovers from moroso which brought the wheels out of the wheel wells some. im thinking that they will fit. tire size for front will be 255x40x17 and for the back 275x40x17.

 

[MEGABU]

backspacing is the distance between the mounting surface of the rim(where it contacts the brake drum/rotor) and the rear lip of the rim. lay a straightedge across the back of the wheel & measure from the mounting surface to the bottom of the straightedge. the number you see is your backspace.
sometimes you'll hear the term 'offset' where it applies to wheels, but despite what some may think, it's different from backspace. offset is the measurement of how far off-center the mount surface is. for instance, a 15x8 rim with 3.5" backspace has an offset of negative 0.5". a 15x8" with 5.5" backspace has an offset of positive 1.5". i hope i didn't confuse you, i do that sometimes. 8-[