Backspacing vs offset?

[B-ROCK]

Hey all, I've been reading on here for a while and have a question. I'm lifting my 93 fullsize blazer ( lift and tires sitting in the garage) I'm going to run 4inch of lift and 295/75r16. I'm unsure of what rims to get due to backspacing. Pretty much everything is a 4.5inch backspace. I want 16x8's. I was hoping to get something that did not stick out as much as a 4.5backspacing due to laws where i live. http://www.gmt400.com/forum/showthread.php?1551-Need-help-on-alignment-issue!!! 2nd pic down is 4.5bs. When reading specs on rims they have offset and backspace. Now my problem is, that in my head they achieve the same thing. For example ( argument sake) a 4inch backspace would stick out just as far as a 5inch backpace but with negative offset. Is this correct?

Most of american racing stuff is 0 offset and 4.5bs. Now when it shows the offset in mm, is it actually millimeters meaning 1/10th of a centimeter?

Sorry for the long post, but i'm getting so close i can taste it.

Thanks Brock

 

[JB11]

http://www.autolounge.net/calculators/tirespacing.html

Check what backspacing the lift requires and go from there. I had a rancho and it required a max of 4.5"bs

 

[B-ROCK]

Its RCX so they say factory backspacing. There isn't much out there in a 16in with factory backspacing. 4.5 seems to stick out from the body to much for the law up here.

 

[JB11]

I think factory may be 4.5 on our OBS trucks, not sure. They shouldnt stick out unless your getting 10" wide although the spindles may push them outward too.

 

[Loss4wrds]

Stock wheels on my truck were 16x7 with 5.5" backspace or +38mm offset.
Offset and backspacing are just 2 diffrent ways to measure the same thing.
I really like this tool for compairing wheel and tire combo's
http://www.rimsntires.com/specs.jsp

Add in the specs for the stock wheels as listed above and plug in the new combo and check out fitment at the bottom of the page. This is how I figured out the offset i wanted when I custom ordered wheels.