What is backspacing?

[grdprx]

I'm got to say it again, I'm a rookie.  I'm a novice... 

I don't have a clue what backspacing is!  It sounds simple, but I don't know what's being measured.

I have a 68 charger, I'm planning on 235/60/15 in the front with 275/60/15 on the rear.  Is there anything I need to know about backspacing in this set up?

I have already bought my wheels, hopfully they have the right backspace.  What and where do I measure to find out? 

[Ghoste]

What it means in essence is that portion of a rim where the axles bolt to is not necessarily in the center of the rim.  You could have a 7 inch wide rim but the center disc isn't always 3.5 from the front or back surface, it could be backspaced so that the tire is effectively brought further into the wheelwell.
Does that make sense?

[grdprx]

OK, that makes sense.  So it's whatever amount the bolts are off set from the center of the wheel.

Would my tire picks require backspacing?

[suntech]

That was not a correct description of backspacing!!! This was actually explaining the offset.
Backspacing is the distance you measure , using a straight edge across the inside of the rim, and measure how deep in to the rim the mounting- face is .
A 10 inch rim, with the mounting face in center, has app 5,5 backspacing, since a 10 inch rim measures app 11 inches outside width.
Did that make any sence??

[SnoPro440]

This may help you too.

http://www.wheelvintiques.com/pdfs/wheel_fitment.pdf

[grdprx]

Thanks for all the info, that PDF really helped.  Pictures are great. 

I have 15x7 wheels with 4" backspace.  Sound about right?

With that said, will 275 60 15 work on the rear?

Thanks again!

[Ghoste]

On rereading my description I can see how it could be taken as a description of offset but it was backspacing I was trying to explain.  The only difference between the two really is that one measurement is taken from the edge of the rim and one is from the centerline of the rim.  Throwing the centerline part in my description and not talking about the edge screws it up.  My bad, I was trying to say the same thing though. 

[Musicman]

Remember, before you can calculate the required wheel Backspace and Offset of any particular wheel & tire combo, you must first get out there and find out what you have available under your fenders... That's step No.1... The rear is pretty straight forward, but the front is a little more involved because the wheel moves side to side, and those clearances must be checked. Remember, your not just measuring for wheel clearance, your measuring for the fitment of the entire assembly (tire width, tire height, etc)