Question about backspacing

[01poison320]

Ok I know how to measure backspacing and what not but what I dont quite understand is what does backspacing even do? what is a good amount of backspacing? I am just kind of lost on those main concepts :shrug: and I'm trying to figure it out because I am working on buying some 15x10 weld prostars and just dont know what to do for the backspacing. I measured from fender wall to the rotor and got about 7.5" so if anyone can shed some light on me thanks.

 

[01poison320]

Anyone at all? I gotta figure this out cause I'm planning on buying the wheels on friday and wanted to get some opinion/knowledge on what to do and what size b/s to get.

 

[kruck5.0]

Its just used as a reference as to where the wheel will be in the wheel well. On the wheel it is the distance from the edge of the wheel lip to the flange that bolts to the hub or axle. To measure that you can take a straight edge or board and measure the distance to the flange. 6.5 inch back spacing works good for a 15x10 on a stock length 8.8.