Wheel Confusion - Back Spacing

[Bronco648]

Truck: 2011 RCSB XL with the stock steel wheels (15")

I am looking for some Ranger/Explorer or after-market rims to dress up the truck somewhat. But, I'm confused by the information in the Wheel Fitment Guide:

The basic Ranger wheel diameter is either 14×6 or 15×7 inches.

Stock Backspacing is usually 4.5 inches.

Recommended backspacing on a 15×7 wheel is 3.75 inches with -6mm offset.*

So, if I have stock rims (15 x 7) with 4.5" back spacing, why is it recommended that I find something with 3/4" less back space?

Does anyone know what the offset is for stock steel wheels?

TIA, Dave.

 

[Uncle Gump]

I'm pretty sure nearly all factory wheels are 4 1/2 inch BS.

Aftermarket wheel companies are about style... they also have an engineering department to ensure their safety. But most aftermarket wheels for our trucks in either 7 or 8 inch wide use that 3.75 BS number. So I'll say it's an industry standard... outside of factory.

That little less BS allows for a slightly wider stance... also pushes the typically larger tire outward to allow it not to rub on the frame when going lock to lock.

 

[pjtoledo]

15 x 7 and 16 x 7 factory aluminum wheels have -12mm ( 1/2") offset. it's stamped/cast on the wheels.
that gives a 4.5" backspacing.

 

[Bronco648]

Thanks guys!

 

[don4331]

So, if I have stock rims (15 x 7) with 4.5" back spacing, why is it recommended that I find something with 3/4" less back space?

Most of times, when people are installing aftermarket rims, they are also in process of installing larger (wider) tires. So, the new tires don't rub on anything, the rim manufacturers use less backspacing which pushes tires away from sharp objects. (On newer vehicles, aftermarket is less concerned with CAFE - OEM nice flush rims are better for fuel economy).

'83-'11 Ranger OEM vary from 0-12mm offset. The orginal 14x5 rims have 3.5" backspacing to achieve that; the later 15x7 & 16 x7 have 4.5".