AR61 wheels backspace and offset

[m_m70]

picking up some Outlaw 1 AR61 15x8 wheels. They have a 3.75 backspace and -19 offset. I now the 3.75 backspace will work but the -19 offset has me confused and not discussed a lot. Will I be ok with these? I know that I'm limited to tires with the 15" rims but I like the look of the 15's and have the tires already.......

 

[serial car restorer]

Offset and backspace are two different ways to measure the same thing. If you understand backspace, use that and don't worry about offset.

 

[serial car restorer]

Here's the details. First, an 8" wide wheel is actually about 9" from lip-to-lip. The 8" measurement is at the bead seat.

Backspace is simply the measurement from the hub mounting face to the inner wheel lip. So with 3.75" backspace, that wheel will have 5.25" from hub mount to the outer lip.

Offset is the difference between the hub mount face and the centerline of the wheel. In the case of our 15x8 wheel, the centerline of the lip-to-lip width (9") is 4.5". Offset of -19 means the hub face is 19mm inboard of the centerline. 19mm is basically the same as ¾", so 4.5" - .75" = 3.75”. Same spec.

 

[Pops68]

These 2 pics may help clarify things a bit.

 

[Pops68]

Wouldn't the offset determine how far either in or out the tire would be??? Negative offset, the tire is farther out and positive offset the tire is more in towards the vehicle??? Could this affect rubbing and/or turn radius???

 

[serial car restorer]

Wouldn't the offset determine how far either in or out the tire would be??? Negative offset, the tire is farther out and positive offset the tire is more in towards the vehicle??? Could this affect rubbing and/or turn radius???

Yup. But you can tell all that from the backspace as well. Same data, just different way to state it.

I sold tires and wheels for over 20 years in the 70s, 80s and 90s. When fitting something totally custom (home built hot rods, for example) or on 4WD rigs I would use backspace (and front space) to verify clearances. On sports cars and such I used offset primarily, generally to calculate small changes (5mm or so) compared to the OE wheels.

 

[Pops68]

thank you!