Anybody know if it is possible to calculate the wheel offset by just the backspacing? I am interested in some 3 piece wheels , but the offset is not stamped on the wheels. The specs are:

8.5x18 with 6 7/8" backspace
11.0x18 with 7 3/8" backspace

Guy says he used them on his 993 C2s with spacers. Just wondering if I can get them to fit on my 997 C2S.

Any insight would be appreciated.

 

I found a page at Mickeythompsontires with a conversion between backspace and offset.
Not surenifnthis cut and paste will work:

TO CONVERT OFFSET TO BACKSPACING:

For positive offset wheels: (Wheel Width +1)/2 + (offset * .03937)

For negative offset wheels: (Wheel Width +1)/2 - (offset * .03937)

TO CONVERT BACKSPACING TO OFFSET:

Backspacing – (Wheel Width + 1)/2 * 25.4 = offset

Hope this helps.

 

As an example on an 11" wide wheel the centerline for a zero offset would be 5.5", 1/2 the width. Take the backspace you noted and subtract 5.5" (zero offset) from the backspacing of 7 3/8". You get 1.875" as the offset. Convert it to millimeters by multiplying by 25.4 and you get 47.6 as the offset.

 

Thanks for the replies guys.

 

Here's our link on offset.