I too was confused about backspacing as compared to offset. The following link may help. http://www.bigcustomwheels.com Just click on the sizes guide. This will provide a wheel diagram where you can input tire size and offset. The diagram will convert offset to backspacing and visually show the different configurations. Best of all you can input for two different sizes to clearly see how two tires will compare!!

 

thx for sharing. I'll have to bookmark that page for future reference.

 

I'm not sure if you found your solution, but my 04 had a horrible shimmy after using the parking brake, after a few kilometres it would go away....I found it was a 'X' shaped scissor assembly that was used to apply the drum type parking brake inside the hub of the rear disc brakes. The problem was the 'X' would rust together after non use. A little WD40 to break it apart and some good brake lubricant upon reinstall and voila problem solved.