Here is a blurb from our Build Your Own Rear Wheel Product:
https://www.hyperracing....ore.aspx?product=842-000Terminology: Offset and Backspacing
Always refer to the wheel width stating the outer half first and the inner half last. Example: a 10" wide wheel with a 6" outer half and a 4" inner half would be referred to as a 6" on 4" wheel. You'll also hear the term "Offset" or "Backspacing", these refer to the inner wheel half size. A 6" on 4" could be stated as a "10" wheel with 4" backspacing or 4" offset".
Typically the left rear wheel on a 600 is a 6" on 4" or a 7" on 3" if you run 10", or a 5" on 3" or 4" on 4" if you run an 8". Many teams are starting to run an inner bead lock on the left rear to keep the tire from peeling off the bead on a rough track.
The 600's right rear offsets can vary even more, and axle width is a determining factor. For standard 53" Axles, an 8" on 5" is normal. Many Z-link rear suspension cars use a 7" on 5". For the wider 55" or 57" wide rear axles, you can also use wheels with less offset which moves the wheel center in by running a 7" on 6" or even a 6" on 7".
If you want to get the right rear out but don't have enough axle length, you can go to a 9" or 10" outer wheel half with a 2", 3" or 4" inner.
270's typically run 5" on 3" on the left rear and a 6" on 4" on the right rear.