Selecting new rear meat

[BR3W CITY]

I guess the title of this could be taken multiple ways lol.

with my swap done, I need to get some more traction on the rear, and a big part is upgrading my 15x8 aluminum MT wheels to something a bit wider.

i have considered getting steel wheels to widen, but with that I face the issue of determining the offset/backspace and width of the wheels. My initial thought is a 12" wheel (since I am tubbed to the frame width), but I had also considered a 10" if I could get the right look and performance. Soooo.....

1. What size tires should I be looking at? Its street vehicle but I DO like to get into a little action on the street occasionally, as well as SOME strip time (a few weekends a year). 295/65/15 seems popular, are there enough choices in this size?

2. HOw the heck do you determine the correct offset/backspace for a custom widened wheel? I have some people telling me so do it off of the tire, or how to determine it off of the rim....but I don't have either yet...only the 8" rims on it now.

3. I'm also ok with buying a set of DR's or slicks for track days and keeping them on an extra set, so if this affects #1, please take it into consideration.


Thanks for all the help!

Quick pic of the tubs mocked up. Inner width won't be a problem.