[djp2]

i have a 2004 rado exteded cab z85 and i want to get 15x8 rims what should i get and what size ? dont want any rubbing issues or sticking out of the wheelwells to far any suggestions?

 

[08Canyon]

What should you get, and what size? You already said you want 15x8.
So I think you should get 15x8.

Unless you have a 2wd Z85, then an 8" may be too wide as you can't get a very wide/tall tire on that truck.

Don't want rubbing issues? Can't help you there. You didn't specify what tire you have now.

 

[djp2]

i want 15x8 rims with 235 75 15 what backspace should i get

 

[08Canyon]

I think the 235 tire is too narrow for an 8" wide wheel. Especially a 75 series on a 15".
However, check the tire manufacturer web site for wheel recommendations for the tire you are purchasing. I'd suggest considering a 7.5" wide wheel (max) for a 235 tire.

To maintain an appearance similar to factory, I'd get around 5" backspace. A 4.5" backspace will poke a lot, 5.5" backspace is too inward.

This link will help you read offset values for different wheel widths to achieve the backspace of your choice.

Notice how the offset values change to maintain the same backspace as the wheel width is modified.
Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

For reference, your Z85 wheel should be 6.5" wide with +41mm offset. The width is printed on the manufacturer sticker on the driver door jamb near the latch. The offset value is stamped on the inside of the wheel (removal from the truck is necessary to see).
So remember, closer to 4" makes it stick out, closer to 6" pulls it in (relative to stock).