Tires: OEM Rim size, aluminum alloy wheels, torsion spring

Question
I'm in the market for some new tires for my 1997 Z71...  I was wondering what the OEM rim size is for that truck (with the aluminum alloy wheels)...  THe truck has 115K on it with only two sets of tires so far  (original on/off road and then Dueler MT off road) I got 50+ out of each....  The second set were one step higher 285/75R16 and I want to go to 305 (which I've seen some people do with this type truck)  The one over size had a little rub on the sidewall with the torsion bar (front stabilizer)...  I understand that the front torsion "spring" can be cranked up a tad to get a bit of lift in the front whi8ch is what I plan to do for these (<1") wider tires (which is < 1/2 on each side(wall))  I'm looking at 305/70R16 the section width of which is quoted for a 9" rim...  I'm guessing my rims are narrower and thus will make the tire slightly narrower at the sidewall (but slightly taller I presume)...  Any advice you can give here would be greatly appreciated...

Thanx,
mj

Answer
Mark,

Sometimes there is a bit of confusion with regard to vehicles and their designations.  A Z71 is a Chevy 4X2 pickup - right?  But my book only lists this as a C1500.

And just to verify, check your vehicle placard, which is located on the driver's doorpost.  Is the tire size P235/75R15?  Is the rim size there as well?

If this is all correct the rim size is 7".  

But I noticed that you mention 16" tires, which in my book never appeared on anything but K1500's (4X4's ) and larger.  But reading between the lines - these had a 6.5 steel rim and a 7" alloy rim.

If that last part is true, then the maximum tire size that fits is 265/75R16, meaning the 285/75R16's shouldn't have been put on.

So you need to get new rims if you want to go 305/70R16 - at least 8"  Otherwise, you will have a vehicle that is sensitive to road variation, ruts and the wind.  It will wander around without appearuibng to know which direction it is going.