well im looking at some rims on ebay that are
FRONT WHEEL SIZE 17 X 9 1/2" 56mm OFFSET
REAR WHEEL SIZE 17 X 11" 50mm OFFSET

first off what does the 56 mm offset mean and the 50mm

also, what size tires fit on these?

would it be 275/35R17 and 315/35R17 respectively?

and when i have to beat in the fender what exactly does that intail?

and also i think the other option is to get 17" x9.5 and 18"x10.5 which would be better the 17" on both rear and front or 18 and 17?

yea here

they are the Z06 rims
REAR WHEEL SIZE ( 18 X 10 1/2" )
FRONT WHEEL SIZE ( 17 X 9 1/2" )
OFFSET 56mm

which would be better for over all performance?

 

Offset is the distance the centerline of the wheel is offset from the face of the hub mounting surface.

Those are the correct wheel sizes/offsets for the 4th Gen. I have that exact setup, with htose tire sizes on my green 94 Formula.

http://cjcfo.fbody.com/members/injun...osD/SLP27a.jpg
http://cjcfo.fbody.com/members/injun...tosD/SLP18.jpg

About 50% of the installs of these wheels in the back require cutting the outer edge off the jounce bumper bracket, hammering the inner fenders, and even recentering the body over the rear axle with an adjustable panhard rod.

The Z06 wheels may be "reproduction" wheels, because that is not the OEM wheel offset. The Z06 17x9.5 factory wheels are 54mm. And those, or the 56mm offset will work fine in the front. Anything from about 45-56mm will work in the front with a 9.5" wheel width.

The 18x10.5 factory Z06 wheels have a 58mm offset, and that is a problem with the 4th Gens. It puts the insdie edge of the tire pretty hard into the inner fender liner, and would require substantial fender pounding or a spacer to eliminate the problem. A 56mm offset on the 10.5" wide wheel would give it just about the same backspace as the 17x11 50mm offset wheel you mentioned above. I think I have seen someone post that they found 54mm offset Z06 18x10.5, which would fit even better.

Which is the best for performance?..... define "perfomance". Straight-line traction, or going around corners at high speeds?

 

i guess corners at high speeds...

i know lower profile is better for corners and more rubber is better for launching...

yea they are replica rims both of em.

how long does it take to do that hammering at the fender?

 

Even the benefit of "lower profile" is questionable on a solid axle setup. There just isn't enough compliance on each side to allow the tires to individually operate at the correct angle to the road surface. IRS cars can use these super low profile tires, but how much you gain with a solid rear axle is open to debate.

I had to hammer quite a bit to fit 315/35-17 BFG Drag Radials. But I've seen people post that they had to do absolutely nothing to fit 315's with the 17x11 50mm wheels. Seems to vary based on production tolerances. Hard to believe that you could get away without cutting the edge off the jounce bumper bracket:

http://cjcfo.fbody.com/members/injun...A/FendMas2.jpg

I think a lot of people just accept the fact that although the bracket sticks inside the back of the wheel at normal ride height, they can't jack the car and allow the axle to fall to full drop without catching the bracket on the wheel.

I had to hammer a lot, but I also knew I would be mounting some large slicks, and didn't want to have to go back and hammer some more. After you get done hammering, a thick coat of spray-on rubberized underecoat will hide the carnage.

http://cjcfo.fbody.com/members/injun...A/Drivhamr.jpg