17X11's on back of 02 Z

I've seen several different offsets for those Black ZR1 wheels, +36, +50, +53, and + 56 or 58 i can't remember what the biggest i saw was. i want to put 315 35 17's on it and want to know which offset i need to get for the car. any and all advise is appreciated.

The 17x11 ZR1's that I have seen are available in 36.5mm and 50mm offsets. The 50mm is the one you want. That puts the outer edge of the wheel/tire just barely under the fender, when you look straight down from above. The 36.5mm offset will stick out about 1/2" more. You may still have to hammer the inner fender, roll the fender lip and cut the edge off the jounce bumper bracket - varies a lot from car to car.

If you do the math the 56mm offset on a 17x11 will have a backspacing of 7.7 something inches, and thats less than what afs wheels advertises there 50mm offset wheels at which is 7.93 inches? i dont really get why its advertised like that. am i right on this? cause if i am thats what im gonna go with

You are not calculating the backspace correctly. You are not including the width of the flange that retains the tire bead. The wheel "width" is measured at the point on the rim where the tire beads seat, not at the outside edges of the rim.

Backspace = wheel width/2 + offset + bead retaining flange

If you convert the 50mm offset to the 7.93" backpace that AFS advertises, you will find that the wheel has an 0.461" flange.

11.0/2 + 50/25.4 + 0.466 = 5.500 + 1.969 + 0.461 = 7.93"

All this matches on my AFS ZR1's.

If you do the same calculation with a 56mm offset (which I've only seen offered on the 17x9.5" AFS wheels), you get an 8.17" backspace, and I can assure you it will not fit on a 4th Gen F-Body. But its your $$$$$, so if you don't believe me, buy what you want :)

oh ok I was unaware of that, i always thought they were measuring the width of the entire rim. the +56 offset, how would that clear on the car? i dont want to have to roll the fender if i dont have too.

I'll try this one more time..... where are you finding 17x11 ZR1 style wheels with 56mm offset? I explained that they wouldn't fit on a 4th Gen, because the backspace is too large. The 50mm wheels put a wide tire into the inner fender sheet metal, and on most cars (but not all) require that you hammer the inner fenders quite a bit. You also need to cut the outer edge off the jounce bumper bracket, or the inside of the wheel rim will catch when you jack the car and the axle drops. Adding another 1/4" to the backspace will simply put the inside edge of the tire another 1/4" deeper into the inner fender sheet metal. I guess you could hammer it even more, but its going to be a lot of work.

All this is based on my personal experience with the 50mm wheels.

http://cjcfo.fbody.com/members/injuneerzz@aol.com/PhotosA/Drivhamr.jpg

the web site is http://www.performancewheeloutlet.com/, i'm sorry if i pissed you off or anything, they only have the black on a 30 something 53 and 56 offsets thats why i was asking how they would fit, sorry for the trouble. they got the chrome ones in the 50 offset, i'll get them if i have to, how does the 50 line up with the outside of the fender on a camaro cause arent the birds wider?

I see the wheels you're talking about... first time I've ever seen 17x11 ZR1's in some of those offsets. I've never seen them in anything other than +36.5mm (the original - true - Corvette ZR1 offset, the ZR1 Vette had wider rear fenders) and +50mm (the offset that GM used to fit 17x11's on the rear of the '96 Corvette Grand Sport, which had standard 'Vette fenders).

I'm running 17x11" +50mm ZR1's with 315/35's on the back of my Z. The tires sit barely inside the outer edge of the fenders at the top. I installed them, closely following the advice and pics from Injuneer, and have no contact issues whatsoever. But believe me... they're a tight fit.

As Injuneer suggested, you've got to do some pounding on the inner fender, and attack the jounce bumper/bracket with a grinder, in order to properly install the +50mm... but when you're done you have the best possible fit. Let's face it - GM never intended to put 315's on the back of the Camaro.

The +50mm is the perfect offset... any smaller offset is asking for interference with the outer fender; and larger offset is going to require more hammering and grinding to avoid interference with the inner fender.

This is the internal clearance of the 17x11 50mm with a wide 315/35 BFG Drag Radial:

Left side:
http://cjcfo.fbody.com/members/injuneerzz@aol.com/PhotosC/TirClr2L.jpg

Right side:
http://cjcfo.fbody.com/members/injuneerzz@aol.com/PhotosC/TirClr1R.jpg

Those are from slightly different angles.... the left side it straight on, showing the true clearance, the right side is looking a little more from an angle, so the clearance looks larger.

This is the right side, with the camera on the ground, looking straight up (I no longer have the Spohn LCA's with the big adjusting nut.... they were too close to my 28x10.5-15W slicks - I replaced them with newer Spohn LCA's):

http://cjcfo.fbody.com/members/injuneerzz@aol.com/PhotosC/TirClr5R.jpg

Rear view..... they are just under the lip of the fender, when looking straight down from above.

http://cjcfo.fbody.com/members/injuneerzz@aol.com/PhotosC/RrView01.jpg

The +53mm offset would only move the wheel in 0.12" (about 1/8"), and that would probably work with just a few extra whacks of the hammer. The sheet metal that you need to hammer is fairly stiff at the bottom, since it has a thick metal channel behind it for reinforcement. And when you start hammering a little higher, you are hammering on the point in the body that the "bolt" that the rear seatback rests on is behind it, and if you don't keep the seat in place when you are hammering, you screw up the seatback position.

The +56mm is going to be too close to the inner fender, and close to a stock LCA. With a good tubular LCA, you might have more room.

I had not seen the PWO wheels before. I tried going to that site a few months ago to look at their Silverado SS replicas, and the site would not connect.

If I sound frustrated, it because I have typed most of the above info about once a month for the last 5 years :)

If I sound frustrated, it because I have typed most of the above info about once a month for the last 5 years :)
A few more of these 17x11-315 threads and you'll be at 20,000 posts!

Injuneer is that a damn 4 inch pipe in that picture? that thing is freakin huge.

Injuneer is that a damn 4 inch pipe in that picture? that thing is freakin huge.
You mean this......

http://cjcfo.fbody.com/members/injuneerzz@aol.com/PhotosS/DCP03556a.jpg
http://members.aol.com/InjuneerZZ/images/Photos/Susp.jpg

That "was" a Mufflex 4" catback..... its no longer there, replaced by dual 3" dumping in front of the axle.....

http://cjcfo.fbody.com/members/injuneerzz@aol.com/PhotosL/DCP03675a.jpg