I've read the other post about offsets, and I've done a search, but I still have questions about it. I've spoken to a local Discount Tire rep about wheels, and I've been told I have 4 3/4 lug spacing (that's 120.65mm, right?) and that I need a wheel with 0 to +6 offsets. Does this all sound right?
Also, if I want to put a 4th gen type of wheel, what type of spacer is needed?

I'm just frustrated at finding nice wheels but the wrong offsets. I'm trying to educate myself on it so I can refine my search.
Thanks.

 

What brakes do you have on the front of the car?

Edit: And is the car lowered, or do you plan on lowering it- and if so how much?

 

The brakes are currently stock. I'm about to install a Baer Touring kit (12in rotor) on the rear, and then I'll get their Track (13in) for the front. As for lowering, I'm looking at a coil-over kit, so I'll lower it about 1- 1.5 inches.

 

I'll give you my max offset with what brake package offset I am running just for reference. It is the maximum I can sit the tire outward in the fenderwell without it hitting the fender lip. My car is extrmely low yet stiff, and with a 25.7" diamete tire it will NOT rub the inner fenders anywhere, but by very minimal margins. I could not go any more outward with the outer edge of the tire. Also note that I run about -1* camber which also tucks the top of the tire in slightly.

With that said, I run 8" wide rims and 245/50-16 tires.

Standard 1le brakes are the factory standard. The front Iroc rims are a 0 offset. Again, this is the standard for any performance package IROC stock from the factory.

My brake face is +.019" from the 1LE (I stick outward .019" more)
I run "rear" IROC 16x8 rims with a -16mm offset (-.630). So, in order to set them outward I run a custom made hubcentric wheel spacer which I made +.818".

My total setup is at the outer edge of the rim compared to stock is +.209" (Roughly almost a 1/4", 7/32 to be more exact) and that is the max outward I can get safely without definately no chance of the tire hitting the fenderlip.
When I use to turn full lock, the inner tire would rub the inner fenderwell due to me running factory 15" a-arm stops which allow the wider 16x8 rims to hit. The stock 15x7" rims would not. 16" rim cars from the factory had different steering stops mounted on the A-arms to prvent this. I welded mine with more material and grinded them into shape to help prevent this from rubbing instead of finding 16" rim A-arms. Wider rims will rub no matter what you do unless you really expand your turn radius limit.

 

Here is a shot showing how outward my tire sits near the fender lip. Note the camber that pitches the top of the tire inward so it will not make contact (-1.0* camber). If I decreased it to 0* camber it would rub(just for reference, noone would ever run 0* but common is only around -0.3*

 

Thanks for the info, I'm just trying to make sense of all the numbers now.
I noticed you have the 2.8L; me too, I'm starting to build it up to take a V8 though. You say all F-body's had the 1LE brakes? Even the V6's?
I'm also running the same tire/wheel size that you have, I just want to step up to a 17x8 in front and 18x9.5 in back. I know I can change the length of my rear end to make any wheel fit, so my biggest concern is the front. Your front wheels have a 16mm offset, so you made a .818 inch spacer to make them fit? Thos eare stock wheels too, right?
Are there any problems using a spacer on a daily driver? I've heard there are potential problems, but I don't plan on racing the car.

 

All stock 2.8 cars had the standard 10.5" brake system which is -.318"(inward towards the center of the car) from the 1LE brake mounting surface offset. to set you car exactly at its max front track width like mine without rubbing, you will need to purchase an 8" wide rim (any dia, 16,17or 18" as long as the total tire dia is about 25.7") with a positive offset of +.525" or to round down to a safer round figure of +13mm offset rim.

A stock Iroc front rim is 0 offset. That rim on your setup without a spacer on an IROC with iron calipers (-.318") will set inward aprox 1/2" (-.548") from what I have shown in the picture above without any use of spacers. Just a stock 0mm Front rim and standard non-1LE brakes. Cars with this setup had larger turning stops to limit there turning radius so they would not make as sharp a u-turn as your 15" rim V6 would stock. Bolt on IROC "fronts" onto your car and they will rub the inner fenders before full lock of the steering wheel left or right.

Best to either-
1)space them out with a 3/8" spacer to get them more like the 1LE overall offset (you'll need longer wheel studs to do this)
2) or, buy rims with more positive offset range from a min +9mm to a max of +14mm on the iron brake setup
3)add Baer track kit- (same as 1LE brakes offset) and run the stock 0mm offset (minimum) to a +5mm max positive offset rim

Those are your options base on how much you want the tire to set under the fender lip and have a decent turning radius without rubbing. And again, those figures are pertaining ONLY to an 8" wide rim.

EDIT: I went back and double check my figures to verify facts and I corrected the info above. I had first mis-listed the IROC fronts as +16mm when they are 0mm/ and had listed the IROC rears at 0mm when they are -16mm. No harm no foul, got it corrected in time to verify info to be accurate and trustworthy before anyone commented - I do occationally slip up on figures going off of memory, but I always try and confirm what critical measurements I list in order to catch such possible human errors. I can be wrong sometimes and willingly admit it.

 

And to answer this honestly, most spacers up to a 7/16"(.4375" thick) are fine as long as you are using stronger racing studs (tensile strength of 190,000psi) and there are plenty of threads for the lugnuts to grip to (hence why longer studs are needed on any stock 3rd gen when trying to use spacers larger than an 1/8".

I said above I had made a wheel spacer of just over 13/16" thick (.818" thick to be exact) but the crucial key to this is it was custom made to be "hub centric". What this means is the center hole is machined to exact stepdown tolerances of my custom aluminum hubs and it press fits onto the center hub snout with is a 2.78" and then steps up to a 3.06" inside dia. Gravitational & centrifical forces applied to the wheelstuds sideways will not cause the longer studs to exceed tortional forces on the studs due to the rim being mounted 13/16" off the hub face and leverage braking the studs- because, the center "hubdenteric portion of these custom 13/16" spacers will rest "as one" with the hub and hold the stud position in tact without bind. A non hub centric spacer can fail due to the forces on the studs rather than the hub. If you llok at regular over-the-counter wheel spacers, you will see that the center hole diameter does not fit snuggly over the center portion of the hub AND the stud holes on the spacers are not a percise tight fit. You can clearly see in the picture I show below that the ones I made are pressfit onto both the center hub, and the studs without slop or possible tortional flex movement.

 

And the finished product.

I will also note that the rim center fits "hub centric" onto the remaining portion of the expose center hub which is 2.780"

Also I will note that those are not the ARP studs I used, those are the original 1/2" studs that GW fitted into the hubs when they made them for me. I then pressed in 1/2"x 2.970" ARP racing studs into the finished assemblies.

Everything was press fit to exact tolerances in order to run those thick wheel spacers which allow me to run 4 "rear" IROC -16mm Iroc rims on the car for rotation purposes without having to dismount the tires from the rims to rotate.

 

Thanks for all the info! Now I have someplace to start. I do plan on getting the Baer Track kit, so I'll keep looking for a 0 to +5 offset. The downside is that I haven't seen many wheels available with the right lug spacing and that offset.

I see you've kept 8in wheels on all 4, with 245 tires. I currently have the same setup (I've noticed the rubbing wheels, I just haven't placed a new turn stop), but I'd like to run 275's in back. I took a measurement today, and it doesn't seem feasible without a mini-tub. Have you looked into that probelm already? or seen a solution?

 

Never even bothered to measure anything because I will never run different rims. This is just a full time street car and will never be altered for serious racing. I like the abilty to rotate tires on a full time daily driver.

 

I hear what your saying. I'm thinking about getting non-directional tires so I can at least rotate left-right.