It would end up with 41mm offset. That will almost surely be too much offset and backspacing with a 315 tire. The most offset I've seen anyone use on an early C4 with 11" wheels is 36mm (e.g. a genuine ZR1 wheel), which gives 7.42" backspacing (via posts here on this forum). I would actually think even that is cutting it too close on the inside, but like I said I've never tried it. So that is the most offset/backspacing I'd want to try. To get there with your plan would require a 9.5" wheel with 17mm offset, and then you'd add the 1.5" to the inside. If you did that and it turned out to have a few mm too much offset (it would not be more than 4mm too much for sure), you could then easily use thin spacers to push them out (subtract offset) and the clearance inside that you need. For that minimal of a spacer, you'd be fine with the stock wheel studs.

If you decide to start with 22mm for the 9.5" wheel, you will definitely need at least a 5mm spacer. You may be able to use that much spacer with the stock wheel studs, but I'm not sure. You need to be able to get six turns of the nut onto the threads to be safe. If you needed any more than that (say, 8-9mm), you'd surely have to get longer studs. That's not major surgery on the fronts: those hubs are easy to remove and replace the studs. The rears are a little more involved, especially (from what I've read) on the early C4s with the drum parking brake. But it's still very doable.

 

Ok, if you think there is no way the 41 mm offset would work then I I’ll just get them at 18x9.5 +17 then. I was just trying to make sure they won’t stick out too far is what I was trying to do, especially on the front since I haven’t seen anyone use the real zr1 wheels all around. Do you think I should try them at 41 first and just see how it fits like I mentioned or just go ahead and get them so it would be 18x11 at 36 offset? I would be using the 305/35 tires, I already ordered one of them so I could have checked the fitment when I placed the order with the wheels. Let me know whichever way you think I should do it. Ill probably call them back to place the new order tomorrow and I’ll just get all four wheels this time. I messaged someone on here who had 17x11.5 wheels on an 87 to check what offset they were and he said it was 34 offset and the car was lowered so getting them like you mentioned would probably work since that must not be past the fenders.

 

The operative word there is "think." Again, I haven't done any of this with an early C4 myself, so I'm referencing other people's efforts as well as the difference in offset for the factory 16x9.5 wheels (early C4s) vs 17x9.5 (later C4s). The "Big Doggie" mod to narrow a later C4's rear track and fit ZR1 rear wheels (17x11 et36) narrows the rear end 14mm, suggesting that the early C4's have a 14mm narrower track (because a ZR1 wheel seems to fit them). OTOH, the factory 16x9.5 et38 have 18mm less offset than the factory 17x9.5. I know that an 11" wheel with 50mm offset and a 315 tire fits a later C4 properly. Based on that info, it seems to me that you want a final offset of somewhere between 32-36mm for an 11" wheel. I haven't seen anyone attempt more offset than 36mm, but that doesn't mean nobody has (i.e. I haven't seen it all). I forgot you are planning to use those taller tires, which makes it even more important not to poke out. If I were doing this project, I'd probably start with 17mm and end up at 36mm. But with all the money you will put into this project, it would be wise to beg/borrow/steal one ZR1 wheel (11" et36) with a 315 tire (I doubt you'll find anyone else who has mounted a 305/35) to test fit. It would be a lot easier to beg/borrow/steal a 11" et50 wheel with a 315 tire mounted. If you do that, you can use 14mm of spacers or washers to carefully mount and measure the clearances.

 

I see what you mean about borrowing a wheel to test fit. The only problem is that I live in a smaller town and I have hardly seen any c4s before, there’s two that hardly ever comes out. And I don’t think I have ever seen a c4 zr1 in person. I guess what I will do just to be safe is get two of them 18x11 +36 offset and then if those fit I’ll order the other two. This way if the front is a bit too far out I can order the next two with more offset, or less if the rear rubs on the inside and I’ll use the 36mm as the front. Weldcraft said they are out 7-8 weeks on new orders so it will take a while before I get them but it’s safer to do it this way in case the front sticks out to far. Like you said these should work for the rear almost certainly because I’ve heard a lot of people say they use the real zr1 wheels for the rear, I’ve just never heard of using them in the front.

 

OP - Where are you actually located? I'd think a 'borrow' of an 11" @ 36 with a 315/17 NOT out of the question. The ship of 'one' wouldn't be out of the question either and substantially less $$$ than your recent thoughts. You speak as $$$ don't matter - it always matters! Weldcraft's work is outstanding. You let Weldcraft do the 'math'

 

I’m in Kenton, Ohio. It’s the Midwest part of Ohio. If you know of someone near me with zr1 wheels then I would be happy to check the fitment with them. I did not mean the price doesn’t matter, I just want to get the wheels just how I want them in the first place so I don’t regret it and end up spending more to get another set of wheels later. I did something similar to that with the headers I put on the car, at first I bought a cheap set of stainless headers and paid a shop a lot to install them and then they ended up hanging down so low that any bump hit them. Then I had to buy a set of Hedman headers that actually fit so I installed those. This ended up costing a lot more than if I just bought one of the headers that were known to fit in the first place because the shop spent a lot of time modifying the stainless headers to work and they still didn’t. The reason I planned on getting two of them is because a lot of people use the zr1 36mm wheels for the rear so those would work for that part and then I could just check the front fitment with those. I ordered one tire earlier and it’s supposed to be here on Monday.

 

17x11x36mm is a know fit for 84-87 C4's. I have seen many over the years with them on front and rear. 18" would be the same as long as the final OD doesn't get too large.

I don't remember who's car this was. Here is a picture I had saved from more that 20 years ago. He had 90 model ZR1 wheels on all four.

 

ok, thanks for posting that. I was actually just about to ask you something. You said earlier you had 17x10.5 wheels at 44 offset, this was on an early c4 right? I got to thinking if those work then I would probably just be able to get my wheels in 18x11 at 41 offset since they would only sit 3mm further to the inside. At most they would need a 5 mm spacer on the rear and you said that would work on the stock studs wouldn’t it Matthew?

 

Yes, my car is an '86. the wheels are 17x10.5x44mm

 

If you can get the wheels you like in 18x11 et41, I would do that and then plan to use spacers to get them just right. Yes, 5mm spacers will net you 36mm offset and should be safe with stock studs. You would want to get 6 turns of the lug nut to be safe (really 5 turns is safe for a 12mm stud, but a little extra margin is good). You can check this now: how many turns of a lug nut do you get with your current wheels and no spacers? Since thread pitch is 1.5mm/turn, if you can get 8-1/3 turns of the lug nuts without spacers, then adding 5mm spacers will still allow 6 turns. And even if you have to replace all your wheels studs with longer ones, that is still way cheaper than widening even one wheel. It's a no-brainer.

 

Will FIT is very different from a 'comfortable/practical' fit.

 

also I have used these ET style lugs nut to grab a few extra threads when needed. the diameter of the shank has fit any aftermarket wheel that I have checked. its a standard size.

 

Yes, good point. Even the Vorshlag open lug nuts grab about one extra thread compared to regular lug nuts, although they aren't true ET style.

 

I didn’t mean that the wheels can come in 18x11, they have a standard size of 18x9.5 at +22 and I would have to add 1.5” to make it that size. At that offset each wheel is about $10 cheaper and I figured it’s better to have more offset than not enough so getting them at that offset would probably be better than making them 18x11 +36. With my tires being 305 instead of 315 maybe they would fit without any spacers at all with that offset too.

 

ok, what size tires do you use and do they rub at all? Getting the 18x11 wheels at 41 offset like I mentioned would only move the wheel in just over 3mm so I’m thinking they will fit and be sure not to stick out of the fenders this way.

 

Okay, gotcha. All of this reasoning seems sound. I predict you will still need spacers, but again no more than 5mm and maybe even less.

 

all four are 285/40-17 but they are goodyear GSD3's which run wide, probably a 1/2" wider that most 285's

 

my next set of tires will be Nitto 315/35's 555G2's on these same rims, all four.

 

With a section width of 11.3", those Goodyears are exactly 1" narrower than the Toyos he wants to use. They are also 0.4" shorter in diameter. So those are pretty significant differences. The 315s you plan to use next will be wider but almost 1" shorter. He's going to have to get net offset right on the money to make everything fit properly because the tire height combined with significant width will combine to make it pretty critical. Not impossible by any means, but there won't be much margin for error.

 

Well I guess since the offset needs to be just right then it makes since to get them with a bit more offset than what I should need that way it can be fixed with spacers if needed. I think I will go ahead and order all four wheels as 18x9.5 +22 and then see if they will need spacers when I pick them up after they are widened.