The back ought to be OK... I'd still be careful on the front...

 

Peter, I'm a dork. Sorry...I shoulda clarified that I'm using spacers/adapters on the rears ONLY. For the fronts, I'm simply moving the 18 X 10s (+41 offset) I have in the rear right now, up to the front. No adapters, nada. Just move the rears to the front.

IIRC, for a 10" wheel up front, you need a +50 offset (I remember from Rynberg's post: https://www.rx7club.com/showpost.php...61&postcount=8). So lets see if I learned anything. Right now I have 18 X 8.5s up front in a 37 offset (stupid SSR offsets). A 10" wheel is 1.5" wider, which is 3/4" on each side. So the 10" wheel will sit further out another 3/4", or 19mm. Add to that that the 10" wheel is a 41 offset (not a 37 offset like the 8.5s), so I'd be at 19 - 4 = 15mm sticking out. On stock fenders, I'm pretty sure that won't clear the fender. But with an additional 20mm to spare (wide front fenders), I should be good. (I'll have 5mm to spare, to be exact).

~Ramy (KNOWING he made a mistake somewhere lol)

 

Right, you'll have plenty of room on the inside, I should have brought that up. From experience, I know that an 18x10 +44 with 285/30/18 has plenty of room on the inside with the stock suspension peices (the trailing arms being the biggest worry). It's been a number of years since I had that combo in the rear, but IIRC about 1" clearance with the stock trailing arms. While the 18x11.5 would have and extra 1.75" (32mm) added to the inside (as well as 1.75" (32mm) to the outside of course), the -2 offset would shift the centerline of the wheel 46mm (or actually 47mm - remember, ' 0 ' counts as a digit) outward, easily making up for the gain of 32mm of lip on the inside.

+44 offset means there is 44mm between the wheel hub face and the imaginary center line of the wheel, with the wheel hub face sitting on the outboard side of the imaginary center line. With the -2 offset, the wheel hub face is shifted inboard, past the imaginary center line, 2mm into negative territory, netting a total shift of 46mm (or, again, actually 47mm). So, an 18x11.5 -2 would actually have 14 or 15mm more clearance on the inboard side (46 or 47mm - 32mm) then an 18x10 +44

I have to point out, though, that a 10" or 11.5" (or whatever) nominal width is actually the measurement from bead seat to bead seat of the wheel (where the bead of the tire rests when mounted). The actual width (lip edge to lip edge) is wider, and can vary from brand to brand. There are no standards to how much lip you have beyond the bead seat as far as I know. In other words, one wheel may have less clearance compared to another, depending on how wide it is beyond the nominal width. In reality, I doubt there is much more then a few mm differnence at most. It's only a concern if you are trying to scrape by on a couple mm's of clearance.

This is where I made my mistake. I completely forgot that I was using a 16x8 +35 as a baseline, not the stock 16x8 +50. The former would push the wheel outboard 15mm, making it a bit more flush then the stock wheel. I've said before that you cannot talk about offsets without talking about the relative width of the wheel, and I'm guilty, in a way, of violating this. I wanted you to ignore wheels widths (so I left out references to the width in the beginning) but ended up confusing myself, and forgetting what baseline we started with when I began my thoughts in that last paragraph of mine.

Going from a -2 offset to a +23, wheel widths being the same, would shift the wheel inward. Sloppy english on my part, along with brain melt down haha! The 0 to +15 offset reference (pulled from your prior post) was a comparision - sorry. It wasn't a conversion, but to show that what we calculated in this thread falls within the same general range that Rishie and I calculated before. I actually came up with 18x11.5 +10, IIRC, in my PMs with you a while back. This was me using 18x10 +44 as a baseline. You can get different numbers based on where you start as a baseline. More on this at the end.

Yes, going from a 0 offset to a +15 offset, wheel widths being the same, the wheel would shift inward.

When I calculate wheels for widebody fenders or flares, I decide on where I want to start (baseline wheel), how I want to get there ( wider wheel widths, spacers), and where I want to end up (how much 'flushness' I want with the new fender/flare, what width does the fender/flare add).

Like going on a trip, you have to start somewhere. I start with wheel spec that I know how it looks with a stock fendered FD. 18x10 +44 is pretty flush with the stock, rear fenders. I've dropped a plumb bob off the side of the stock fenders, and it was near touching the wheel lip and tire side wall. I've seen more aggressive offsets/width combinations on the back of FDs, but this is what i'm comfortable with and where I usually start. If you start with something not as flush as you would like (like the stock 16x8 +50), you have to compensate for it later, adding to the possibilty of a mistake (like I did in the first post).

Having the baseline, I have to decide how much wider I want to go, and how I am going to get there. Is the wheel available in custom offsets in the range that I need, will I have to use a spacer? In your case, you are fixed to a 11.5" width and a +35 offset. You can't get around this, so you have to use a spacer to get you where you want ot be. Assuming the new fenders add exactly 50mm on either side, we now start figuring out how to get there.

Given that we are comparing a 10" wheel to a 11.5" wheel, we can figure that the wider wheel adds .75" (19mm)on either side of the wheel, assuming the same offset (we will work on one thing at a time) So, if we had replaced a 18x10 +44 with a 18x11.5 +44, the wider wheel will stick out more by 19mm). (It will also run into the trailing arm on the inside at this setting, but we ignore this as that we know that we will be shifting the wheel outward).

50mm - 19mm = 31mm. 31mm is the remaining distance we now need to cover to get the same 'flushness'. We can do this by changing the offset from +44 to +13. (looking back at my PMs, the 18x11.5 +10 was based on 18x10 +38 apparently, a more extreme spec that some on the forum have had success with the stock fenders).

The problem is that you have a fixed offset of +35, so you have to use a spacer to reach an effective offset of +13. 35mm - 13mm = 22mm. We can now see that you need to use a 22mm spacer to make a 18x11.5" +35 offset into a 18x11.5" +13. A 25.4mm (1") spacer would make an effective offset of approximately +10, would should be fine.

Now, if you are happy with the 'flushness' of a 18x10 +44, you can stop there. If you want to inset it a bit for a less then flush look, you can tweek the numbers a bit. Moving it inward 10mm would mean using a 12 or 15mm spacer. Given your spacer size limitations though, I don't think this is an option though, short of pressing in longer wheel studs and going with a plain spacer.

Looking over this now, I would say that your could do an effective 0 offset (+35 offset with a 35mm spacer) if you wanted to have a bit more negative camber (to tilt the wheel in a bit), but I don't think it's a good idea with such a wide wheel/tire in back. Going back to my first post, where you end up depends on where you start (as your baseline). I'm looking over the numbers, and they look right, but I don't like the final offset. I honestly don't have the time to figure it out tonight, but I come back to it later in the week.

My recommendation: 18x11.5" +35 with a 25mm (1") spacer, netting an effective 18x11.5" +10.

 

You got it.

Gotta go, be back in the weekend.