Ok, so there's a few things going on here. First off, I do believe that he's running 18x10 with a +25 or +24mm offset with 315/30/18's. But there's some factors that play into this as to why this works on his car, where I would tell you that a 275/35/18 is about as wide as you want to go on a Duster if you don't want to cut stuff or move the springs.
First off, his car is cut. That makes a big difference. If you don't want to cut anything, you're much more limited. If you're willing to cut, roll, and "push" some sheet metal around you can add a TON of space, especially on a Duster. Second, it says right in the article "minimal rubbing". How "minimal" that is of course it up for interpretation. If you're willing to rub, you can add 10mm to the tire width easily compared to what won't rub at all. So, if 275/35/18 fits without rubbing, figure you can go at least 285 with truly minimal rubbing. I suspect his car rubs more than what I would consider "minimal", but that's just my opinion. Track car vs street car makes a huge difference too. What doesn't rub on the track might rub on the street, you tend to see a lot more stuff that would cause issues on the street. And finally in the general category- a 315/30/18 is supposed to be on a 10.5 wide wheel, minimum. Which means those tires are squeezed onto those rims a little, so, they're not as wide as the factory specs would suggest. He's probably losing a 1/2" of width to the smaller rims.
In the back-
Rear quarters have had a TON of work done to them. It does appear that his shackles are in the stock location, no offset or relocation. It's hard to tell, there are no pictures of the full shackles so it is possible there's a 1/2" offset in there. Definitely no 3" relocation. But, he totally tubbed the rear of the car. That adds over an inch to the outside compared to a stock Duster. It also adds to the inside clearance, even with the stock spring locations. You can see his tubs here-
View attachment 1715718970
You can also see his tire clearance to the springs. This is
REALLY tight for the street.
View attachment 1715718972
In the front-
Two really big things to consider for the front. First off, it says he's using the original spindles with a Wilwood conversion. That means he's using SBP spindles, and the newer dynalite conversion doesn't increase the track width. So right off the back I would say that if you're running BBP disk spindles you'd need to at +10mm to the offset. That puts you at +35mm, which is what I'm running on my 18x9's with 275/35/18's. So that's not a mystery, the SBP vs BBP spindles change the front track width substantially. The second thing you can see here...
View attachment 1715718971
Look at how much negative camber is on those wheels!!! That has to be at least -2°, if not -3°. I run my car at -1.1°, which is visible, but not anything like this. That changes the fender clearance a lot. The other thing is that he cut his fenders, so, another 1/2" of clearance there compared to stock.
That's the problem with pulling specs from other people's cars, you have to know everything they did to use those specs. You have to know what spindles, brakes, and axles are being used. In this case, if you're using BBP spindles and 73+ disk brakes, your 18x10's should be closer to +35mm of offset. Even with that, I would still recommend 275/35/18's unless you want to really start cutting, rolling and pushing the fenders. If you do all of that I still wouldn't recommend the 315/30/18's, they're supposed to be on 18x10.5's or better. 295/35/18's would be a much better bet, but they're still gonna take a bunch of work for a street car. In the back, 18x10's will fit with the stock spring locations and no cutting. But not with 315/30/18's. I was running 295/35/18's on my Duster with a 1/2" spring offset and another 1/2" trimmed off the quarter lip, and those were tight. I've since done a "reverse mini tub", which makes the outer tub flush with the quarter lip. Doing that I can see how you might be able to fit 315's. But without it, nope. Backspace will depend on your axle housing, axles and brakes. The 6-link will buy you a little space to the axles because of the width of the links vs springs, but you're still using the stock perches. So probably similar clearance to a 1/2" spring offset like I have.
