Have you researched for images of 17s on Darts?
Or ride quality with HD suspension, and low-profile tires?
Can you guarantee that you will never drop a corner into pothole,or curb it hard enough to destroy the rim and or tire? Is there room in your budget for a spare wheel?
It is a given that Darts will have trouble in fitment of a lot of off-the-shelf combos.My rear solution, was to obtain the wheel that I liked, and make it fit. The wheel was a common 4.5 BS.First I had to move the springs in-board to get them out of the way. Then I had to narrow the rear to center the assembled wheel/tire combo.I did this for the widest tire that would fit without tubbing. Now I can fit anything in there up to that largest size. I fit 325/50-15s into a 68 Barracuda at nearly 2 inches lowered. IIRC this tire on a 10" rim is around 13.2 section width.
I know your Dart has a smaller wheelhouse, but the idea is the same.Embrace the spring moving, and the narrowing; it's not a big expense. Especially if you go to a custom bs wheel, and then break one on a curb. It sucks to wait all summer for another one, and get hosed on the price,again.
Here is the tire manufacturers formula for determining the tire size.They design a tire for say, an 8 inch rim. They mount it up and measure the section width. Their design criteria is that the wheel size is 70% of the section width.So 8inches divide by .7 is a target section width of 11.4 inches or 290mm. The tire would then be branded to the nearest 5mm, in this case 285 or 295; depending on where it exactly fell.IMO this is more or less nonsense. Who in their right mind would mount a 295 on an 8 inch rim.The tire pressure to run the tread flat on the ground would be so low that the handling would be ridiculous. I don't know why they do it that way. They call that 8 inch wheel, the checking width. It basically means that the tire's section width, when mounted on the checking width wheel, will be the same/near the same, as branded.
IMO, the wheel width should be the same as whatever the tread measures.This is how we did it before radials.This is a bit harder to determine with modern radials.
So here s how I skin this cat.....
I use 8 inches for a 245 section width as a standard; and add/subtract an inch for every 25mm of section;rounded to the nearest available size.(25mm being about an inch)
Example; 245 (is 9.65inches, and 9.65 x .85 = 8.2;) rounds to 8",the standard
Example; 325-245 =80mm difference. 80/25=3.2; plus 8 =11.2, rounds to 12
Example; 295-245 =50mm difference. 50/25=2.0; plus 8 =10,.... rounds to 10
Example; 205-245 = -40mm difference. -40/25= -1.6; plus 8 =6.4, rounds to 6
Example; 185-245 = -60mm difference. -60/25= -2.4; plus 8 =5.6; rounds to 6
You can see that the formula doesn't quite work right on the smaller sizes, so some common sense is required,but really; who buys 185s?
There is nothing stopping you from mounting your tires on other wheel sizes, but keep in mind the following;
The correct tire pressure is the pressure at which the tire runs flat to the pavement.
If the tire does not run flat it will wear out prematurely
If the wheel is too from correct it may be hard to mount, and may be hard to run with a correct tire pressure.
If the correct tire pressure is too low, it will handle like crap.
If the correct pressure ends up too high, it will ride like crap.
A target range of tire pressure is 28 to 32,for a street-A; the lower for ride, and the higher for handling and fuel mileage.
