Are you running the stock leaf springs ? I wanted the 15X8's but there just isn't enough room. I really won't know how much room I have until my spring hangers get here and I get it together I also have air shocks so I can get a little more out of it. I'm hoping the springs will raise it almost to the top of the tire which should give me the clearance I need.
Air shocks are a terrible idea. All they do is trash your shock mounts, and compromise the handling of the car. The shock mounts are not supposed to carry the weight of the car, just the load from the shocks as they do their job. Make the shocks stiff enough to raise the car and now they're carrying the weight of the car.
SS springs aren't going to lift the wheel opening above the top of the tire on a Dart. The wheel opening is too low. Not only that, but if you did succeed in raising the car that high, you would either have a crazy front to rear rake, or your car would look like a 4x4. If you really want to run those tires, order a rim with a custom backspace and do it right. Or shorten the axle, whatever floats your boat. Jacking the back of the car up will just make it handle and ride like crap.
@cpearce You mind telling us why you wouldn't want to put a 245 or a 255 on an 8" wheel?
Considering the minimum recommended wheel width for a 255 is 8" (max 9.5) and for a 245 it runs from a minimum 7" to a max 8.5", you must know something the engineering world does not?
The minimum wheel width listed for a 255/60/15 is 7" for both the BFG T/A's and the Cooper Cobra's
What is the point of putting a wider tire on a car if you are going to mount it on a narrower wheel to suck the sidewalls in, round the tread area just so it the same width a narrower tire mounted functionally and properly? Just to say you run wider tires?
I get that section width grows as you increase wheel width. So does the contact area. So a smaller width tire actually looks bigger. Again, wide tire on a skinny rim seems like an ego move to me but...
As long as you're within the manufacturer's specifications, I don't see how this matters. Every tire lists a rim width range, the acceptable tolerance on the width of the rim. They also list a "measured rim width", which is the width of the rim that was used for the specifications listed by the manufacturer. For a 255/60/15 the measured rim width used is only 7.5". So really, putting them on a 15x7 isn't changing a whole lot. You're still going to put down the same tread width, you might have to run a slightly lower tire pressure to do it. You might squeeze the section width a little, but it's not much. Now, if you need that last .1" of clearance like the OP is going to, it could make a difference. But if you stay within that manufacturer range you're only talking about a few tenths of difference in the measurements compared to the published specs.
Sidewalls flex. Whether your run the maximum or minimum rim width changes the shape of the sidewall some, the tread maybe a little, and that can be controlled some by tire pressure. If you stay within the manufacturers specs you're within the acceptable performance for the tire. Does that change? Sure. AutoX and road race types like to run closer to the maximum rim width, it limits sidewall flex a little bit. Drag racers might want closer to the minimum, that sidewall flex can help and you just adjust air pressure to get the contact patch right. On the street I like to run between the minimum to measured rim width, not at the maximum rim width. Why? Because it gives me some sidewall bulge to protect my rims from curbs and potholes. Might get a little more flex out of the sidewalls, but on my 18's that's less of a concern anyway.
Now, if you start going below the minimum width or above the maximum that's a different story.
