68 dart GTS 18 rims question

In the front the Pirate Jack kit is the same as a 73+ disk set up. If you're using the 5x4.5" kit it's identical to stock, the adaptors let you use the 73+ spindles which is what is in that kit.

In the back the rear disks add the thickness of the rotor. It usually works out to be about 3/16" per side compared to drums. Are you using BBP axles, or did you re-drill the small bolt pattern axles?

The limiting factor for width is going to be the in the back with the stock spring locations and wheel tubs. For a '69 the widest you'll probably manage without cutting or rolling the quarter lips is a 245. You can easily fit a 245 up front, in fact with a 18" rim you can fit a 275 up front. But since you probably don't want to run larger tires up front than out back you can run 245's if you want.

In the front with an 18x8 you could run 5.25" up to about 6" of backspace and have it work with a 245/40/18. Now, that's +20 to +35 of offset, so if you want to run a narrower tire just run whatever rim you width you need with and keep the offset between +20 to +35, it'll fit. Same goes for a 18x8.5.

In the back, assuming you have BBP axles (not redrilled SBP), you'd be looking for an 18x8 with about 5.25" to 5.5" of backspace to run a 245. The 67-69 cars tend to be tighter to the quarters, so I'd be looking for closer to 5.5" and being able to run a small spacer if need be (vs being too close to the quarters). If you go more than 5.5" you'll need a spacer to get you back to at least 5.5". For example, if you found an 18x8 with 5.7" of backspace, you'd likely need a 1/4" spacer to pull that off. Same goes for the 18x8.5's, they'd work if you keep the offset around +20 to +25-ish.

You can see the overlap, if you wanted to run 245's on 18x8's and be able to rotate you'd want 5.25" to 5.5" of backspace. Now, that's an estimate, you should still measure your car, especially in the back. The front will work fine either way, but on a 67-69 cars there isn't always a lot of room.

Also, the same works for a 17x8 with a 245/45/17, 5.25" to 5.5" backspace. In the front you'd be a little more limited, because the outer tie rod end usually starts to interfere with most 17" rims around the 5.6" backspace mark. But to run square on a Dart with the stock spring locations it's basically is the same for 17's or 18's. There's the 17x8" replica Bullit wheels for mustangs that are usually pretty affordable, they have a 5.680" backspace which would probably take a 1/8" spacer front and rear. And in the front those usually require a little hub bore modification to clear the hub snout on the Mopar 73+ rotors.

Some options...Wheels - 5 x 4 1/2 in. Wheel Bolt Pattern (app)