The car I got came with 18x9 rears and 17x8 fronts. The tires seem a little small being that the fronts are 225/45r17 and rear is 245/45r18.

Would a 295/45-18 and 255/45-17 fit in the fenders? The 295 is a little over 28" tall and the 255 is 26"

Also the rear looks 1 or 2 inches lower than stock because of the springs

My 70 Charger has an 18x9 front with a 275-40-18 tire. The rear is an 18x10 with a 295-45-18. Plenty of clearance and I have my car a bit lower than stock height.

Don't go by this as a gauge as to what will fit a 68 Plymouth B body rear , the charger has a huge rear wheel well compared to the Plymout.

Front , I'm not sure if the fronts have more room on the Charger ???

Are the inner and outer wheel houses the same in all the 68-70 b body cars? If so, I'd say that you may luck out. I'm not sure if the wheel opening arch is higher in the Charger, it might be. If so, that might pose a problem. Any chance of borrowing a used tire from a tire dealer? You could mock it up in the wheelwell to see. I just had new Nittos mounted and my old 555s were kept here merely for mock ups for future car projects.

I've seen some people run a225/50r17 or a 245/45r17 in the front of a 68 roadrunner with a 8 inch wide wheel. On my rears I have plenty of space to go a little bigger and wider. I have a 18x9 on the rear with a 245/45. I just want a little more side wall on both.

No they are not. Dodges have more room in the rear than Plymouths.

I've got 295/55-15 tires on the rear of my '68. They fit, but just barely.

Thank you. I'm glad to learn this.

If 68 and 70 are similar I have 30" (275-60-17) on the back of mine. I moved the springs back some but anything that says its 29" or less should fit as long as the section width isn't too wide.