The 4x4 Rallyes are 15x8. A 225/75/15 is about as small as one would want to go, as anything smaller tends to be stretched out too much. Most of the original trucks with that wheel used one of the following sizes, 10.00-15, 31x10.50x15, 235/75/15.
If you're happy with how the 235/75/15s perform, there will be no problem using them on the Rallyes. The 31x9.50x15 also works very well on them. That is the size I'm running on mine.
Joker, alot of the issue with tire to rim sizing invilves proper sidewall support. General rule of thimb is that you have a rim that's approximatly 1"-2" narrower than the section width of the tire. Example, a 10" section width tire would run on an 8" rim. Improper sidewall support can lead to erratic handling and/or premature tire failure. Another case in point, I mounted a set of 31x10.50x15s on a Jeep using the stock 6" wheels. I did warn the owner that they would be too narrow, and that there would be handling issues, but she wanted them anyway. A few days later, she came back with a severe wandering complaint. I drove it, for sure, it was all over the palce. We ordered a set of 15x8 wheels, installed them with the same tires, drove like new afterward. In fact, it actually drove better than it did with the stock 205/75/15 tires, as the wider tires provided better stability.
