I like to look at it this way: the diameter or height of the stock 235/75-15" is 28.9" and the Astro van tire is 27.7" in Diam. That difference is the important factor in affecting the 4WD operation and the speedometer reading the correct speed. There are many 'tire size calculartors' on the net. One of the best is the Miata.com site and there is on on the Tacoma site as well. Here's another one to look at: https://tiresize.com/calculator/ I like the Miata one because it is easy to look at the stock and the 'optional tire' side by side.

 

Ahh ok I feel like a dumb dumb. I had no idea the 'wider' the tire is the thicker the side wall becomes whitch changes your tire height... I wonder if you can just make up for that little bit of difference from airing down the back tires a few psi lower then the front ones to make up for it? I guess it would be the same deal if you had all 4 of the same tires and width but you have more tread worn down on one of them then the other 3.

 

As long as the circumference is the same, it would be fine...good luck with that


Exactly. All 4 tires on 4WD vehicles need to have the same circumference. If you want to avoid issues with the drive train, it's always best to replace all 4 tires at the same time.