tire size.

so I'm just curious here, I have a '90 b2200 and I'm running 15 inch rims for summer but I need new rubber. I have 2 tires at 185/60r15 and 2 at 235/75r15 both pairs with good tread. with an overall diameter difference of 5 inches. if I ran the larger in the back and smaller in the front, would I essentially be throwing my truck away. or would it be ok to drive. Probably wont end up doing it as ill just buy 2 new treads to match the larger of the two pairs.

I currently run 205/70 r15. I used to have 215/65 r15. Both are very similar to stock diameter.

235/75r15 is a pretty big tire. I wouldn't do it. Do much inertia, rolling resistance, and gearing change/speedo error. But, I may be too careful.