Can i mix tire size widths on the front and back?

I have a ford escape 2wd and it has 225/65/15 tires. The backs are worn and the fronts are still really good so its not worth me getting all 4 new. I do want a wider tire and discount tire said i can go up to a 255/70/15. Is it ok to do this? I thought as long as it was the same rim size it was not a problem?|||Sure, you can use different width tires on the front and rear, as long as the two front tires are the same width and the two rear tires are the same width.|||Different front and back are ok, but not different left/right sides