Why are the S 800 tires different size front/rear

Like the title states why do the early rzr S have a stock 26×9 and 26×12 setup vs 4 of the same size. The newer machines all seem to be the same tires all around as far as I know.
Wondering if it was a performance thing on just the way the 800 was built or an old trend that polaris simply phased out.