You MUST stay with the 25" series tire and staying with the same manufacturer is also very important. As you noticed different manufacturers measure differently for some BIZZAR reason. If I can figure out how to attach pictures on this forum I'll put up some pic's of a 2004 Honda TRX400AT with a new set of Bearclaws 25x8x12 Front and 25-10x11 Rear.

 

^--- a little late

.. but on to waht you say.. stay with the same manugature?...
who the heck cares.. its one inch.. its a TIRE!..
get all four different tires.. doesnt matter.. get waht ever you want.. 23"?
how bout un mount the tires.. and measure from lug to the ourther lug on the opposite side of the tire.. maby the weight of the quad is making the tire looks smaller.......