Larger tires on a wide frame
 

My 1450 needs some new skins all the way around. I was thinking about running 26x12x12 on the rear and 18.5x8.5x8 on the front . I have 26x12x12 on my 149 and had to shim up the fenders. My main concern is the 18.5 on the front will the larger tires hit anything mule drive , mower deck or the tractor frame

Exactly...everybody always wants to put bigger tires on, and I've never understood why. There really isn't anything to gain, traction-wise or otherwise, and they're just going to cost more anyway.

I picked up these from CL for 100.00 27x9x12 and 27x12x12 almost new. The 27x12's are on the 149 loader and the 9's are going on the 1811. The tires that are on the loader are 25x10x12 atv tires and are loaded. Also I have a set of 25x9x 12 under the round fender 70. All with no lifting of the fenders. The 70 tires are pretty worn but went to a plow day and never got stuck.

By the way the wider and taller the tire the bigger the foot print of the tire to ground contact. When I went from 23x8.5 to 25x10 to 27x12 I noticed the loader didn't dig in as bad. The 23x8.5 where the worst. I dug a hole instantly. I did have duels but it made it way too wide. I just have to load the 27x12 soon with antifreeze.

To answer your question why
Running 26s on the rear speeds up the tractor witch takes away some low end power. Pushing snow on my level drive way the 26s provide better traction. As far as running 18.5s on the front should make the cub set level again for mowing. My 1450 has plenty of down travel for the mower but doesnt have a whole lot of lift so an inch or two of ground clearance will not hurt me any