380/85-34 tires on One-Eighty

you know that 380 mm is about 14.9 inches wide... Most who change go to the 16.9 or 18.4 inch

These days if I want to swap sizes (or even if I just need new rims) I now find rims & centres for the tire size I want, regardless of the bolt pattern and centre hole. I then get a disc cut on a plasma-table with the right bolt and centre hole pattern, and make it out of steel the same thickness as the new centres. I cut out the old centres, grind a good bevel for a weld prep on my adapter discs, and weld the new discs in. If you're a reasonable welder and take your time grinding smooth they'll look stock once you're finished. Doing it this way gives you complete flexibility to work with any rim/tire size you want. Here's a picture of my 180 after I converted to 18.4-30 and the adapter discs I used. These rims aren't adjustable and I know it's not proper Allis paint, but the rims and tires only cost $400 and the adapter discs were only about $200 to have made, so I think it's still a pretty good looking set of tires & rims for only a few hundred dollars.

This discussion actually comes up on here pretty frequently, and Dr. Allis always correctly points out that the 18.4-28's have a very respectable contact patch area. There's not anything substantial to be gained by going from 28's to 30's, and you actually lose contact patch by going to 16.9-38's like so many folks want to. But I think the desire to change tire sizes is very seldom driven by the desire to get more contact area. In many cases (like mine) it's the owner wanting to change to a more standard tire size (around here you can find used 18.4-30's in great condition everywhere, and I have several sitting around because three other tractors of mine take them). Sometimes it's done for row-cropping reasons like you want, and sometimes it's done to improve the look of the tractor: Folks may disagree, but I always thought the 170 and 180 especially looked a little too saggy with the original 28's - especially when they started to wear down. The 30's only have a radius increase of 1.5" (depending on brand), but it seems to make a heck of a difference in how these tractors look. With the slightly taller tires they look like a mean, aggressive tractor ready to go attack the land. There are a couple pictures floating around on here of someone who's put 16.9-38's on their 180 and 170. I wouldn't want to go that narrow on mine, but I have to admit they look superb.