I recently bought a 1970 or 71 MTD 960 and decided that I wanted F2 front tires on it. This took me round and round the internet, searching for options. Maybe I can save somebody some time by posting this.
The tractor came with 16x6.50-8 tires on 5-3/8" three lug rims.
The F2 tires that I found to fit a rim that wide are expensive. Firestone has the only affordable F2 that wide. The center rib on the Firestone is too wide and stands out too tall for my liking. They are also $85 each.
Deestone has 3.50-8 and 4.00-8 F2 tires that can be had for $25 each. The proportions look better to me. They are tube tires, so it is possible to put them on 5-3/8" rims. I don't think it's really a good idea to push the rim width like that when I'm going to be driving over logs and stumps.
So, narrower rims. Turns out that's not so easy with a 3 on 3-1/2" lug bolt pattern. I looked and looked and mostly came up with wide wheels for racing go-karts.
There are two reasonable options.
Go to a narrow integrated wheel/hub from an older garden tractor or buy new 3-3/4" x 8" wheels from Martin wheel for $70 a pair, or
Find some narrow Snapper Snowblower three lug rims.
I wanted to keep the hubs, so I found some Snapper narrow rims for $60 shipped on Ebay. Where I live I'm not going to find snowblower parts in a salvage yard.
In keeping the hubs I'm also not going to have to be concerned with properly spacing out narrower integrated hubs. (In case you are new to steering geometry, the kingpin should point right at the center of the contact patch on the tire.)
So there are the options for tri-rib tires as of October 2020.