The best thing, is to start with a base comparison of the tires you have. If you could provide the manufacture, then we can research the tire data in the web sites I noted before, or find the correct manufacturer.
Ok, now for the Ag tires you mention. That particular ag tire uses a much larger diameter rim than the turf's. It will have a fairly short sidewall, and has a somewhat narrow tread. You can probably get an Ag tire that runs on a 16" rim; It will have a big sidewall, will be a wider tread, and be more "balloony" for lack of a better word. The front Ag's are a bit wider than the turf, and do use a slightly larger diameter rim.
The turf tires now, they are more balloony. They are a floatation tire, and tend to be wider than Ag or R4 tires. They sperad the weight over a larger surface area, so there is less impact on grass. In the case of my Kubota, I use 16" rims for both turf and R4. But, the rim for the Turf is wider, because the tire is wider and needs the wider rim to properly support the bead and sidewall.
The important thing is that each tire is ratio matched to the gearing of your tractor. Unlike a 4x4 pickup, which uses the same size tire, and same gear ratio front and rear, the tractor uses a different size tire fron and rear. To adjust the geartrain, they have different differential gearing front and rear. The rolling diameter of the tire has to match with the gearing of the tractor, or else you will overload the axles and driveline and it will break.
So...
Your 14.9-26 rear ag tire uses a 26" rim, recomended width of 13". It has an overall tire width of 14.9". Overall diameter is 52". See
http://www.firestoneag.com/tiredata/bias/rtr_tfr.asp
I tried to look up the front tire size at Firestone, but did not see a front ag.
I'll see if I can look the other tire sizes up later, or you can look. Between the Firestone and Goodyear sites you should be able to find the proper size tires and spec. I have to do a report for school... so I will look later....
