Great, insightful comments so far.
If you are set on having two sets of wheels & tires, get turfs and ag tires. R4's on a CUT are just a compromise effort. R4's and turfs are too much alike to have both.
Good point. I hadn't thought about how R4s are already a compromise. I was originally just going to go with R4s but I got the idea for a second set of tires from a thread here (somewhere, I can't find it now).
However, I also think changing them back and forth will grow old in short order and more often than not find yourself wanting the opposite set on the tractor that you want at the time.
I was concerned about that as well, but I guess it depends on just how big and heavy the tires will be.
I'm currently shopping for a new tractor. I'll save the details for another thread, but suffice it to say for right now the decision is between a Kubota B3350HSDC and a LS XR4140HC. The Kubota uses 7-12 fronts and 12.4-16 rears and weights 2,447lbs, while the LS uses 12-16.5 fronts and 17.5L-24 rears (R4s) and weights 4,446lbs. A noticeable difference in tire sizes and weights between the two, which in turn may affect my tire decision.
I also need to sit down and really think about just how often I would need each tire type throughout the year.
The simple solution is don't get on the ground with your tractor when the soil is wet and then it wont matter what tire you have on it.
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If you plan to use your tractor at all in muddy conditions, like down by your creek, then go for R1 tires. On dry ground with a CUT they don't damage your lawn any more than the R4 but if the ground is a bit soft, expect to leave the bar tread marks but they don't usually spin and tear out a divot like the R4 tires do.
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I guess that your choice of tires boils down to what you will be doing with your tractor the most. If it is mowing your yard, then R4 tires are your choice. Then the occasional foray into the woods and soft soil may not be too much of an issue.
One final consideration for you though: Do you have a second tractor available to pull you out if you get stuck in the soft ground? If not then you may want to consider R1 tires. I have pulled my brother in law (R4 tires)out several times when his tractor got stuck in soft spots. Had to pull my back hoe out a couple times also when it went down in soft soil although one of the times it was at the edge of my pond and any tractor would have been stuck in the quicksand like soil.
Finally, I prefer a dedicated lawnmower (ZTR in my case) for lawn mowing and a tractor for heavy stuff, so the only time my tractors go thru my grass area is when it is getting to the back pasture stuff for bush hogging or hauling off debris in the FEL.
Unfortunately Mother Nature has her own plans, which often don't align with my outdoor activities.
Getting stuck near/in the creek was the original reason I wanted R4s, but I know first hand they may not always save you. I had rented a Bobcat skidsteer a few years back and broke the bead of a tire while working in the creek, which caused an instant flat. The rental company had to come out with a mini-excavator to help change the tire. While I wish I had a mini-excavator lying around for just such an emergency, I'd end up driving my Jeep into the pasture and use it to pull the tractor out. I am a little concerned about R1s tearing up the creek bank though. The horses do enough of that on their own, I wouldn't want to compound the problem.
I currently use a garden tractor to mow the lawn. The tractor will be used for maintaining the pastures and work around the barn. Once again, the horses do too good of a job compacting the pasture soil so I don't want to contribute to that problem with the wrong tires. Once the garden tractor dies I'll probably replace it with a zero turn mower.