Can I mount Turf tires on R4 rims? They are the same size.
If the rim diameter is the same and the section width of the R4 tires is close to the same section width of the turf tire then yes you can, I went the opposite direction and put R4 tires on the back of my B5100E, I replaced the original turf tires that were on it.
I was able to find R4 tires that were close enough to the same section width as the turf tires I replaced, Finding a turf tire with the same or close to the same section width as your R4 should be a little easier because there are a lot more turf tire sizes than there are R4 sizes, You did not mention what tractor you had, many of these smaller tractors can use implement tires and even car and light truck tires, When I needed new turf tires for the back of my B7500HST i replaced the Goodyear clover tread tires with a set of LT Snow/all terrain tires, the rim/section width and height were the same and they were about 1/3 the price.
Just keep in mind that if your tractor is 4wd then you also have to keep the height the same(within 1/2" difference)
If you are changing tires now would be the tire to add ballast to your tires, I chose windshied wiper antifreeze to use as ballast because it was less expensive and less corrosive than calcium chloride and just less expensive than beet juice. I bought the -20 degree windshield wiper washer fluid on sale at places like Walmart and TSC, If you don't live in an area where you get freezing temps then you can use a washer fluid that has a higher freezing temp, I live in NJ so I went with the -20 wiper fluid
You will need a valve stem attachment for adding the antifreeze ballast, Using ballast in the tires reduces the amount of add on weights you need to hang on your frame.
On my tires I mounted the tires and seated the beads with air pressure, I then put a ratchet strap around the tire and let air out as I tightened the strap, I laid the tire flat with the valve stem facing up and added the ballast, I forget how much I put in each tire but at 8Lbs per gallon 10 gallons of fluid will add 80lbs of ballast to each tire so the more the better.