I am by no means whatsoever a tire guru but I think it's going to take new wheels.
The wheel width / diameter is significantly different between the two and even if that were not the case the wheels that come with the R1's are two piece design with adjustable wheel track whereas the Turf & Industrial wheels are 1 piece and not adjustable.
I would talk to a local tire shop (esp if you have one that does a lot of tractor work) and see if they can find something to fit your existing wheels (there are companies that are starting to come out with a R1/R4 hybrid tire like the Goodyear R14).
Perhaps a cheaper alternative would be finding chains to fit your R4's
Thanks very much. I'm checking into the R14T's. They make them in the CK35 sizes: 27X8.5-15 & 15-19.5 so it is just a matter of finding them and pricing them out.
Just get some of these chains. Use them all winter and when I am logging in the summer and never get stuck. Are your tires loaded it can make a huge difference.