You'll probably need to change your rims, R4's are generally wider.
If your machine is 4WD or FWA then be careful changing sizes, you'll need to ensure that the inter-axle ratio remains within mfr specs. A good tyre & wheel place should be able to dig up (or calculate) the appropriate sizes and supply rims to suit. If you can provide them with the ratio and tolerance (should be in your book) they'll appreciate it.