Thanks for the link. It looks like 14.9x28 R1 is 54.1" diameter, while the 16.9x24" R4 is 50.1. A 3.5" difference.
Probably not much difference in clearance by the time you divide the difference in two, and figure for the extra amount the R1's will sink into the gound with fewer bars. It will just come down to better traction I guess.
Thanks again.