Re: Different size tires?
Conventional wisdom would say: Don't do it! and it is not recommended for autos--in fact I think here in PA, both tires on the same automobile axle must be the same size otherwise the car fails inspection. Auto spares though, are almost universally the small space saver tires and although claimed only good for 50 miles or so at less than 50 MPH, they are still accepted equipment.
HOWEVER: 10 cm is only about 1/2 inch difference in cross section and probably about the same in diameter. (roughly 25.4 cm=1 inch). There is no differential on a boat trailer axle so no gears to be constantly turning--I doubt that you would get into trouble as long as the load rating was enough to carry the expected weight..
In fact, I just replaced my 4.80 X 8 tires. The old ones were cracking and were two different brands---LO---To my surprise The two different brands were about 1 inch different diameter. No wonder the trailer looked crooked.