hi,i have 13s on my trailer and i have no trouble at the ramp,in fact i find it easier to see when to stop as i never submerge my axle and bearings.the boat [5m] slides off with no worries.if your using 8s or tens they are much more likely to get wet.of course,some people will just submerge the whole trailer and think nothing of it,i always cringe when i see that.[i'm refering to people with smaller boats here, those with bigger, heavy boats have little choice]. combine that with the fact that the bearings in a smaller wheel have to work harder[as mentioned by angler07] and you have potential problems.9 times out of 10 when i see a trailer broken down at the side of the highway,it'll have smaller wheels.of course the simple solution to this is to repack your bearings more often,but it's a messy job and and if you keep the bearings out of the saltwater,you'll only have to do it a 1/3 as often.bearing buddies and like are a big helpbut over time,are no garuantee..just my 2 cents worth