I have an '84 16ft Scamp
. The wheel wells would accommodate 14 inch wheels if the tire cross-section size were to remain the same.
However, a major advantage of going with larger diameter wheels is the availability of larger rim widths that all use of larger cross section tires
In my case, I was planning to replace the axle
and lift the body some to allow the use of six lug 15 inch wheels with 235-75 X 15 tires
, the same as on my tow vehicle.
Unfortunately a couple of years ago I had both 13 inch tires
develop lumps a couple of thousand miles from home and ended up just replacing the tires with the original size.
We use the trailer a lot, so these new tires are already showing quite a bit of wear. In a couple of years I may find time and energy to upgrade to the larger size.