I recently sold my off-road motorcycle and replaced it a few days ago with a Kawasaki Versys 650
Fortunately, I already have what I believe may be the most suitable APRS set-up for the limited space available - a Byonics Micro-Trak RTG.
But then I started looking at recommended RF density safety levels and am re-thinking the whole idea.
The FCC has published Maximum Permissible Exposure (MPE) limits and expresses those values in mW/cm². To convert a known power output in watts to a density level requires antenna gain and distance to "area of interest" to also be known. This online calculator simplifies the calculations. A downloadable Excel spreadsheet can be used as well.
The results are such that it doesn't seem possible to operate a 10-watt APRS transmitter on a motorcycle without exceeding the recommended limits. I wonder how this compares to the RF density level of a cell phone held directly to the head...