I am not sure what the absolute limit might be, but how often do you really need to haul more than a bin full of gravel or logs?. I have done both and the CETMA bike stays rideable. As for hills, I can get it up 500m (1/3 mile) of 15% grade when it is mostly empty (mine is the green bike with the cute toddler) or up a mile or so of 8% with a couple of hundred pounds in the bin. I have a 33 tooth chainring and 34 tooth cog as my lowest gear.