And what crank length are you currently using? Did you go to 75mm yet? Because on a 28" that is a gain ratio of 4.74, which is higher than my penny farthing (54" with 150mm cranks = 4.57) and hence should be exceptionally hard work with hills, I would imagine. Or does the light weight of the uni and tyre make it doable (the penny weighs 13.5kg)? I have also been running a plus size tyred 24" with 89mm cranks and that is hard enough, but I suppose that uni is relatively heavy in the grand scheme of things. Nonetheless 28" with 75mm seems like it would be too much for all but flat road.