We used to set up adult trikes for use at various swap meets and car shows after they banned golf carts.
They were often held in rough fields, parks with rolling hills, and we often used them to carry crazy amounts of weight, such as car engine blocks, cylinder heads, and transmissions. A few were set up with mini trailers too.
All but one had 24" wheels, one got converted to 26" wheels and was built using the frame and fork from a Schwinn Typhoon attached to the rear axle of a Town and Country trike with custom 26" rims laced to modified trike hubs. (I made 36H flanges and hub centers to fit the stock Schwinn axles with set screws to secure the hub on the axle in place of the stamped key way.
Needless to say they needed a lot of help in the gearing area. We only used three speed models. Most had Shimano 333 rear hubs.
The normal gearing on a 24" trike was a 36t front sprocket and a 24t rear cog. This worked well on the 24" models but the larger wheels needed ore help and I hunted down a 26t rear cog for that one. It worked but third gear was almost never used. It needed a lower ratio.
The 36x24 gave a 1.50 ratio, the 36x26 was 1.38. One of the guys trash picked a single speed department store trike and its original 44x20t configuration was horrible. The bike used an odd ball freewheel in the middle of the right rear axle, basically a welded in place BMX single speed freewheel. There was no easy way to change the rear cog.
I used a 36t front sprocket and since it was a fixed speed model I ended up taking the rear freewheel apart on the axle, then I TIG welded a single 30t rear cog over top of the original 20t cog to get a 1.20 ratio. That worked but even then could be a bit hard to pedal up even minor hills over distance.
(That rear freewheel eventually failed, breaking a few of the internal pawls and locking it up as a fixed gear, this all happened on a long downhill run while attached to a trailer, the guy riding it laid into the only brake, the front caliper which grabbed for a bit then the cable pulled out of the clamp and he had no choice but to ride it out. The trailer was carrying four 8 gallon jugs of racing fuel. We were watching from behind laughing so hard we had to stop and watch what we thought was going to be a hilarious wreck. All we saw was the extra long BMX cranks spinning like propellers and him with his legs lifted way clear of the spinning cranks. He somehow managed to ride it out, he even managed to navigate a slight curve heading back down toward the pits. We were really expecting him to end up in a drainage ditch off to the left when he hit the curve. He finally figured out a way to drag one foot enough to get it stopped once on flat ground. One of the other guys hopped on it and showed him how he should have just used his foot behind the front tire to stop the trike and managed to wack himself in the calf with the pedals while do so.)
35 years later and that trike is still hanging from the ceiling in that guys shop. I took that freewheel apart and I don't think it failed due to the welding of the sprocket, I think it was just too light duty for the task at hand and the super low gear ratio and torque it was seeing pulling a lot of weight. None of us were lightweights then either.
On my Nishiki 26" Pacific cruiser I've got a 46t x 22t combo (2.09 ratio), which works fine for the fairly flat roads around here but if I were still living where there were hills, I'd likely want a much lower ratio. Speed wise it goes fast enough for what it is and having only a coaster brake, its just fine.
(Its got no provision for a front caliper). If i were to need to ride where there are hills, I'd likely take one of my bikes with a three speed SA hub and a 42x20 ratio. which when combined with the low and intermediate gears in the hub make for a pretty easy climb on most hilly roads. (About a 2.10 ratio in high gear).
I tend to stick to flat local roads and on occasion the boardwalk or park trails with my cruiser. If i want a workout I'd go to the gym.