The imagined “consensus” is between enthusiasts who talk to each other online instead of being out riding.
In other words, not necessarily representative of the average buyer of a unicycle. So it comes with 150s as they offer good control and confidence for someone new to riding a 29". I will ignore the fact that 36" unicycles also come with 150s as the default.
Based on what you’ve written so far I would say start with the 125s. Depending on your tastes you might want to go shorter, but if you’re riding on mostly level ground, you are less likely to want to go longer.
I find my 29" with 140s great fun on trails that aren’t very technical or “climbey” but for more difficult stuff I would also use 150s.
My two main unicycles also have 150s. Those are a 26" KH Muni and a geared 36". Both have the dual-hole spirits, and the 125 hole can be really fun on “easy” trails, but hard work on technical or climbs. I doubt I will ever use the 125 holes on the 36" as long as the geared hub is there.
This is probably more true as you and your knees get older (the braking part), but can also be mitigated/eliminated by adding a brake. But you really don’t want to add a brake if you’re only riding on flat stuff.
For me, riding a 29" on pavement with anything longer than 125 is too much work. If you need to make a sudden stop, often a quick turn works better than jamming on the leg-brakes. If I want to get somewhere on a 29" I’ll opt for 102s, but if I’m learning, and just cruising around, those would probably be annoyingly short.
On an ungeared 36", I wouldn’t go any longer than 125 for pavement (mine has a brake). For my local bike path, my “sweet spot” was 114. But when it was new, I was happy to ride with the 150s until I built up some confidence on the beast. They ride very differently from the 45" wheel with the solid tire I’d had for 20 years before my first Coker (and my 45" has 165mm cranks!).
Setonix mentioned dual hole cranks, which make it easier to switch sizes, but if you go for the Trainer, or any other uni with square taper/cotterless cranks, I don’t think unicycle.com has any with dual hole. But at $15 a pair, it’s a much, much cheaper proposition to experiment with different sizes of cotterless! Yes, the cheap ones are steel, but that’s fine, especially if they’re short. Once you find your favorite sizes, you can then upgrade them to the lighter stuff.
Interesting – I never got that. Never felt the urge to boast that “Mine are shorter”… That’s right ladies, I once raced a Marathon on a 36" with 102s (and it was my fastest one ever!)… Nope, I’m still not feeling it.
This is true. I once tried to race George Peck (the grandfather of Mountain Unicycling) on a singletrack trail, him on 175s and me probably one 150s. I wasn’t quite keeping up, and his feet were making BIG circles! So you can definitely learn to spin fast, but it will still take a larger amount of energy. Call me lazy.
True but basically irrelevant because they have all the gearing they need to turn those cranks at the optimum cadence to climb the Alps or speed along the flats. We always have to pedal faster if we want to go faster.