Ok, this has been done before, but lets do it again...
find a motor on the sim with a kv of x.
find the same motor but with a kv of 2x.
Feed motor x with voltage 2v and current limit a
feed motor 2x with voltage v and current limit 2a. (current limits should be for phase windings, but iirc the ebikes.ca sim does an ok job of this anyway using battery currents)
you'll see identical (or close enough too) torque and power curves for a given wheel size, as well as time to overheat, and top speed. because each motor is identical in terms of how much torque it can produce at a given rpm. Just one motor needs 2a and 1v and the other 1a and 2v. VA=P/rpm=T after all. And A^2R=P(heat), but R(2x)=0.25R(x), so P(heat 2x)=P(heat x) for any given Pout at a given rpm (ie any given torque output).
Note - if the torque/power curves aren't very close then this would highlight a limitation of the sim, or potentially your comparing 2 motors where the copper fill of a particular winding is worse than the other.
Now, lets run motor x in a wheel size 2d, and motor 2x in a wheel size of d, but with their voltages equalized.
Motor 2x can still handle 2x the current of motor x, but its also got double the reduction. because its also got 2x the voltage, it can also still reach the same speed, but with its extra reduction its now producing 2x the torque at the wheels, for a given Pheat produced. Remember that we haven't changed the current levels, so each motor will still overheat in approximately the same amount of time. It will naturally require more power from the batteries to produce that extra torque - but thats the price of more acceleration. Another way of looking at it is that it can produce the same torque for half the heat produced, so it can do the same acceleration for longer... and have a much higher top speed (and thus mid-high range acceleration) to boot.
Put simply, other than practicalities around the amount of reduction you can get in a particular space/efficiency of each stage (or wheel size) and rpm limits of a given controller+/motor, your generally going to be better off with a higher kv and more reduction.
We could 'try' the same with motor x, by doubling the pack capacity and by extension the currents driving the motor, but increasing current may mean more torque, but it will also mean more heat (4x the heat for the same torque as motor 2x). The other way is to double the voltage again to 4v and halving the wheel dia to d as with motor 2x, but this has the drawback of (generally in ebike terms) needing larger voltages that make controller choice limited, and battery management more difficult, with the only advantage being smaller phase/battery wires, and (very slightly) lower end turn losses. a 80v pack is much safer to deal with than a 160v pack too.
Its a bit differnt for RC motors, as generally they're designed for voltages <50v, to attain their max speed before losses become too high (something most hubs never get close too). So a lower KV RC motor (such as the REVOLT motors) is not such a bad idea, given that running '2 times' the voltage (to pick a value) is still pretty easy, without needing very high voltages.
For the OP
Probably best to go for the higher kv motor. Id recommend sticking below 1:3 or so per stage, any more becomes very inefficient, ie a single 1:9 reduction will usually be less efficient than 2 1:3 reductions. The only time you'd want a lower kv is if after whatever reductions you plan your motor still is capable of about 20% more speed than you want. the lower KV motor will be easier on your controller (though minor benefit if your not right at the ragged edge of its capability). Neither motor will be 'better' than the other in performance, assuming you can find a controller/battery combo to provide it with the appropriate voltage and current (ie more current but less voltage for the higher kv motor, and inversely for the lower kv).
eTrike said:
Thanks John.
I shared before that I used identical power levels to make that spreadsheet that shows the results from the sim.
The sim does report acceleration in the bottom right corner but I've found few people pay attention to that or their power curve when deciding which motor to use. Many end up with a lot of potential performance (acceleration) left untouched because they choose a fast wind in a large wheel.
Thus the results from the sim show clearly that gear reduction (smaller tire) is warranted for fast winds especially at high speeds. I know I'm not describing anything new to you, but for future readers it helps to illustrate the point.
So, assuming you have a working ebike and only want to change your motor with a different Kv motor and wheel, you can compare those apples-to-apples using the same power settings to confirm the results I've gathered from the sim.
I also shared that I tried varied inputs to suit the motor with high Kv motor double current and gave the low Kv double voltage (which would require swapping battery and controller so this isn't a very likely scenario) in order to gauge the results. You didn't reply when I shared this and asked for clarification for inputs to try in the sim.
If you prefer apples-to-oranges I will concur with what I have not disputed-- the higher Kv motor can take more power. But for apples to apples, I think the sim results ought to be favored over subjective experience (though your experience ought to be verifiable and reflected in the sim, which you've yet to be able to provide despite multiple polite requests). It is certainly good for more than just efficiency.
My roller coaster experience and results are verifiable in the sim. I've used a high Kv 9C in 26", then swapped to a low Kv 9C in 26", then swapped to a high Kv MXUS in a tiny 16" bike rim. With the exact same power system (battery and controller) used between all three. This is why I made the spreadsheet, to compare real-life results. My experience directly reflects what the sim shows.