Hi there, I have spent the better part of the last 2 months reading up on the forums, and I have found that information regarding this topic is pretty spread out and scattered, making it hard for new users to fully understand it.
What is the difference between 2 setups, with the same voltage and amp output, but one with a high kV motor with high gearing ratio, and one with a Low kV motor and Low gearing ratio? Both are geared for the same top speed
So far what I understand is that the difference is in efficiency, and torque/responsiveness at higher speeds
I hope the veterans and experienced Builders can chime in and contribute their knowledge to this thread and help out some newbies to understand kv vs gearing ratio better.
Good question. Hopefully somebody with a braoder spectrum of trial and error can speak up here, but here’s my experience:
i used to run 270KV 50mm motors at 6S on a 15/36 ratio on 83mm wheels. The motors got hot. The torque wasn’t really present so much, and the top speed was south of 30mph.
I have also run 190KV 63mm motors at 10S on a 15/36 ratio on 83mm wheels. The motors stay cooler, the torque is defeinitely more present, and top speed is around 30mph ish
I now run 190kv 63mm motors at 12S on a 16/32ratio on 90mm wheels. The motors are significant;y cooler at all times, the torque is very very present, and the top speed is well over 30mph, would say 36 or 37 for me. I’ve been clocked at 36 but i feel i’ve been faster on that board.
So what i haven’t done here is run a motor on a higher KV at 12S because i’m already bumping the limit.
I just finished modding an Evolve for which the customer upgraded his motors to 200KV race stars. Same ratio but noticeably faster on the top end then a stock bamboo.
None of this answers your question directly, and i’m sorry for that, but i really feel like the lower KV on a lower ratio is the better option, and higher voltage while doing so is icing on the cake.
10S is likely the best place to experiment with this since at 12S you’re already bumping the KV limit for most VESC based ESCs out there at the moment.
Have you ever burned a vesc with this setup? That should be cutting it close for the erpm limit no? I have a build planned for 12s and 190kv 63 motors too. Holding off until i have more experience and cash
1250 kv 4200w single on 8s 72/9 on 90mm wheel. Inrunner 4 pole 40mmx100mm can. Very small profile light weight. 34mph on a single motor decent accel and will out pull most dual hub or direct drives and uphill. Inrunner motors work above 90% efficiency and the gear drive is the path of least resistance for a ratioed setup with a 100% mechanical connection.
The ERPM limit becomes a false idol when the KV on the motors is wrong anyway. The reaosn i use 190KV motors instead of 200KV motors is because a 200KV motor might actually be a 190KV motor while a 190KV motor is never really quite 190KV.
Hey @longhairedboy , do you happen to know how much torque was lost when switching to the 200KV motors? I have just finished a build using racer stars 140kv dual and while I’m happy with the top speed, I wonder how much torque is lost when you go with the 200kv version of these motors.
didn’t seem too much different on the Evolve. Still had close to the usual start up feel to it so i’m not sure how much of a difference their tuning makes here as well. On a fully DIY board you could adjust the settings in the ESC and probably eliminate a lot of the difference in just settings.
Does anyone have more info on this topic? Is it best to go for low kv and low gearing or high kv and high gearing.
I feel like we didnt get any clear advice here. or am i wrong…
For example on 6S: 200kv low gearing bigger wheels, or 270kv high gearing smaller wheels.
Important thing is how fast do you want to go and how many watts do you need to achieve that goal the rest is balancing your volts, gearing, wheel size and motor kv. Use this tool. http://calc.esk8.it/
Pick a real-world top speed you want to have, like 25mph. Don’t be greedy here, or you won’t have as much torque or braking. Pick a voltage, I recommend 10S (32V - 42V) if you’re using a VESC4. Pick a wheel size, I recommend 97mm - 110mm.
Use an esk8 calculator to find a pulley ratio and motor kv that works for you. You want to maximise the motor kv while staying under 50,000 erpm and matching the loaded top speed you picked.
Try not to use pulleys smaller than 15 teeth for belt longevity.
@MoeStooge spins inrunners a million rpm and maybe gets more efficiency (in the motor) than others. Generally the faster u can zpin the motor the greater efficiency
Think of watts as horsepower. 2000w=2.7hp. If your setup requires 3hp to haul a 170lb load up a 20% grade at 25mph and your setup makes 2.7hp it’s going to heat up. Now gear it for 20mph and your in the zip code and heat is ok. More Watts makes more HP = less Heat. When working with watt limits your gearing is most important for keeping your build from making magic smoke.
I feel like we didnt get any clear advice here. or am i wrong… 
For example on 6S: 200kv low gearing bigger wheels, or 270kv high gearing smaller wheels.