Assuming everything else is the same (car, weight, battery, gearing, ect) what is the advantage of a lower kv motor over a higher kv motor? Is it just that a lower kv motor has longer run times?or is there more to it? I know that the kv rating is directly related to rpm. so i know how that works but I am wondering if the torque is the same assuming all other factors are equal.

I have a rc18t with a 4120kv tacon motor. I have ordered a new tacon motor that is 7800kv. will the new 7800kv motor have the same amount of torque as the 4120kv motor? or will the 4120kv have more torque than the 7800kv? from what I understand the 4120kv will give me longer run times and of course the 7800kv will give me higher rpm. is the runtime the only trade off? or am I going to be loosing torque as well by going to a higher kv motor? will the truck perform the same at slower speeds with the 7800kv motor as it did when running the 4120kv motor?

Thanks

In general, lower kv means more torque less speed, but if you didn't change the gearing higher (higher gearing=less speed, more acceleration) to compensate for the extra current draw, you will melt stuff pretty fast. Higher kv means more speed, shorter runtimes and more heat. In your case, you will lose a little torque (which will be gained back as you gear up to compensate). In actual fact, the longer the can (and therefore longer magnets, stator and windings) is what really defines the torque.

In a theoretically perfect world, if you didn't have the heat issue and your ESC, battery and motor were capable of delivering and accepting the amperage that the motor wanted to pull, and both motors were the same can and stator length, there would be no loss of torque, but in the real world, the slight loss is noticeable. My 7500 M18T pro doesn't pull wheelies, even on 3s. If I went to 5000kv or less and geared down to keep some of the speed, I would likely have trouble keeping the front wheels down.

Hope that kind of explains it for you.