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I copied and rephrased this out of another thread. I see this mis-stated so much on these boards that I thought it would be good to post it here and clear this up.

This is actually a half-truth. A lower KV motor will have more starting torque, ie. torque from a dead stop. If, for instance, you are pushing it into a wall, or towing something, the starting force will be greater per unit current.

But this is just starting torque. Once the motor starts spinning, at the lowest PWM duty cycle of the ESC, your torque is going to be (theoretically) equal no matter what the KV of the motor is. Anyone that thinks different is forgetting how an ESC works and what KV means.

Remember how the ESC works, using PWM duty cycle to create a limited voltage on the motor. For instance, a 20% duty cycle means that the voltage is 1/5th but the current will be 5x. 10% duty cycle means 1/10th the voltage and 10x the current. Etc. By 10%, I mean if the ESC provides 100A, 1V at the motor (100W), a 10V battery would see a drain of 10A from the ESC (100W) -- if the ESC were 100% efficient.

As for KV, say your battery provides 10V for the sake of simplicity. Likewise the battery can provide a fixed amount of current and no more. If the motor were spinning at 10000rpm, a 5000KV motor would require 2V (0.2 duty cycle) and the 10000KV motor would require 1V (0.1 duty cycle). Of course the 5000KV motor has twice the turns of wire so it generates 2x the torque per amp as the 10000KV motor. In theory, everything is equal in the end. Once you bring PWM into the picture, you are dealing with power and not current, you are dealing with power.

The only way a lower KV motor would have greater torque is if an ESC was just a simple linear voltage drop-down circuit whose efficiency was like a linear regulator (ie. 10V -> 5V = 50% efficiency, 10V -> 2.5V = 25% efficiency).

Now here's the 'gotcha'. Most of the time we are dealing with a 'family' of motors like Castle's CM36 series. The motor is basically the same only the turns of wire is different. That's when the above holds true.

But, ultimately the 'max torque' of a motor is determined by its design, the coil core meteriel, the rotor size, the can size, etc. As the RPMs increase, this torque is flat to a point but then starts to drop off. By the time it reaches max RPM, the torque is very close to zero.

If you take a motor like the VXL motor (3500 KV), that is a family of it's own and it's only desgined to work with 3s LiPo. This means a lower RPM and hence they can design it for a greater max torque -- for instance a fatter rotor. A rotor that might break apart at 60,000rpm, but it doesn't need to go 60,000rpm, so that's okay. If you are going from one family of motor to another, the max torque isn't going to be the same, it's going to depend on the overall quality of the design and the parameters that design was made to meet.