Brushed ESCs and 550 vs 540 motor limits

[Bottom Feeder]

I've seen a few brushed ESCs that advertise they will run 550s but the motor turn limit is usually lower than what 540s it'll run. The Traxxas XL-5 is a good example, 12T 550 vs 15T 540. Why is that? Wouldn't a torquey 550 pull more amps and strain the ESC more than a same-turn 540 would?

[Frankentruck]

It could be that Traxxas knows all about the tuning and characteristics of their fixed timing 12T 550 motor, but nothing about whatever random 540 motor might get installed. That could lead a manufacturer to declare a conservative limit.

[juicedcoupe]

First, turn limits are more like recommendations. Amp draw and cooling will determine the true limits.

Second, the armature on a 550 is longer. So each turn requires more wire than a 540. And while this creates a motor with more torque, they are also rpm limited.

Finally, application. Vehicle weight, gearing, battery capacity, terrain, and even your driving style will factor in.