The post above mine is mostly correct. The 1/10th motors are general 540 sized, with some being 550 sized (the motor can is a few millimeters longer) for heavier trucks etc.
Emaxx and Revo, you'd want to use something like an 1/8th scale setup, or a motor at least in the 36x60 or 36x70 mm size range, that means they have a longer rotor and thus can make more torque.
Why use a lower Kv motor in larger scale models? Because they are inherently more torque, inversely to their Kv rating. If given 2 motors of the same size/shape and even brand, a larger and or longer motor, will generally be able to handle MORE amp draw (current) and thus produce more torque (more amps a motor draws, more torque it CAN make).
If a motor is heating up, it means it is overloaded and either you use a smaller pinion, and or larger spur, or you replace it with a lower Kv motor, or maybe if you're way off base, a larger motor.
So yes, 90% of the time if your motor is overheating, you want to try a smaller pinion (2-3 teeth lower and test again every 5-6 minutes). SOMETIMES if you gear the motor way too low (too small of a pinion etc) it can heat up also, due to excessive RPMs and other technical reasons, but this is not as common.
If you look at the specs of most brushless motors of varying quality and sizes, you'll notice the larger ones can usually handle more amps than smaller ones.
Hope this helps.