There are two different types of rc motors. Brushed and Brushless. Each motor type has its own kind of ESC (Electronic Speed Controller). Without an esc, your motor would just do nothing or go full throttle when you wanted to drive. Brushed motors are cheap but very ineffecient and lact power. The ESC's are also cheaper. Brushless motors are efficient, powerful, fast, and last much longer. Brushless motors and ESC's do not really have an expiration date, while brushed usually last about 6 months to a year. The main visual difference between the two is the brushless is sealed completely and has three wires, while the brushed has ventilation holes and two wires.
Brushless Upgrades
If you are looking to buy a brushless motor you have a few choices. First, choose your brand. Hobbytron is the cheapest. There is also Mamba Max and Sidewinder but these are a bit more expensive. If you are upgrading from a brushed car, you should buy a combo, which includes the brushless motor, a brushless ESC, and usually a programming card so you can change your preferences (ie. brake force, inital punch, low voltage cutoff, etc.).
MOTOR RATING
brushless motors are labeled with two things, a large number followed by "kv" and a smaller number followed by "t". Basically, you need to check the ESC for that motor and read up a little. It will tell u what numbers followed by "t" will be good for your use. So if you want it offroad you will want more "t", but you will get less "kv". On-road is the opposite.
KV stands for the amount of rotations per minute per volt. So if this basically means the bigger the number, the faster your car will go. Just make sure if you want your car to drive good offroad you get a motor with the correct "t".
For example, my brushless motor was a 6000kv 5.5t brushless combo. I checked the ESC and it said you need greater than or equal to 5.5t for on road and greater than or equal to 8.5t for offroad. I got an on-road motor so i could go fast (about 45mph). If you wanted to go offroad you could buy the 4000kv 8.5t motor, which goes about 35mph but has more power. If you do not understand something here pm me. I will be glad to help.
T Rating
Using an R/C car as an example; lower T values, like 4.5T, will results in a much faster car, as the torque is lower but the Kv will be higher. Higher T values, like 27T, will be a higher torque, lower Kv motor. Crawlers would usually use a high T-rating motors, while touring cars and drift cars would go with low T-rating motors.
