How do you choose which brushless motor to run?

[Frankentruck]

When picking a brushless motor, I seem to always go for a 17.5, 13.5, or 10. But I see that 21.5 and 25.5 are both used for some racing classes. Is a larger number rating chosen so you can run really low gear ratios to make good speed instead of high rpms and high gear ratios? Or is it for running on 3S or more? So far on LiPo I've just been running 2S. The 25.5 motors seem like they were used with some VTA racing, which I know nothing about, so I'm not clear why they would be chosen. I understand brushed motor selection getter than brushless motor selection.

[RogueIV]

When picking a brushless motor, I seem to always go for a 17.5, 13.5, or 10. But I see that 21.5 and 25.5 are both used for some racing classes. Is a larger number rating chosen so you can run really low gear ratios to make good speed instead of high rpms and high gear ratios? Or is it for running on 3S or more? So far on LiPo I've just been running 2S. The 25.5 motors seem like they were used with some VTA racing, which I know nothing about, so I'm not clear why they would be chosen. I understand brushed motor selection getter than brushless motor selection.

The higher numbers, 21.5 and 25.5 are just slower motors and often more on par with the old 27turn stock motors. A lot of classes run these to keep the speeds lower with older cars.

[Charlie don't surf]

When picking a brushless motor, I seem to always go for a 17.5, 13.5, or 10. But I see that 21.5 and 25.5 are both used for some racing classes. Is a larger number rating chosen so you can run really low gear ratios to make good speed instead of high rpms and high gear ratios? Or is it for running on 3S or more? So far on LiPo I've just been running 2S. The 25.5 motors seem like they were used with some VTA racing, which I know nothing about, so I'm not clear why they would be chosen. I understand brushed motor selection getter than brushless motor selection.

25.5 and 21.5 are also very often 1S classes, especially on carpet pan car/oval and such classes. 17.5 is a very popular 2WD off road buggy class, also 17.5 Stadium truck occasionally, but typically I see more 13.5 or open Stadium Truck classes. The higher the number the more windings in the stator portion of the motor, and the as a result more resistance and less RPM (all brushless motors are very high torque) the lower the number, the more RPM and torque- 17.5 is like the old 19 turn super stocks IMO and 21.5 is akin to 24 deg stock motors from BITD.

The higher the number, the more expensive it is to be competitive, since little things mean big gains or losses. Very much a "motor of the week" thing i feel.

[RC10th]

Depends what you want...

For spec racing you have to pick what turn motor the class requires.

For general fun something in the 8.0-8.5T is a good choice, and with dynamic timing you don't really need any other motor.

In my opinion 3s+ is only for larger bashers/traxxas