Required gear ratio

[chris.alex 1050]

Recently at a club's race track, I heard that in many competitions, a gear ratio between 4.5:1 and 6.5:1 is usually used. I find that remarkable. Doesn't that put a lot of strain on the motor, even a 21.5t one? Why is it done that way? 

[SlideWRX 880]

At a competitive level a motor can be a consumable, like tires. It puts strain on the motor, but only for 5 minutes.  The goal is to run it at the highest possible gearing & timing advance without burning out during the race/race weekend/race season, depending on budget.

[Jonathon Gillham 4672]

I run about 2.8 in my F1 with a 21.5T and the 21.5T touring car at about 3.7 from memory. The motors handle it fine, until they don't.  If you get the gearing right you have a motor that will last a couple of years without giving up top speed. Brushless motors have so much torque, they have to be geared that way. Its also why the times between 21.5T and mod are often very close (unless the track has a lot of long straights) as the cars aren't that different in speed given the small tracks.

[chris.alex 1050]

Thank you guys for your explanations. The increased torque of brushless motors obviously makes things different.