Required gear ratio

[chris.alex]

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]

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]

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]

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

[chris.alex]

I need to come back to the topic, because I wonder how to set the gear ratio of my TT02SR or XM01 Pro to 4.5:1 or 5.0:1 if I ever wanted to join a racing event? Even with the 64t spur gear of the TT02 it's not going under 5.74:1.

Does it mean that the popular TT02 can't participate in most of the racing events? 

[MadAnt]

On 10/25/2024 at 8:09 PM, chris.alex said:

I need to come back to the topic, because I wonder how to set the gear ratio of my TT02SR or XM01 Pro to 4.5:1 or 5.0:1 if I ever wanted to join a racing event? Even with the 64t spur gear of the TT02 it's not going under 5.74:1.

Does it mean that the popular TT02 can't participate in most of the racing events? 

There are some tricks you can do. Some people buy the the high speed gear set and run 48p gears(someone on the forum mentioned it) or do what I did and make the TT01 spur gears work, which is very easy.

[chris.alex]

32 minutes ago, MadAnt said:

There are some tricks you can do. Some people buy the the high speed gear set and run 48p gears(someone on the forum mentioned it) or do what I did and make the TT01 spur gears work, which is very easy.

Thanks for the good advice. I'm going to adjust the 55T spur gear as I've got that lying around anyway. And then maybe I'll sign up for a beginners race next year. 🙂

[MadAnt]

4 hours ago, chris.alex said:

Thanks for the good advice. I'm going to adjust the 55T spur gear as I've got that lying around anyway. And then maybe I'll sign up for a beginners race next year. 🙂

Just keep in mind that it's not a direct bolt in mod, but trimming the gear by the hub is very easy. It's totally worth it if you already have it and have a powerful enough motor to take advantage of the higher speed gearing.

[Losi XXT-CR]

On the other hand, simply don't worry too much about and just give it a go. Chances are you'll have more than enough acceleration and top speed. The biggest reason for messing with gearing in the past was managing run times. On the old NiCd and early NiMh days, getting 5min 30 sec or 6 min runtimes of consistent power was a fine art. Too tall gearing and you may not have made the finish line or could cook your motor.

[87lc2]

This along with 64p gearing will get you anywhere you need to be with a TT02 chassis - https://mttr-rc.com/products/carbon-main-shaft-bearing-holder-front-rear-for-tamiya-tt02

I run anywhere from 3.2:1 - 3.8:1 in my SRX for VTA with a HW G3R motor and it runs fantastic.  Motor has been going strong for a year now and still has lots of punch/power.