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Toad16v

Final drive ratios and motor turns.

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Afternoon. I've tried searching, but have never found a decent guide, tables etc to help me understand the best final drive ratios to use with different motors.

I'm mostly thinking brushed motors if it makes a difference...

As I understand it, most kits come with a 27t silvercan motor and a 'kit' final drive ratio.

If I fit a 25t torque tuned motor, I think I can get away with a taller final drive ratio as it has the extra torque to cope with it. This is the anomaly.

If I fit a 23t sport tuned motor (or indeed a lower turn motor), then the motor has a higher max rpm, and I should reduce the fdr so that the motor can reach its maximum speed, instead of bogging it down. For instance I fitted a 14t pinion to my terra scorcher instead of the 15t pinion it came with when fitting a 23t motor.

Firstly, can someone confirm that this is right, and can anyone tell me if there is a resource to indicate the ideal fdr for a given motor, depending on its use?

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3 hours ago, Toad16v said:

Afternoon. I've tried searching, but have never found a decent guide, tables etc to help me understand the best final drive ratios to use with different motors.

I'm mostly thinking brushed motors if it makes a difference...

As I understand it, most kits come with a 27t silvercan motor and a 'kit' final drive ratio.

If I fit a 25t torque tuned motor, I think I can get away with a taller final drive ratio as it has the extra torque to cope with it. This is the anomaly.

If I fit a 23t sport tuned motor (or indeed a lower turn motor), then the motor has a higher max rpm, and I should reduce the fdr so that the motor can reach its maximum speed, instead of bogging it down. For instance I fitted a 14t pinion to my terra scorcher instead of the 15t pinion it came with when fitting a 23t motor.

Firstly, can someone confirm that this is right, and can anyone tell me if there is a resource to indicate the ideal fdr for a given motor, depending on its use?

Tamiya gives rough ratios in the manuals of that motors as far as I remember. But honestly in the end, you can do this yourself, depending on the conditions and  surfaces you run on. In the end the limiting factor is motor temperature and ESC temperature. You´re totally right to reduce the pinion size a little bit when using higher rev motors than the kit engine. I propose to give it a run 1 or 2 minutes, and check the motor temperature. If you can´t touch it with your hand after 1 minute, then it will probably get too hot over the whole runtime. Then use a even smaller pinion. Many brushed ESCs nowadays have also a thermal cutoff, when getting too hot or reducing the output power before getting too hot. If you get to this problem, go also shorter, or improve the airflow over the ESC, maybe by an external fan. And don´t forget, that nearly every Tamiya manual recommends to let the motor cool after each battery. If you don´t want to, make sure you don´t overheat the motor, by being even more on the save sade with a higher gear ratio.

That´s about it (at least with brushed motors). Ask many people, and get many different answers, depending on the varying conditions everyone has to deal with. (e.g. high grass vs. open tarmac)

Kind regards,

Matthias

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You'll not find a chart to cover all cars because the final drive [gearbox] ratio doesn't consider the wheel diameter, which could be one of several sizes, so a motor/final drive ratio that works for an m chassis would not work for a touring car or buggy, for example. 

As has already been said, the manuals for individual cars or even the manual for hop-up motor mounts will tell you what is recommended on a per-chassis basis. 

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