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Discussion Starter #1
I would like to know what is a good starting point for gearing a novak 17.5 motor and gtb 6 cell esc for a traxxas slash, as for wheels and tires i have proline split six beadlocks with proline bow ties. i am running a smc 5200 24c racing lipo what is a correct set up for the chassie. any info would be helpful thank you.
 

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When trying to figure out what gearing to use, you need to take two main things into consideration - the type of car (2wd buggy, 4wd buggy, stadium truck, CORR Truck, etc), and the number of turns on the motor (7.5, 10.5, 13.5, etc). Those two things will determine what your FDR (final drive ratio) should be.

In your case, for a CORR truck and a 17.5 motor, your FDR should be about 7:1. That number is derived from testing done by the motor manufacturers. They test to see how high of a FDR they can get before the motor starts to overheat. The FDR may be slightly different for different motor manufactures, but not by much.

Now that we know what FDR ratio you should have, let's figure out how to get it. The first thing we need to do is find out what your car's internal transmission ratio is. From doing my research, it appears to be 2.72. The next thing we need to know is what size sput gear you have in your car. Again, from my research is seems to be either a 83, 86, or 90 tooth.

We now have all the information needed to plug into our formula to determine what pinion gear you should use:

PinionGear = SpurGear / (FDR / TransmissionRatio)
PinionGear = 83 / (7 / 2.72)
PinionGear = 32.25143
PinionGEar = 32

or

PinionGear = SpurGear / (FDR / TransmissionRatio)
PinionGear = 86 / (7 / 2.72)
PinionGear = 33.41714
PinionGear = 33 or 34

or

PinionGear = SpurGear / (FDR / TransmissionRatio)
PinionGear = 90 / (7 / 2.72)
PinionGear = 34.94143
PinionGear = 35

So, assuming that the internal transmission ratio of your Slash is 2.72, and you are using a 17.5 turn brushless motor, you should use a 32 tooth pinion for a 83 tooth spur, or a 33/34 tooth pinion for a 86 tooth spur gear. Don't bother with the 35/90 pinion/spur gear setup).

That will get you started and pretty close to where you want to be. From there you can go up or down 1-2 teeth on the pinion and see what happens with the feel of the car and the motor temperature (which should be below 160 F after a 5-6 minute run).

If all this is just too much damn information, you can use my brushless motor gearing guide to quickly determine what gearing you should use.
 

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Discussion Starter #3
Thank you craig v for your reply and yes the info you provided is very helpful.as i sat and read what you have said i begin to wonder if a 34 tooth pinion gear is the highest gear from testing, would a 32 tooth gear give my slash more torque and just about as much high end speed or would a 33 34 pinion gear work all the way around, and still keep the temps under 160f? thanks
 

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The only combo (pinion/spur) that will work is the 32/83. There is only enough room for that combo the others are correct but will not fit without modification to the motor plate and gard.
 

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MoMc,I run a 17.5 in my slash,and use the stock 86 spur with 28-29 for a heat race,4 mins. and drop down to 24-25 for running around my track at home.Keep your eyes on the temp,pending your runtime.HTH
 

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I have raced mine for ten weeks on an oval with a traxxas 76 tooth spur,37-39 tooth pinion.I won the championship with it. I am running the novak combo too. temps at the end of the run is 150. it is much faster than running the 86 or the 83 tooth spurs.
 
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