What gear ratio to use with brushless?

[joel45acp]

I have an RC10T3 with stealth tranny, Reedy DS Spec motor, Novak 610RV ESC, 3k NiMh packs and 14/54 gearing. My two buggies have the six gear tranny. One will have a Novak 610RV using a Speed Gem 2 (blue can) and has 17/87 gearing. The other has a Trinity TI 9x2 motor, 21/87 gearing and hopefully using a Novak Rooster. What would be the best gear for racing and bashing on these RCs if I decide to use Lipos (Turnigy 5000mAh 2S 40C) or similar packs? I know I'm asking a lot, but any info is greatly appreciated gents. I saw the Lipos advertised cheap at Hobby King with free shipping. Currently, the RC10T3 is the fastest by far with current gearing, but any info would be great. Thanks in advance.

[Erich Reichert]

Hey Joel. First things first... I'm not 100% sure but I would recommend something with a lower motor limit than the Rooster if your going to run a 9 turn motor. I looked really quick and i believe it's specs cut off at 15 turns. 9x2's are going to be really tough on the esc and it will almost assuredly blow on you. I would recommend putting some money into a better esc before you run modified motors in general.

As for your question, with brushless you want to gear up (bigger pinion/smaller spur). I wouldn't give advice on actual gear ratios as I don't know the length or style of the track you want to race on but here's a good rule of thumb. You want the motor to top out about 1/2 - 2/3 of the way down the longest straightaway. Once you have a gear your happy with for that you can tailor it up or down to help with the corners. If it has tighter corners and the car feels like it bogs in the corner, go down a tooth or two. The best thing to do would be to find someone there and ask what gear ratio they run. NOW KEEP IN MIND... your 6 gear's internal ratio is MUCH lower than theirs will be if their running a B4 or something more modern so you will want to calculate the final ratio using this formula (assuming your tires are the same or about the same diameter as theirs).

Spur / Pinion= X
X * transmission ratio = final ratio

For Example: 87 spur, 21 tooth pinion, 1.85 is the 6 gears ratio

87/21= 4.14
4.14*1.85= 7.66 (this is your final ratio)

So now what you can do is ask someone "hey what gear do you run" and "what is your transmissions ratio" and you can figure out what their final ratio is. Then you can take that final ratio, divid it by 1.85 (your tranny ratio) and this will give you your gearing ratio. Take THAT and divide it into the spur like this...

Say their final ratio is 8.4 and they have a B4 (tranny ratio 2.6)

8.4 / 1.85 = 4.54 (this is the ratio you'll want for your spur/pinion
If you have a 93 tooth pinion its: 93 / 4.54 = 20.4 (this is your pinion... round to 20 teeth)

[joel45acp]

Thank you sir for the wealth of info. That is just awesome.