Optima Mid spur gear ratio - give me a starting point

[Coelacanth]

My current project is an Optima Mid that's going to be setup as a mid-motor RWD. It has the ball diff gear innards of a Turbo Optima Mid SE, I'll be upgrading the balls to ceramic and will polish the diff plates to smooth (wet-sanding with 1500-grit).

The stock spur gear & slipper on this car has been upgraded to a 48-pitch fine-tooth Robinson Racing gear. I received in this parts lot a series of RR gears, from 75T to 93T I believe, and one pinion gear to match that's a 14T. I believe the previous owner had it setup with the JG Racing truck conversion.

I also received a bunch of stickers showing all the various pinion/spur gear ratios but I'm not sure which spur gear I should start with; a smaller or bigger one? I'm installing a 12T brushless motor & ESC combo from Toro.

http://www.ebay.ca/itm/SKYRC-toro-leopard-12T-2p-Brushless-Motor-3300kv-60A-V2-ESC-RC-car-truck-buggy-/290825206167?pt=US_Character_Radio_Control_Toys&hash=item43b6887997

That all being said, I'm intending to run it as a RWD-only and would like some suggestions for a starting point for a final gear ratio...what combo of pinion & spur should I start with?

[Coelacanth]

Thanks to all the crickets for answering...how about some Optima Mid enthusiasts?

EDIT: Looks like I have a starting point, anyway...the very last post in this topic on Oople suggests an 18T pinion & 81T spur gear. Thanks crickets!

http://www.oople.com/forums/showthread.php?t=4888

[klavy69]

I would start with an 18T pinion & 81T spur gear...

Todd

p.s. it actually is what my optima mid is at but I have no real idea

[jwscab]

what is the internal ratio? The 18/81 is a good start if the internal ratio is around 2:1 or so. Really, with a brushed motor you are gearing for run time and motor temps, so you will have to adjust from there.

[scr8p]

according to a twister motor sheet, the optima mid is a 2.64:1.

[jwscab]

whoops...the 12t thing confused me, I thought you were running brushed. 12t isn't a 'common' brushless wind.


so you are concerned with motor temps. with that internal ratio, the 81/18 is probably fine, but you may find you will be going up a bit on the pinion. Better to work your way up to motor temps than to smoke it being overgeared.

[Coelacanth]

what is the internal ratio? The 18/81 is a good start if the internal ratio is around 2:1 or so. Really, with a brushed motor you are gearing for run time and motor temps, so you will have to adjust from there.

What scr8p said. He must have some Kyoshos stashed somewhere...

[Coelacanth]

Thanks gents, I'll see what spur gears I have, I have a good selection to choose from...48p pinion gears, not so much.

[klavy69]

What scr8p said. He must have some Kyoshos stashed somewhere...

you know its true

Todd