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Old 11-14-2008, 02:54 AM   #1
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Default Quick gearing question

Hi guys,

Just a question about gearing that I hope you guys can help me with since I am still grasping the electric scene. First of all I have a Kyosho TF-5 RTR and changed the stock motor that came with it to a Reedy 19T Challenger motor. Now the Reedy motor has an optimal ratio for rubber touring of a 6.4:1 and the Kyosho transmission ratio is 4.7:1. The stock gearing I have is 36/68 so please explain to me if I'm doing this right. Under those gears i should have a 8.88 so does that mean I have to change the pinion to roughly 49 to 50 to get gearing suitable to the Reedy motor? I hope I'm making sense for I'm confusing myself a tad bit as I read what I'm writing!

And if I'm on the right track what is the biggest difference if I go a few more teeth up or down? Is there a good overall setting I can do for both bashing around/weekend fun racing?

Thanks guys and also one more thing: Does the carbon fiber upgrades make a significant difference to the car and is it worth doing?

Thanks heaps.
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Old 11-14-2008, 02:56 AM   #2
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oh and does running the new motor with the current stock gearing going to damage it in any way? I ran it today and the motor wasn't too hot so I think that is a good sign, right?
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Old 11-14-2008, 04:29 AM   #3
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According to gearchart.com, the transmission ratio of a Kyosho TF5 is 1.83:1, so with 36 pinion and 68 spur you're at 3.46:1, NOT 8.88...

If I were you, I'd visit http://www.gearchart.com then click on the gearchart creator, and select the Kyosho TF5 option from the list of cars, then start plugging in numbers to find the pinion/spur combos that will get you the ratio you need.

You'll have a hard time getting to 6.4:1 with the 68 spur, you'll probably need to go bigger on the spur because even with a 21 pinion, you only get to 5.05:1 using a 68 spur.
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Old 11-14-2008, 04:33 AM   #4
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gearchart appears to have the stallion which is a belt-drive car having a different internal ratio. You could use an assoc. TC3 for a similar 2.5 internal ratio to build a gearchart.

For RTR shaft-drive. 4.7 is their "gear ratio" which is what you are thinking is their transmission ratio. The Kyosho has a "transmision" ratio of 2.5 and RTR FDR of 4.7. Is the stock motor the G20? I think that's a 20-turn motor, but you'll have better performance with the 19T. Going 20T to 19T is "pretty minimal" in terms of motors, so dropping down one tooth on the pinion may be all you need. It's ok to have a smaller FDR - you get higher top-speed at the expense of quick acceleration. You may want to try a 34T and 32T pinion just to step down a bit. If you went all the way down to the "optimal" ratio, you'd be about 27T. Much slower top-end speed but more zippy around the bashing area.

FDR is Final Drive Ratio

Here's what they did:

(68/36) * 2.5 = FDR 4.72

So, compute a smaller pinion into that for the optimal FDR for any replacement motor.

(68/28) * 2.5 = FDR 6.0
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