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Gearing - more or less teeth over all ?

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Gearing - more or less teeth over all ?

Old 11-12-2017, 12:53 PM
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Questions?? Gearing - more or less teeth over all ?

Hi all,
I run a 1/10 touring car with 64pitch gearing. My internal ratio is 1.85.

If for example I ran:
a 100t spur and 44t pinion I would have a final drive ratio of 4.205
or
a 116t spur and 51t pinion I would have a final drive ratio of 4.208

(Putting aside the very minute difference in FDR) Obviously running option 2 above I have more teeth in my gearing over all.

Theoretically the strain on the motor would be the same.. ? I don't know

My questions are,

- would there be any difference to the drive of the car? (acceleration, speed, etc)

- and are there any advantages or disadvantages of each situation?

Many thanks for any responses!
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Old 11-12-2017, 05:42 PM
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Not sure how you'd ever fix 116T spur with a 51T pinion but in doing so you'd move the motor more forward. It alters the weight bias in the car. I'm not a good enough driver to feel a difference so I don't worry about it too much but I know that for the Schuey Mi6Evo, they have an even larger than 116T spur to get the motor to shift further forward
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Old 11-12-2017, 08:43 PM
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Thanks for the reply. My examples are theoretical and in the second case a rather extreme example, but they are just example to aid my question.

And you are correct, there is physically no way I could fit a 116t spur with a 51t pinion in my car.

Thanks, I hadn't thought about motor position tuning, there is only the physical possibility to shift my motor forward or back by about 7mm so tuning is that respect (wight bias) is limited in my case.

There are of course lots of spur-pinion combinations that would indeed be possible in my car and result in practically the same FDR.
For example if i wanted an FDR of 4.51 I could go with a 100t spur and 41t pinion, or, 105t spur and 43t pinion.

Any thoughts? Thanks again for any help!
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Old 11-12-2017, 08:48 PM
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As WagwanBumba said, the only thing it'll change is the position of the motor. There will be no difference in acceleration or speed if the FDR is the same. The motor is pretty heavy, so even a 7mm movement will affect weight distribution.
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Old 11-12-2017, 08:57 PM
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Run the biggest gears you can fit, while it may not be faster it is more efficient
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Old 11-13-2017, 01:33 PM
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The larger gears overall are slightly different, but most likely negligible. The larger gears have more rotational inertia, which will very slightly reduce acceleration. And the larger gears will have a slightly higher gear contact ratio. The mesh will be just slightly less efficient. Again, it's negligible. But the larger spur gear will stick down further and might get damaged more easily if you hit a rock that happens to stick into the chassis clearance hole for the spur gear.

Last edited by glennhl; 11-13-2017 at 01:46 PM.
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Old 11-14-2017, 10:59 AM
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If FDR remains the same after swapping pinion/spur, I would anticipate the motor position not changing.

I was wrong about this.
Code:
FDR is related to total tooth count, and whether you're running 50/100, 100/50, or 75/75, you still have the same number of teeth and the motor position should remain the same
Additionally, there is no performance difference between one pinion/spur combo and another if the FDR remains the same.

Last edited by JoshuaRC10; 11-14-2017 at 01:08 PM.
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Old 11-14-2017, 12:24 PM
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Originally Posted by JoshuaRC10
If FDR remains the same after swapping pinion/spur, I would anticipate the motor position not changing.

FDR is related to total tooth count, and whether you're running 50/100, 100/50, or 75/75, you still have the same number of teeth and the motor position should remain the same. Additionally, there is no performance difference between one pinion/spur combo and another if the FDR remains the same.
What? No. FDR (final drive ratio) is the ratio, not total number of teeth. Large spur with small pinion gives a very different ratio to small spur with large pinion, even if the total tooth count is the same.
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Old 11-14-2017, 12:26 PM
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Originally Posted by gigaplex
What? No. FDR (final drive ratio) is the ratio, not total number of teeth. Large spur with small pinion gives a very different ratio to small spur with large pinion, even if the total tooth count is the same.
Ahh. You’re right. I was getting confused.
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Old 11-14-2017, 12:31 PM
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Same total number of teeth = same motor position - yes.
Same total number of teeth = same FDR - no.

Same FDR = different motor positions.
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Old 11-14-2017, 01:02 PM
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Originally Posted by JoshuaRC10
If FDR remains the same after swapping pinion/spur, I would anticipate the motor position not changing.

FDR is related to total tooth count, and whether you're running 50/100, 100/50, or 75/75, you still have the same number of teeth and the motor position should remain the same. Additionally, there is no performance difference between one pinion/spur combo and another if the FDR remains the same.
I'm pretty you might have that confused. 50/100 is .5:1____100/50 is 2:1____75/75 is 1:1
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