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FDR

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Old 05-27-2019, 09:34 AM
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FDR question

Mine is 96/52 x 1:9 = 3.5 FDR

If I change the spur to 92 with with 49 pinion the FDR is about the same but will it effect the car differently?

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Old 05-27-2019, 09:48 AM
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All things being equal, there will be zero difference between the two regarding speed and acceleration. Doing the math, the second option is a micron lower in ratio which will yield a bit more torque. but hardly noticeable I think.

Now the physical difference is the motor will shift further back a bit with a smaller spur(assuming this is a rear motor car), therefore changing ballast. I typically like more forward wight biased toward the front if I can.
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Old 05-27-2019, 10:29 AM
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The 92 spur and 49 pinion will yield better laptimes on a short track, but the difference will be minimal...I am guessing it will be used with a 25.5t motor which might benefit more from a torque setup than a rpm one....
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Old 05-27-2019, 12:10 PM
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The smaller the gears, the lower the power transfer efficiency. It's not a huge difference at those ratios. You'd more likely notice the change in CG, than anything to do with the gears.
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Old 05-27-2019, 03:04 PM
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Originally Posted by Nerobro View Post
The smaller the gears, the lower the power transfer efficiency. It's not a huge difference at those ratios. You'd more likely notice the change in CG, than anything to do with the gears.
Excellent posting. This is correct. Larger gears will have a slightly higher contact ratio (average number of teeth in mesh) which will yield a very small increase in gear mechanical efficiency. But moving the motor forward probably has a bigger effect in handling.
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Old 05-27-2019, 03:18 PM
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Of course take everything I say with a grain of salt because Iím really old. When I saw the title of this thread, I thought it was about our 32nd President.
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Old 05-27-2019, 10:15 PM
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Originally Posted by glennhl View Post
Of course take everything I say with a grain of salt because Iím really old. When I saw the title of this thread, I thought it was about our 32nd President.
This is the best answer.
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