# I need help in figuring out the ratio on motor speed versus gear ratio versus tire size

Discussion in 'Science and Technology' started by Daryl Hunt, Mar 17, 2018.

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### Daryl HuntGold Member

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I am working on a new project. I have been using in hub motors. I want to use a chain driven motor instead. Here is the problem.

The speed of the external motors are 4800 rpm
The available motor drive gears are from 9 to 13 teeth
The available shaft drive gears are from 32 to 89 teeth
The size of the Wheel (OD) is about 20 inch.

I am trying to keep the road speed down to no more than 37 mph. Is this possible in this range? Or am I going to blow well past that no matter what ratio I choose. My math isn't that good anymore.

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### RambunctiousGold Member

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Sprocket Ratio Calculations

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### tyroneweaverGold Member

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Well. If a car has 4800 rpm and has 4:11 differential, what would be the road speed? 60??? Go from there.

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### BULLDOGDiamond Member

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Try this.

a= motor RPM
b= drive gear teeth
c= driven gear teeth
d= wheel diameter

MPH= (a(b/c) * (3.14*(d/2)*(d/2)))/ 60/5280

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### Daryl HuntGold Member

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I came up with a motor sprocket of 8 teeth with an axle socket of 54 on a 20 in wheel at 4800 rpm at 35 mph. Please check my figure.

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