How to select gear/sprocket ratios for vehicle?

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SUMMARY

The discussion focuses on selecting gear and sprocket ratios for a vehicle with a mass of 150kg, powered by a 12kW motor with 27Nm torque, and equipped with 110/80 R17 wheels. Key calculations involve determining the wheel radius, which is essential for understanding the force exerted by the motor. The example provided illustrates how to calculate the wheel's diameter and radius, leading to an acceleration of 0.429 m/s². To achieve desired acceleration rates, specific gear ratios are recommended, such as a 5:1 ratio for a 5MPH increase per second and a 10:1 ratio for a 10MPH increase per second.

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The mass of vehicle with driver is 150kg. The specification of motor are 12kw, 27Nm torque, using 110/80 R17 wheels . 1. what is the general consideration to do transmission calculations of bikes 2.How to select gear ratios and sprocket ratio?
 
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"110/80 R17 wheels ." ... This does not help we need to Know the RADIUS of wheel , including tire.
 
oz93666 said:
"110/80 R17 wheels ." ... This does not help we need to Know the RADIUS of wheel , including tire.
110/80 R17 is enough information to calculate the radius/diameter; the 110/80 is a tire specification even though OP said "wheel".
 
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oz93666 said:
"110/80 R17 wheels ." ... This does not help we need to Know the RADIUS of wheel , including tire.
I think the below example will be clear you doubt on calculating radius.
Example: 285/75R16 (285 X 75 / 2540 x 2) + 16 = 32.8 inches tall.
 
I guess 'tall' means dia?? ... In which case we have a radius 0.42 meters

We are told the torque is 27Nm which means if the wheel had a radius of 1 meter , it would push horizontally on the ground with a force of 27 Newtons ...

and this would be the force accelerating the bike and passenger ... but the wheel is smaller and so we get more force ... 27/0.42 = 64.3 Newtons

Since the mass is 150kg , the acceleration is ... F=ma ... 64.3/150 =0.429 m/sec

1MPH = 0.45m/sec

So that's the acceleration with no gears ... an increase of 1MPH every second ... it would take you 20 secs to reach 20MPH !

You need to decide what is an acceptable acceleration 5MPH increase every second would need a 5 to 1 gear... that's 0 to 30MPH in 6 secs

If you want to reach 30MPH in 3 secs , that's an accn, of 10MPH/sec ... a 10 to 1 gear is needed .
 
Last edited:
Since the mass is 150kg , the acceleration is ... F=ma ... 64.3/150 =0.429 m/sec

The 0.429 is acceleration you put it as m/sec how? i can't able to get it.
 
Thathrooban said:
The 0.429 is acceleration you put it as m/sec how?
It's m/s2.
 
A.T. said:
It's m/s2.
yeah that's why I ask him.
 
Thread closed pending moderation.
 

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