How to select gear/sprocket ratios for vehicle?

In summary, the conversation focuses on the specifications of a bike, including its mass, motor, and wheel size. The main considerations for transmission calculations are to determine the gear ratios and sprocket ratio. The conversation also discusses how to calculate the wheel radius and the force of acceleration. The desired acceleration and gear ratio must be determined to reach a specific speed in a certain amount of time. The conversation ends with a clarification on the units of acceleration.
  • #1
Thathrooban
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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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  • #2
"110/80 R17 wheels ." ... This does not help we need to Know the RADIUS of wheel , including tire.
 
  • #3
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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  • #4
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.
 
  • #5
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 .
 
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  • #6
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.
 
  • #7
Thathrooban said:
The 0.429 is acceleration you put it as m/sec how?
It's m/s2.
 
  • #8
A.T. said:
It's m/s2.
yeah that's why I ask him.
 
  • #9
Thread closed pending moderation.
 

1. What is the purpose of selecting gear/sprocket ratios for a vehicle?

The gear/sprocket ratio is used to determine the speed and torque of a vehicle. By selecting the appropriate ratio, you can optimize the performance of your vehicle for different driving conditions.

2. How do I calculate the gear/sprocket ratio for my vehicle?

To calculate the gear/sprocket ratio, you will need to know the number of teeth on the gear/sprocket and the number of teeth on the corresponding gear/sprocket it is meshing with. The ratio is then calculated by dividing the number of teeth on the larger gear/sprocket by the number of teeth on the smaller gear/sprocket.

3. What factors should I consider when selecting gear/sprocket ratios?

When selecting gear/sprocket ratios, you should consider the type of vehicle, the terrain it will be driven on, and the desired speed and torque. You should also consider the power and torque of the engine, as well as the weight of the vehicle.

4. How do I know if I have selected the correct gear/sprocket ratio for my vehicle?

The best way to determine if you have selected the correct gear/sprocket ratio is to test drive your vehicle. If the vehicle is able to reach the desired speed and has enough torque for the driving conditions, then the ratio is likely appropriate. If not, you may need to adjust the ratio.

5. Can I change the gear/sprocket ratio on my vehicle?

In some cases, it is possible to change the gear/sprocket ratio on a vehicle. However, this may require replacing the existing gears/sprockets and can be a complex and expensive process. It is important to consult with a professional mechanic before attempting to change the gear/sprocket ratio on your vehicle.

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