Suppose your motor vehicles speedometer not working and you need to know your vehicle speed for the given engine speed for a certain gear ratio. How you can do that , let’s see..
Say, Engine rpm= 3000
Gear ratio=1.5
Axle ratio = 4
Tyre size = 12 inch radius
The formula for calculating vehicle speed is:
Car or automobile speed in consistent unit,
V = (engine rpm * wheel tyre perimeter)/(gear ratio * axle ratio)
Or, V = (engine rpm * 3.14 * tyre diameter ) / ( gear ratio * wheel axle ratio)
For the given values,
V = (3000 rpm* 3.14 * 2 * 12 inch) / ( 1.5 * 4)
Or, V (kmph)= (3000 * 60 rph * 3.14 * 2 * 12 * 25.4 * 0.000001 km)/(1.5 * 4)
Or, V = 57.42 kmph
Now as you know the equation for calculating vehicle speed given the engine rotation speed, you can easily find out the engine rpm of your car if you the vehicle speed from your speedo.
Hi, I am Shibashis, a blogger by passion and an engineer by profession. I have written most of the articles for mechGuru.com. For more than a decades i am closely associated with the engineering design/manufacturing simulation technologies. I am a self taught code hobbyist, presently in love with Python (Open CV / ML / Data Science /AWS -3000+ lines, 400+ hrs. )
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Hi I have two questions
1.What is the difference between engine speed and vehicle speed?
2.what is the difference between engine speed and engine rpm?
3. Formula to calculate engine rpm without using vehicle speed (because even when speed is zero engine will be running and engine is not dependent of vehicle speed)
1. vehicle speed is the speed at wheel, engine speed is the engine RPM transmitted after clutch
2.Engine speed = engine RPM
3. although engine run all the time but the RPM of it dont get transmitted to vehicle because of clutch
If we use this method to calculate the vehicle speed what is the necessary of wheel speed sensor in the vehicle?