Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

Car - Required Power and Torque

Power, torque, efficiency and wheel force acting on a car.

Sponsored Links

Engine Power

Required power from an engine to keep a car at constant speed can be calculated as

P = FT v / η                (1)

where

P = engine power (W)

FT = total forces acting on the car - rolling resistance force, gradient resistance force and aerodynamic drag resistance  (N)

v = velocity of the car (m/s)

η = overall efficiency in the transmission, normally ranging 0.85 (low gear) - 0.9 (direct drive)

For a car that accelerates the acceleration force must be added to the total force. 

Example - Car and required Engine Power

The required engine power for a car driving on a flat surface with constant speed 90 km/h with an aerodynamic resistance force 250 N and rolling resistance force 400 N and overall efficiency 0.85 - can be calculated as

P = ((250 N) + (400 N)) (90 km/h) (1000 m/km) (1/3600 h/s) / 0.85

  = 19118 W

  = 19 kW 

Engine Torque or Moment

Motor torque vs. power and rpm can be calculated

T = P / (2 π nrps)

   = 0.159 P / nrps

   = P / (2 π (nrpm / 60))

   = 9.55 P / nrpm                    (2)

where

T = torque or moment (Nm)

nrps = engine speed (rps, rev/sec)

nrpm = engine speed (rpm, rev/min)

Example - Car and required Engine Moment

The moment delivered by the motor in the car above with the engine running at speed 1500 rpm can be calculated as

T = 9.55 (19118 W) / (1500 rpm)

   = 121 Nm

Wheel Force

The total force (1) acting on the car is equal to the traction force between the driving wheels and the road surface:

Fw = FT

where

Fw = force acting between driving wheels and road surface  (N)

The traction force can be expressed with engine torque and velocity and wheels sizes and velocities:

Fw = FT

    = (T η / r) (nrps / nw_rps

   = (T η / r) (nrpm / nw_rpm)  

   = (2 T η / d) (nrpm / nw_rpm    (3)

r = wheel radius (m)

d = wheel diameter (m)

nw_rps = wheel speed (rps, rev/sec)

nw_rpm = wheel speed (rpm, rev/min)

Note that curved driving adds a centripetal force to the total force acting between the wheels and the road surface.

For power required for inclination - check car example at the end of "Forces Acting on Body Moving on an Inclined Plane".

Sponsored Links

Related Topics

Related Documents

Sponsored Links

Share

Search Engineering ToolBox

  • the most efficient way to navigate the Engineering ToolBox!

SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.

Topics

Unit Converters

Temperature

oC
oF


Load Calculator!

Length

m
km
in
ft
yards
miles
naut miles


Load Calculator!

Area

m2
km2
in2
ft2
miles2
acres


Load Calculator!

Volume

m3
liters
in3
ft3
us gal


Load Calculator!

Weight

kgf
N
lbf


Load Calculator!

Velocity

m/s
km/h
ft/min
ft/s
mph
knots


Load Calculator!

Pressure

Pa (N/m2)
bar
mm H2O
kg/cm2
psi
inches H2O


Load Calculator!

Flow

m3/s
m3/h
US gpm
cfm


Load Calculator!

3 10

This website use cookies. By continuing to browse you are agreeing to our use of cookies! Learn more