Wheels: Vehicle Road Load and Fuel Economy online calculator

Wheels: Vehicle Road Load and Fuel Economy online calculator

This online tool calculates the road load energy necessary to propel a vehicle along a selected driving cycle. It also estimates the fuel economy the vehicle would achieve for the average powertrain efficiencies you specify. You can also specify a regenerative braking efficiency if it is a hybrid vehicle.

• The background information below explains more about what this tool does and how it works.
• Consult the modeling methodology for detailed information about the vehicle equation of motion.
• See the parameter definitions for information about the terms used below.
• See the example code to see how Wheels calculates the equation of motion.

Driving cycle:	What is a driving cycle? See data in (sec, mi/hr): UDDS HFET US06 LA92 FTP NYCC 30 mi/hr 60 mi/hr See data in (sec, km/hr): ECE-ELEM ECE-EU ECE-EULP
Cd:
Frontal area:
Crr:
Curb mass:
Payload:
Rotational inertia factor:
Wheel diameter:
Air density:

Fuel heating value:
Ave. engine efficiency:
Ave. drivetrain efficiency:
Ave. regen efficiency:
Target mi/gal: Calculates the necessary engine efficiency to achieve this mi/gal for given regen and drivetrain efficiencies.	mi/gal
What would you like on your plot?	Velocity Rolling resistance power Aerodynamic drag power Braking power Inertia power Total power Cumulative rolling resistance energy Cumulative aero energy Cumulative braking energy

Background

Moving any vehicle consumes energy in the form of aerodynamic drag and rolling resistance. Energy must also be invested in inertia, some of which will be lost when the brakes are used. These losses are collectively referred to as road load, or the tractive energy demand, or the energy demanded "at the wheels".

Unfortunately, any powertrain that can deliver this energy to the wheels will lose a lot of energy on the way - primarily in thermodynamic losses in converting fuel to work, and also in transmitting the work through downstream mechanical components. You must account for these losses, too, if you want to compute fuel economy.

This tool

Wheels lets you define a vehicle by specifying its road load parameters, and then computes the total energy needed at the wheels to propel it along a specified urban or highway driving cycle. The energy usage is broken down among drag, rolling resistance, and braking.

You can also account for powertrain losses in an approximate manner by specifying the average efficiency of the engine and of the drivetrain (the transmission and other mechanical driveline components). You may also specify a regenerative braking efficiency, which represents the percentage of total braking energy successfully captured and used again (applicable only to a hybrid vehicle).

In practice, average efficiencies of the engine and other components are rarely known accurately, but are commonly estimated for modeling purposes. Even when known, they would be valid only for a specific driving cycle. The miles-per-gallon figure this tool returns is therefore not exact, but is useful for comparing the efficiency of hypothetical vehicle configurations with respect to a specific driving cycle.

Methodology

For more information, please read about the modeling methodology employed in this model. Some of the Perl code used for this simulation can also be inspected.

Disclaimer

When I couldn't find any similar tools online, I created this one by porting some of the code I wrote for my professional work. I've checked the online version against the original and it seems to give the same results. However, this version has not been extensively tested, so your mileage may vary. Contact me via Virtual Car to report bugs or questions.