Power-to-weight ratio

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Power-to-weight ratio (or specific power or power-to-mass ratio) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power source. It is also used as a measurement of performance of a vehicle as a whole, with the engine's power output being divided by the weight (or mass) of the vehicle, to give a metric that is independent of the vehicle's size. Power-to-weight is often quoted by manufacturers at the peak value, but the actual value may vary in use and variations will affect performance.

The inverse of power-to-weight, weight-to-power ratio (power loading) is a calculation commonly applied to aircraft, cars, and vehicles in general, to enable the comparison of one vehicle's performance to another. Power-to-weight ratio is equal to thrust per unit mass multiplied by the velocity of any vehicle.

Power-to-weight (specific power)[edit]

The power-to-weight ratio (Specific Power) formula for an engine (power plant) is the power generated by the engine divided by the mass. ("Weight" in this context is a colloquial term for "mass". To see this, note that what an engineer means by the "power to weight ratio" of an electric motor is not infinite in a zero gravity environment.)

A typical turbocharged V8 diesel engine might have an engine power of 330 horsepower (250 kW) and a mass of 835 pounds (379 kg),[1] giving it a power-to-weight ratio of 0.65 kW/kg (0.40 hp/lb).

Examples of high power-to-weight ratios can often be found in turbines. This is because of their ability to operate at very high speeds. For example, the Space Shuttle's main engines used turbopumps (machines consisting of a pump driven by a turbine engine) to feed the propellants (liquid oxygen and liquid hydrogen) into the engine's combustion chamber. The original liquid hydrogen turbopump is similar in size to an automobile engine (weighing approximately 775 pounds (352 kg)) and produces 72,000 hp (53.6 MW)[2] for a power-to-weight ratio of 153 kW/kg (93 hp/lb).

Physical interpretation[edit]

In classical mechanics, instantaneous power is the limiting value of the average work done per unit time as the time interval Δt approaches zero.

 P = \lim _{\Delta t\rightarrow 0} \tfrac{\Delta W(t)}{\Delta t} = \lim _{\Delta t\rightarrow 0} P_\mathrm{avg}\,

The typically used metrical unit of the power-to-weight ratio is \tfrac{W}{kg}\; which equals \tfrac{m^2}{s^3}\;. This fact allows one to express the power-to-weight ratio purely by SI base units.

Propulsive power[edit]

If the work to be done is rectilinear motion of a body with constant mass m\;, whose center of mass is to be accelerated along a straight line to a speed |\mathbf{v}(t)|\; and angle \phi\; with respect to the centre and radial of a gravitational field by an onboard powerplant, then the associated kinetic energy to be delivered to the body is equal to

 E_K =\tfrac{1}{2} m|\mathbf{v}(t)|^2

where:

m\; is mass of the body
|\mathbf{v}(t)|\; is speed of the center of mass of the body, changing with time.

The instantaneous mechanical pushing/pulling power delivered to the body from the powerplant is then

 P_K =\tfrac{1}{2} m 2|\mathbf{v}(t)| \lim _{\Delta t\rightarrow 0} \tfrac{\Delta |\mathbf{v}(t)|}{\Delta t} =  m \mathbf{a}(t) \cdot \mathbf{v}(t) = \mathbf{F}(t) \cdot \mathbf{v}(t) = \mathbf{\tau}(t) \cdot \mathbf{\omega}(t)

where:

\mathbf{a}(t)\; is acceleration of the center of mass of the body, changing with time.
\mathbf{F}(t)\; is linear force - or thrust - applied upon the center of mass of the body, changing with time.
\mathbf{v}(t)\; is velocity of the center of mass of the body, changing with time.
\mathbf{\tau}(t)\; is torque applied upon the center of mass of the body, changing with time.
\mathbf{\omega}(t)\; is angular velocity of the center of mass of the body, changing with time.

In propulsion, power is only delivered if the powerplant is in motion, and is transmitted to cause the body to be in motion. It is typically assumed here that mechanical transmission allows the powerplant to operate at peak output power. This assumption allows engine tuning to trade power band width and engine mass for transmission complexity and mass. Electric motors do not suffer from this tradeoff, instead trading their high torque for traction at low speed. The power advantage or power-to-weight ratio is then

 \mbox{P-to-W} = \frac{|\mathbf{a}(t)||\mathbf{v}(t)|}{|\mathbf{g}|}\;

where:

|\mathbf{v}(t)|\; is linear speed of the center of mass of the body.

Engine power[edit]

The actual useful power of any traction engine can be calculated using a dynamometer to measure torque and rotational speed, with peak power sustained when transmission and/or operator keeps the product of torque and rotational speed maximised. For jet engines there is often a cruise speed and power can be usefully calculated there, for rockets there is typically no cruise speed, so it is less meaningful.

Peak power of a traction engine occurs at a rotational speed higher than the speed when torque is maximised and at or below the maximum rated rotational speed - Max RPM. A rapidly falling torque curve would correspond with sharp torque and power curve peaks around their maxima at similar rotational speed, for example a small, lightweight engine with a large turbocharger. A slowly falling or near flat torque curve would correspond with a slowly rising power curve up to a maximum at a rotational speed close to Max RPM, for example a large, heavy multi-cylinder engine suitable for cargo/hauling. A falling torque curve could correspond with a near flat power curve across rotational speeds for smooth handling at different vehicle speeds.

Examples[edit]

Engines[edit]

Heat engines and heat pumps[edit]

Thermal energy is made up from molecular kinetic energy and latent phase energy. Heat engines are able to convert thermal energy in the form of a temperature gradient between a hot source and a cold sink into other desirable mechanical work. Heat pumps take mechanical work to regenerate thermal energy in a temperature gradient. Care should be made when interpreting propulsive power, especially for jet engines and rockets, deliverable from heat engines to a vehicle.

Heat Engine/Heat pump typePeak Power OutputPower-to-weight ratioExample Use
Wärtsilä RTA96-C 14-cylinder two-stroke Turbo Diesel engine[3]80,080 kW108,920 hp0.03 kW/kg0.02 hp/lbEmma Mærsk container ship
Suzuki 538 cc V2 4-stroke gas (petrol) outboard Otto engine[4]19 kW25 hp0.27 kW/kg0.16 hp/lbRunabout boats
DOE/NASA/0032-28 Mod 2 502 cc gas (petrol) Stirling engine[5]62.3 kW83.5 hp0.30 kW/kg0.18 hp/lbChevrolet Celebrity[•] 1985
GM 6.6 L Duramax LMM (LYE option) V8 Turbo Diesel engine[1]246 kW330 hp0.65 kW/kg0.40 hp/lbChevrolet Kodiak[•], GMC Topkick[•]
Junkers Jumo 205A opposed-piston two-stroke Diesel engine[6]647 kW867 hp1.1 kW/kg0.66 hp/lbJu 86C-1 airliner, B&V Ha 139 floatplane
GE LM2500+ marine turboshaft Brayton gas turbine[7]30,200 kW40,500 hp1.31 kW/kg0.80 hp/lbGTS Millennium cruiseship, QM2 ocean liner
Mazda 13B-MSP Renesis 1.3 L Wankel engine[8]184 kW247 hp1.5 kW/kg0.92 hp/lbMazda RX-8[•]
PW R-4360 71.5 L 28-cylinder supercharged Radial engine3,210 kW4,300 hp1.83 kW/kg1.11 hp/lbB-50 Superfortress, Convair B-36
C-97 Stratofreighter, C-119 Flying Boxcar
Hughes H-4 Hercules "Spruce Goose"
Wright R-3350 54.57 L 18-c s/c Turbo-compound Radial engine2,535 kW3,400 hp2.09 kW/kg1.27 hp/lbB-29 Superfortress, Douglas DC-7
C-97 S/f prototype, Kaiser-Frazer C-119F
O.S. Engines 49-PI Type II 4.97 cc UAV Wankel engine[9]0.934 kW1.252 hp2.8 kW/kg1.7 hp/lbModel aircraft, Radio-controlled aircraft
GE LM6000 marine turboshaft Brayton gas turbine[10][11][disputed ]44,700 kW59,900 hp5.67 kW/kg3.38 hp/lbPeaking power plant
GE CF6-80C2 Brayton high-bypass turbofan jet engine[11]Boeing 747[•], 767, Airbus A300
BMW V10 3L P84/5 2005 gas (petrol) Otto engine[12]690 kW925 hp7.5 kW/kg4.6 hp/lbWilliams FW27 car[•], Formula One auto racing
GE90-115B Brayton turbofan jet engine[13][14][disputed ]83,164 kW111,526 hp10.0 kW/kg6.10 hp/lbBoeing 777
PWR RS-24 (SSME) Block II H2 Brayton turbopump[15][16]63,384 kW85,000 hp138 kW/kg84 hp/lbSpace Shuttle (STS-110 and later) [•]
PWR RS-24 (SSME) Block I H2 Brayton turbopump[2]53,690 kW72,000 hp153 kW/kg93 hp/lbSpace Shuttle
  1. Full vehicle power-to-weight ratio shown below

Electric motors/Electromotive generators[edit]

An electric motor uses electrical energy to provide mechanical work, usually through the interaction of a magnetic field and current-carrying conductors. By the interaction of mechanical work on an electrical conductor in a magnetic field, electrical energy can be generated.

Electric motor typeWeightPeak Power OutputPower-to-weight ratioExample Use
Panasonic MSMA202S1G AC servo motor[17]6.5 kg14.3 lb2 kW2.7 hp0.31 kW/kg0.19 hp/lbConveyor belts, Robotics
Toshiba 660 MVA water cooled 23kV AC turbo generator1,342 t2,959,000 lb660 MW885,000 hp0.49 kW/kg0.30 hp/lbBayswater, Eraring Coal Power stations
Canopy Tech. Cypress 32 MW 15 kV AC PM generator[18]33,557 kg73,981 lb32 MW42,913 hp0.95 kW/kg0.58 hp/lbElectric Power stations
Toyota Brushless AC Nd Fe B PM motor[19]36.3 kg80.0 lb50 kW67 hp1.37 kW/kg0.84 hp/lbToyota Prius[•] 2004
Himax HC6332-250 Brushless DC motor[20]0.45 kg0.99 lb1.7 kW2.28 hp3.78 kW/kg2.30 hp/lbRadio controlled cars
Hi-Pa Drive HPD40 Brushless DC wheel hub motor[21]25 kg55.1 lb120 kW161 hp4.8 kW/kg2.92 hp/lbMini QED HEV, Ford F150 HEV
ElectriFly GPMG4805 Brushless DC[22]1.48 kg3.26 lb8.4 kW11.26 hp5.68 kW/kg3.45 hp/lbRadio-controlled aircraft
  1. Full vehicle power-to-weight ratio shown below

Fluid engines and fluid pumps[edit]

Fluids (liquid and gas) can be used to transmit and/or store energy using pressure and other fluid properties. Hydraulic (liquid) and pneumatic (gas) engines convert fluid pressure into other desirable mechanical or electrical work. Fluid pumps convert mechanical or electrical work into movement or pressure changes of a fluid, or storage in a pressure vessel.

Fluid Powerplant typeDry WeightPeak Power OutputPower-to-weight ratio
PlatypusPower Q2/200 hydroelectric turbine[23]43 kg95 lb2 kW2.7 hp0.047 kW/kg0.029 hp/lb
PlatypusPower PP20/200 hydroelectric turbine[23]330 kg728 lb20 kW27 hp0.060 kW/kg0.037 hp/lb
Atlas Copco LZL 35 pneumatic motor[24]20 kg44.1 lb6.5 kW8.7 hp0.33 kW/kg0.20 hp/lb
Atlas Copco LZB 14 pneumatic motor[25]0.30 kg0.66 lb0.16 kW0.22 hp0.53 kW/kg0.33 hp/lb
Bosch 0 607 954 307 pneumatic motor[26]0.32 kg0.71 lb0.1 kW0.13 hp0.31 kW/kg0.19 hp/lb
Atlas Copco LZB 46 pneumatic motor[27]1.2 kg2.65 lb0.84 kW1.13 hp0.7 kW/kg0.43 hp/lb
Bosch 0 607 957 307 pneumatic motor[26]1.7 kg3.7 lb0.74 kW0.99 hp0.44 kW/kg0.26 hp/lb
SAI GM7 radial piston hydraulic motor[28]300 kg661 lb250 kW335 hp0.83 kW/kg0.50 hp/lb
SAI GM3 radial piston hydraulic motor[29]15 kg33 lb15 kW20 hp1 kW/kg0.61 hp/lb
Denison GOLD CUP P14 axial piston hydraulic motor[30]110 kg250 lb384 kW509 hp3.5 kW/kg2.0 hp/lb
Denison TB vane pump[31]7 kg15 lb40.2 kW53.9 hp5.7 kW/kg3.6 hp/lb

Thermoelectric generators and electrothermal actuators[edit]

A variety of effects can be harnessed to produce thermoelectricity, thermionic emission, pyroelectricity and piezoelectricity. Electrical resistance and ferromagnetism of materials can be harnessed to generate thermoacoustic energy from an electric current.

Thermoelectric Powerplant typeDry WeightPeak Power OutputPower-to-weight ratioExample Use
Teledyne 238Pu GPHS-RTG 1980[32][33]56 kg123 lb285 W0.39 hp5.09 W/kg0.003 hp/lbGalileo probe, New Horizons probe
Boeing 238Pu MMRTG MSL[33]44.1 kg97.2 lb123 W0.16 hp2.79 W/kg0.002 hp/lbMars Science Laboratory
HZ-20 thermoelectric module0.115 kg0.254 lb19 W0.025 hp165 W/kg0.098 hp/lbHi-Z Technology Inc.

Electrochemical (galvanic) and electrostatic cell systems[edit]

(Closed cell) batteries[edit]

All electrochemical cell batteries deliver a changing voltage as their chemistry changes from "charged" to "discharged". A nominal output voltage and a cutoff voltage are typically specified for a battery by its manufacturer. The output voltage falls to the cutoff voltage when the battery becomes "discharged". The nominal output voltage is always less than the open-circuit voltage produced when the battery is "charged". The temperature of a battery can affect the power it can deliver, where lower temperatures reduce power. Total energy delivered from a single charge cycle is affected by both the battery temperature and the power it delivers. If the temperature lowers or the power demand increases, the total energy delivered at the point of "discharge" is also reduced.

Battery discharge profiles are often described in terms of a factor of battery capacity. For example a battery with a nominal capacity quoted in ampere-hours (Ah) at a C/10 rated discharge current (derived in amperes) may safely provide a higher discharge current - and therefore higher power-to-weight ratio - but only with a lower energy capacity. Power-to-weight ratio for batteries is therefore less meaningful without reference to corresponding energy-to-weight ratio and cell temperature. This relationship is known as Peukert's law.[34]

Battery typeVoltsTemp.Energy-to-weight ratioPower-to-weight ratio
Energizer 675 Mercury Free Zinc-air battery[35]1.4V21 °C1,645 kJ/kg to 0.9 V1.65 W/kg 2.24 mA
GE Durathon™ NaMx A2 UPS Molten salt battery[36]54.2V-40–65°C342 kJ/kg to 37.8 V15.8 W/kg C/6 (76 A)
Panasonic R03 AAA Zinc–carbon battery[37][38]1.5 V20±2 °C47 kJ/kg 20 mA to 0.9 V3.3 W/kg 20 mA
88 kJ/kg 150 mA to 0.9 V24 W/kg 150 mA
Eagle-Picher SAR-10081 60Ah 22-cell Nickel–hydrogen battery[39]27.7 V10 °C192 kJ/kg C/2 to 22 V23 W/kg C/2
165 kJ/kg C/1 to 22 V46 W/kg C/1
ClaytonPower 400Ah Lithium-ion battery[40][41]12V617 kJ/kg85.7 W/kg C/1 (175 A)
Energizer 522 Prismatic ZnMnO2 Alkaline battery[42]9 V21 °C444 kJ/kg 25 mA to 4.8 V4.9 W/kg 25 mA
340 kJ/kg 100 mA to 4.8 V19.7 W/kg 100 mA
221 kJ/kg 500 mA to 4.8 V99 W/kg 500 mA
Panasonic HHR900D 9.25Ah Nickel–metal hydride battery[43]1.2 V20 °C209.65 kJ/kg to 0.7 V11.7 W/kg C/5
58.2 W/kg C/1
116 W/kg 2C
URI 1418Ah replaceable anode Aluminium–air battery model[44][45]244.8 V60 °C4680 kJ/kg130.3 W/kg (142 A)
LG Chemical/CPI E2 6Ah LiMn2O4 Lithium-ion polymer battery[46][47]3.8 V25 °C530.1 kJ/kg C/2 to 3.0 V71.25 W/kg
513 kJ/kg 1C to 3.0 V142.5 W/kg
Saft 45E Fe Super-Phosphate Lithium iron phosphate battery[48]3.3 V25 °C581 kJ/kg C to 2.5 V161 W/kg
560 kJ/kg 1.14 C to 2.0 V183 W/kg
0.73 kJ/kg 2.27 C to 1.5 V367 W/kg
Energizer CH35 C 1.8Ah Nickel–cadmium battery[49]1.2 V21 °C152 kJ/kg C/10 to 1 V4 W/kg C/10
147.1 kJ/kg 5C to 1 V200 W/kg 5 C
Firefly Energy Oasis FF12D1-G31 6-cell 105Ah VRLA battery[50]12 V25 °C142 kJ/kg C/10 to 7.2 V4 W/kg C/10
-1 8 °C7 kJ/kg CCA to 7.2V234 W/kg CCA (625A)
0 °C9 kJ/kg CA to 7.2 V300 W/kg CA (800 A)
Panasonic CGA103450A 1.95Ah LiCoO2 Lithium-ion battery[51]3.7 V20 °C666 kJ/kg C/5.3 to 2.75 V35 W/kg C/5.3
0 °C633 kJ/kg C/1 to 2.75 V176 W/kg C/1
20 °C655 kJ/kg C/1 to 2.75 V182 W/kg C/1
20 °C641 kJ/kg 2C to 2.75 V356 W/kg 2C
Electric Fuel Battery Corp. UUV 120Ah Zinc–air fuel cell[52]630 kJ/kg500 W/kg C/1
Sion Power 2.5Ah Li–S Lithium-ion battery[53]2.15 V25 °C1260 kJ/kg70 W/kg C/5
1209 kJ/kg672 W/kg 2C
Maxell / Yuasa / AIST Nickel–metal hydride lab prototype[54]45 °C980 W/kg
Toshiba SCiB cell 4.2Ah Li2TiO3 Lithium-ion battery[55][56]2.4 V25 °C242 kJ/kg67.2 W/kg C/1
218 kJ/kg4000 W/kg 12C
Ionix Power Systems LiMn2O4 Lithium-ion battery lab model[57]lab270 kJ/kg1700 W/kg
lab29 kJ/kg4900 W/kg
A123 Systems 26650 Cell 2.3Ah LiFePO4 Lithium ion battery[58][59]3.3 V-20 °C347 kJ/kg C/1 to 2V108 W/kg C/1
0 °C371 kJ/kg C/1 to 2 V108 W/kg C/1
25 °C390 kJ/kg C/1 to 2 V108 W/kg C/1
25 °C390 kJ/kg 27C to 2 V3300 W/kg 27C
25 °C57 kJ/kg 32C to 2 V5657 W/kg 32C
Saft VL 6Ah Lithium-ion battery[60]3.65 V-20 °C154 kJ/kg 30C to 2.5 V41.4 W/kg 30C (180 A)
182 kJ/kg 1C to 2.5 V67.4 W/kg 1C
25 °C232 kJ/kg 1C to 2.5 V64.4 W/kg 1C
233 kJ/kg 58.3C to 2.5 V3757 W/kg 58.3C (350A)
34 kJ/kg 267C to 2.5 V17176 W/kg 267C (1.6kA)
4.29 kJ/kg 333C to 2.5 V21370 W/kg 333C (2kA)

Electrostatic, electrolytic and electrochemical capacitors[edit]

Capacitors store electric charge onto two electrodes separated by an electric field semi-insulating (dielectric) medium. Electrostatic capacitors feature planar electrodes onto which electric charge accumulates. Electrolytic capacitors use a liquid electrolyte as one of the electrodes and the electric double layer effect upon the surface of the dielectric-electrolyte boundary to increase the amount of charge stored per unit volume. Electric double-layer capacitors extend both electrodes with a nanopourous material such as activated carbon to significantly increase the surface area upon which electric charge can accumulate, reducing the dielectric medium to nanopores and a very thin high permittivity separator.

While capacitors tend not to be as temperature sensitive as batteries, they are significantly capacity constrained and without the strength of chemical bonds suffer from self-discharge. Power-to-weight ratio of capacitors is usually higher than batteries because charge transport units within the cell are smaller (electrons rather than ions), however energy-to-weight ratio is conversely usually lower.

Capacitor typeCapacityVoltsTemp.Energy-to-weight ratioPower-to-weight ratio
ACT Premlis Lithium ion capacitor[61]2000 F4.0 V25 °C54 kJ/kg to 2.0 V44.4 W/kg @ 5 A
31 kJ/kg to 2.0 V850 W/kg @ 10 A
Nesccap Electric double-layer capacitor[62]5000 F2.7 V25 °C19.58 kJ/kg to 1.35 V5.44 W/kg C/1 (1.875 A)
5.2 kJ/kg to 1.35 V5,200 W/kg[63] @ 2,547A
EEStor EESU barium titanate supercapacitor[64]30.693 F3500 V85 °C1471.98 kJ/kg80.35 W/kg C/5
1471.98 kJ/kg8,035 W∕kg 20 C
General Atomics 3330CMX2205 High Voltage Capacitor[65]20.5 mF3300 V ? °C2.3 kJ/kg6.8 MW/kg @ 100 kA

Fuel cell stacks and flow cell batteries[edit]

Fuel cells and flow cells, although perhaps using similar chemistry to batteries, have the distinction of not containing the energy storage medium or fuel. With a continuous flow of fuel and oxidant, available fuel cells and flow cells continue to convert the energy storage medium into electric energy and waste products. Fuel cells distinctly contain a fixed electrolyte whereas flow cells also require a continuous flow of electrolyte. Flow cells typically have the fuel dissolved in the electrolyte.

Fuel cell typeDry weightPower-to-weight ratioExample Use
Redflow Power+BOS ZB600 10kWh ZBB[66]900 kg5.6 W/kg (9.3 W/kg peak)Rural Grid support
Ceramic Fuel Cells BlueGen MG 2.0 CHP SOFC[67]200 kg10 W/kg
15 W/kg CHP
MTU Friedrichshafen 240 kW MCFC HotModule 200620 t12 W/kg
Smart Fuel Cell Jenny 600S 25W DMFC[68]1.7 kg14.7 W/kgPortable military electronics
UTC Power PureCell 400 kW PAFC[69]27,216 kg14.7 W/kg
GEFC 50V50A-VRB Vanadium redox battery[70]80 kg31.3 W/kg (125 W/kg peak)
Ballard Power Systems Xcellsis HY-205 205 kW PEMFC[71]2,170 kg94.5 W/kgMercedes-Benz Citaro O530BZ[•]
UTC Power/NASA 12 kW AFC[72]122 kg98 W/kgSpace Shuttle orbiter[•]
Ballard Power Systems FCgen-1030 1.2 kW CHP PEMFC[73]12 kg100 W/kgResidential cogeneration
Ballard Power Systems FCvelocity-HD6 150 kW PEMFC[73]400 kg375 W/kgBus and heavy duty
Honda 2003 43 kW FC Stack PEMFC[74][•]43 kg1000 W/kgHonda FCX Clarity[•]
Lynntech, Inc. PEMFC lab prototype[75]347 g1,500 W/kg
  1. Full vehicle power-to-weight ratio shown below

Photovoltaics[edit]

Photovoltaic Panel typePower-to-weight ratio
Thyssen Solartec 128W Nanocrystalline Si Triplejunction PV module[76]6 W/kg
Suntech/UNSW HiPerforma PLUTO220-Udm 220W Ga-F22 Polycrystalline Si PV module[77]13.1 W/kg STP
9.64 W/kg nominal
Global Solar PN16015A 62W CIGS polycrystalline thin film PV module[78]40 W/kg
Able (AEC) PUMA 6 kW GaInP2/GaAs/Ge-on-Ge Triplejunction PV array[79]65 W/kg
Current spacecraft grade~77 W/kg[80]
ITO/InP on Kapton foil2000 W/kg[81]

Vehicles[edit]

Power-to-weight ratios for vehicles are usually calculated using Curb weight (for cars) or wet weight (for motorcycles) – in other words, excluding weight of the driver and any cargo. This could be slightly misleading, especially with regard to motorcycles, where the driver might weigh 1/3 to 1/2 as much as the vehicle itself. In the sport of competitive cycling athlete's performance is increasingly being expressed in VAMs and thus as a power-to-weight ratio in W/kg. This can be measured through the use of a bicycle powermeter or calculated from measuring incline of a road climb and the rider's time to ascend it.[82]

Utility and practical vehicles[edit]

Most vehicles are designed to meet passenger comfort and cargo carrying requirements. Different designs trade off power-to-weight ratio to increase comfort, cargo space, fuel economy, emissions control, energy security and endurance. Reduced drag and lower rolling resistance in a vehicle design can facilitate increased cargo space without increase in the (zero cargo) power-to-weight ratio. This increases the role flexibility of the vehicle. Energy security considerations can trade off power (typically decreased) and weight (typically increased), and therefore power-to-weight ratio, for fuel flexibility or drive-train hybridisation. Some utility and practical vehicle variants such as hot hatches and sports-utility vehicles reconfigure power (typically increased) and weight to provide the perception of sports car like performance or for other psychological benefit. Rail locomotives require high mass to maintain adhesive traction on the rails, therefore improving the power-to-weight ratio by reducing mass is not necessarily beneficial. However choice of rail locomotive traction system (i.e. AC VFD over DC) can support improved power-to-weight ratio by reducing mass for the same adhesion.

Notable low ratio, (listed as weight to power)[edit]
VehiclePowerWeightWeight to Power ratio
Benz Patent Motorwagen 954 cc 1886[83]560 W / 0.75 bhp265 kg / 584 lb2.1 W/kg / 779 lb/hp
Stephenson's Rocket 0-2-2 steam locomotive with tender 1829[84]15 kW / 20 bhp4,320 kg / 9524 lb3.5 W/kg / 476 lb/hp
CBQ Zephyr streamliner diesel locomotive with railcars 1934[85]492 kW / 660 bhp94 t / 208,000 lb5.21 W/kg / 315 lb/hp
Alberto Contador's Verbier climb 2009 Tour de France on Specialized bike[82]420 W / 0.56 bhp62 kg / 137 lb6.7 W/kg / 245 lb/hp
Force Motors Minidor Diesel 499 cc auto rickshaw[86][87]6.6 kW / 8.8 bhp700 kg / 1543 lb9 W/kg / 175 lb/hp
PRR Q2 4-4-6-4 steam locomotive with tender 19445,956 kW / 7,987 bhp475.9 t / 1,049,100 lb12.5 W/kg / 131 lb/hp
Mercedes-Benz Citaro O530BZ H2 fuel cell bus 2002[88]205 kW / 275 bhp14,500 kg / 32,000 lb14.1 W/kg / 116 lb/hp
TGV BR Class 373 high-speed Eurostar Trainset 199312,240 kW / 16,414 bhp816 t / 1,798,972 lb15 W/kg / 110 lb/hp
General Dynamics M1 Abrams Main battle tank 1980[89]1,119 kW / 1500 bhp55.7 t / 122,800 lb20.1 W/kg / 81.9 lb/hp
BR Class 43 high-speed diesel electric locomotive 19751,678 kW / 2,250 bhp70.25 t / 154,875 lb23.9 W/kg / 69 lb/hp
GE AC6000CW diesel electric locomotive 19964,660 kW / 6,250 bhp192 t / 423,000 lb24.3 W/kg / 68 lb/hp
BR Class 55 Napier Deltic diesel electric locomotive 19612,460 kW / 3,300 bhp101 t / 222,667 lb24.4 W/kg / 68 lb/hp
International CXT 2004[90]164 kW / 220 bhp6,577 kg / 14500 lb25 W/kg / 66 lb/hp
Ford Model T 2.9 L flex-fuel 190815 kW / 20 bhp540 kg / 1,200 lb28 W/kg / 60 lb/hp
TH!NK City 2008[91]30 kW / 40 bhp1038 kg / 2,288 lb28.9 W/kg / 56.9 lb/hp
Messerschmitt KR200 Kabinenroller 191 cc 19556 kW / 8.2 bhp230 kg / 506 lb30 W/kg / 50 lb/hp
Wright Flyer 19039 kW / 12 bhp274 kg / 605 lb33 W/kg / 50 lb/hp
Tata Nano 624 cc 200826 kW / 35 bhp635 kg / 1,400 lb41.0 W/kg / 40 lb/hp
Bombardier JetTrain high-speed gas turbine-electric locomotive 2000[92]3,750 kW / 5,029 bhp90,750 kg / 200,000 lb41.2 W/kg / 39.8 lb/hp
Suzuki MightyBoy 543 cc 198823 kW / 31 bhp550 kg / 1,213 lb42 W/kg / 39 lb/hp
Mitsubishi i MiEV 2009[93]47 kW / 63 bhp1,080 kg / 2,381 lb43.5 W/kg / 37.8 lb/hp
Holden FJ 2,160 cc 1953[94]44.7 kW / 60 bhp1,021 kg / 2,250 lb43.8 W/kg / 37.5 lb/hp
Chevrolet Kodiak/GMC Topkick LYE 6.6 L 2005[1][95]246 kW / 330 bhp5126 kg / 11,300 lb48 W/kg / 34.2 lb/hp
DOE/NASA/0032-28 Chevrolet Celebrity 502 cc ASE Mod II 1985[5]62.3 kW / 83.5 bhp1,297 kg / 2,860 lb48.0 W/kg / 34.3 lb/hp
Suzuki Alto 796 cc 200035 kW / 46 bhp720 kg / 1,587 lb49 W/kg / 35 lb/hp
Land Rover Defender 2.4 L 1990[96]90 kW / 121 bhp1,837 kg / 4,050 lb49 W/kg / 33 lb/hp
Common power, (Listed as weight to power)[edit]
VehiclePowerWeightWeight-to-Power ratio
Toyota Prius 1.8 L 2010 (petrol only)[97]73 kW / 98 bhp1,380 kg / 3,042 lb53 W/kg / 31 lb/hp
Bajaj Platina Naked 100 cc 2006[98]6 kW / 8 bhp113 kg / 249 lb53 W/kg / 31 lb/hp
Subaru R2 type S 2003[99]47 kW / 63 bhp830 kg / 1,830 lb57 W/kg / 29 lb/hp
Ford Fiesta ECOnetic 1.6 L TDCi 5dr 2009[100]66 kW / 89 bhp1,155 kg / 2,546 lb57 W/kg / 29 lb/hp
Volvo C30 1.6D DRIVe S/S 3dr Hatch 2010[101]80 kW / 108 bhp1,347 kg / 2,970 lb59.4 W/kg / 27.5 lb/hp
Ford Focus ECOnetic 1.6 L TDCi 5dr Hatch 2009[102]81 kW / 108 bhp1,357 kg / 2,992 lb59.7 W/kg / 27 lb/hp
Ford Focus 1.8 L Zetec S TDCi 5dr Hatch 2009[103]84 kW / 113 bhp1,370 kg / 3,020 lb61 W/kg / 27 lb/hp
Honda FCX Clarity 4 kg Hydrogen 2008[104]100 kW / 134 bhp1,600 kg / 3,528 lb63 W/kg / 26 lb/hp
Hummer H1 6.6 L V8 2006[105]224 kW / 300 bhp3,559 kg / 7,847 lb63 W/kg / 26 lb/hp
Audi A2 1.4 L TDI 90 type S 2003[106]66 kW / 89 bhp1,030 kg / 2,270 lb64 W/kg / 25 lb/hp
Opel/Vauxhall/Holden/Chevrolet Astra 1.7 L CTDi 125 2010[107]92 kW / 123 bhp1,393 kg / 3,071 lb66 W∕kg / 24.9 lb∕hp
Mini (new) Cooper 1.6D 2007[108]81 kW / 108 bhp1,185 kg / 2,612 lb68 W/kg / 24 lb/hp
Toyota Prius 1.8 L 2010 (electric boost)[97]100 kW / 134 bhp1,380 kg / 3,042 lb72 W/kg / 23 lb/hp
Ford Focus 2.0 L Zetec S TDCi 5dr Hatch 2009[109]100 kW / 134 bhp1,370 kg / 3,020 lb73 W/kg / 23 lb/hp
General Motors EV1 electric car Gen II 1998[110]102.2 kW / 137 bhp1,400 kg / 3,086 lb73 W/kg / 23 lb/hp
Toyota Venza I4 2.7 L FWD 2009[111]136 kW / 182 bhp1,706 kg / 3,760 lb80 W/kg / 20.7 lb/hp
Ford Focus 2.0 L Zetec S 5dr Hatch 2009[112]107 kW / 143 bhp1,327 kg / 2,926 lb81 W/kg / 20 lb/hp
Fiat Grande Punto 1.6 L Multijet 120 2005[113]88 kW / 118 bhp1,075 kg / 2,370 lb82 W/kg / 20 lb/hp
Mini (classic) 1275GT 196957 kW / 76 bhp686 kg / 1,512 lb83 W/kg / 20 lb/hp
Opel/Vauxhall/Holden/Chevrolet Astra 2.0 L CTDi 160 2010[114]118 kW / 158 bhp1,393 kg / 3,071 lb85 W∕kg / 19.4 lb∕hp
Ford Focus 2.0 auto 2007[115]104.4 kW / 140 bhp1,198 kg / 2,641 lb87.1 W/kg / 19 lb/hp
Subaru Legacy/Liberty 2.0R 2005[116]121 kW / 162 bhp1,370 kg / 3,020 lb88 W/kg / 19 lb/hp
Subaru Outback 2.5i 2008[117]130.5 kW / 175 bhp1,430 kg / 3,153 lb91 W/kg / 18 lb/hp
Smart Fortwo 1.0 L Brabus 2009[118]72 kW / 97 bhp780 kg / 1,720 lb92 W/kg / 18 lb/hp
Toyota Venza V6 3.5 L AWD 2009[111]200 kW / 268 bhp1,835 kg / 4,045 lb109 W/kg / 15 lb/hp
Toyota Venza I4 2.7 L FWD 2009[111] with Lotus mass reduction[119]136 kW / 182 bhp1,210 kg / 2,667 lb112.2 W/kg / 14.7 lb/hp
Toyota Hilux V6 DOHC 4 L 4×2 Single Cab Pickup ute 2009[120]175 kW / 235 bhp1,555 kg / 3,428 lb112.5 W/kg / 14.6 lb/hp
Toyota Venza V6 3.5 L FWD 2009[111]200 kW / 268 bhp1,755 kg / 3,870 lb114 W/kg / 14.4 lb/hp
Performance luxury, roadsters and mild sports, (Listed as weight to power)[edit]

Increased engine performance is a consideration, but also other features associated with luxury vehicles. Longitudinal engines are common. Bodies vary from hot hatches, sedans (saloons), coupés, convertibles and roadsters. Mid-range dual-sport and cruiser motorcycles tend to have similar power-to-weight ratios.

VehiclePowerWeightWeight-to-power ratio
Honda Accord sedan V6 2011202 kW / 271 bhp1630 kg / 3593 lb124 W/kg / 13.26 lb/hp
Mini (new) Cooper 1.6T S JCW 2008[121]155 kW / 208 bhp1205 kg / 2657 lb129 W/kg / 13 lb/hp
Mazda RX-8 1.3 L Wankel 2003173 kW / 232 bhp1309 kg / 2888 lb141 W/kg / 12 lb/hp
Holden Statesman/Caprice / Buick Park Avenue / Daewoo Veritas 6 L V8 2007[122]270 kW / 362 bhp1891 kg / 4170 lb143 W/kg / 12 lb/hp
Kawasaki KLR650 Gasoline DualSport 650 cc26 kW / 35 bhp182 kg / 401 lb143 W/kg / 11 lb/hp
NATO HTC M1030M1 Diesel/Jet fuel DualSport 670 cc[123]26 kW / 35 bhp182 kg / 401 lb143 W/kg / 11 lb/hp
Harley-Davidson FLSTF Softail Fat Boy Cruiser 1,584 cc 2009[124]47 kW / 63 bhp324 kg / 714 lb145 W/kg / 11.3 lb/hp
BMW 7 Series 760Li 6 L V12 2006[125]327 kW / 439 bhp2250 kg / 4960 lb145 W/kg / 11 lb/hp
Subaru Impreza WRX STi 2.0 L 2008[126]227 kW / 304 bhp1530 kg / 3373 lb148 W/kg / 11 lb/hp
Honda S2000 roadster 1999[citation needed]183.88 kW / 240 bhp1250 kg / 2723 lb150 W/kg / 11 lb/hp
GMH HSV Clubsport / GMV VXR8 / GMC CSV CR8 / Pontiac G8 6 L V8 2006[127]317 kW / 425 bhp1831 kg / 4037 lb173 W/kg / 9.5 lb/hp
Tesla Roadster 2011[128]215 kW / 288 bhp1235 kg / 2723 lb174 W/kg / 9.5 lb/hp

Sports vehicles and aircraft, (Listed as weight to power)[edit]

Power-to-weight ratio is an important vehicle characteristic that affects the acceleration and handling - and therefore the driving enjoyment - of any sports vehicle. Aircraft also depend on high power-to-weight ratio to achieve sufficient lift.

VehiclePowerWeightWeight-to-power ratio
Lotus Elise SC 2008163 kW / 218 bhp910 kg / 2006 lb179 W/kg / 9 lb/hp
Ferrari Testarossa 1984291 kW / 390 bhp1506 kg / 3320 lb193 W/kg / 9 lb/hp
Artega GT[129]220 kW / 300 bhp1100 kg / 2425 lb200 W/kg / 8 lb/hp
Lotus Exige GT3 2006[130]202.1 kW / 271 bhp980 kg / 2160 lb206 W/kg / 8 lb/hp
Chevrolet Corvette C6[131]321 kW / 430 bhp1441 kg / 3177 lb223 W/kg / 7 lb/hp
Suzuki V-Strom 650 V-twin DualSport 650 cc50 kW / 67 bhp194 kg / 427 lb258 W/kg / 6.4 lb/hp
Chevrolet Corvette C6 Z06[131]376 kW / 505 bhp1421 kg / 3133 lb265 W/kg / 6.2 lb/hp
Porsche 911 GT2 2007390 kW / 523 bhp1440 kg / 3200 lb271 W/kg / 6.1 lb/hp
Lamborghini Murciélago LP 670-4 SV 2009[132]493 kW / 661 bhp1550 kg / 3417 lb318 W/kg / 5.1 lb/hp
McLaren F1 GT 1997[133]467.6 kW / 627 bhp1220 kg / 2690 lb403 W/kg / 4.3 lb/hp
Bombardier Dash 8 Q400 turboprop airliner[134]7,562 kW / 10,142 bhp17,185 kg / 37,888 lb440 W/kg / 3.7 lb/hp
Supermarine Spitfire Fighter aircraft 19361,096 kW / 1,470 bhp2,309 kg / 5,090 lb475 W/kg / 3.46 lb/hp
Messerschmitt Bf 109 Fighter aircraft 19351,085 kW / 1,455 bhp2,247 kg / 4,954 lb483 W/kg / 3.40 lb/hp
Thunderbolt Land speed record car3504 kW / 4700 bhp7 t / 15432 lb500 W/kg / 3.28 lb/hp
Ferrari FXX 2005597 kW / 801 bhp1155 kg / 2546 lb517 W/kg / 3.2 lb/hp
Polaris Industries Assault Snowmobile 2009[135]115 kW / 154 bhp221 kg / 487 lb523 W/kg / 3.16 lb/hp
Ultima GTR 720 2006[136]536.9 kW / 720 bhp920 kg / 2183 lb583 W/kg / 3 lb/hp
Honda CBR1000RR 2009133 kW / 178 bhp199 kg / 439 lb668 W/kg / 2.5 lb/hp
Ariel Atom 500 V8 2011372 kW / 500 bhp550 kg / 1212 lb676.3 W/kg / 2.45 lb/hp
Peugeot 208 T16 Pikes Peak 2013652 kW / 875 bhp875 kg / 1930 lb745 W/kg / 2.2 lb/hp
KillaCycle Drag racing electric motorcycle260 kW / 350 bhp281 kg / 619 lb925 W/kg / 1.77 lb/hp
MTT Turbine Superbike 2008[137]213.3 kW / 286 bhp227 kg / 500 lb940 W/kg / 1.75 lb/hp
Vyrus 987 C3 4V V supercharged motorcycle 2010[138]157.3 kW / 211 bhp158 kg / 348.3 lb996 W/kg / 1.65 lb/hp
BMW Williams FW27 Formula One 2005[139]690 kW / 925 bhp600 kg / 1323 lb1150 W/kg / 1.43 lb/hp
Honda RC211V MotoGP 2004-6176.73 kW / 237 bhp148 kg / 326 lb1194 W/kg / 1.37 lb/hp
Boeing 747-300[10] at Mach 0.84 cruise, 35,000 ft altitude[disputed ]245 MW / 328,656 bhp178.1 t / 392,800 lb1376 W/kg / 1.20 lb/hp
John Force Racing Funny Car NHRA Drag Racing 2008[140]5,963.60 kW / 8,000 bhp1043 kg / 2,300 lb5717 W/kg / 0.30 lb/hp

See also[edit]

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