# Power to weight ratio

The power -to-weight ratio (also mass-performance ratio ) is the quotient of the mass and the power of a vehicle , an engine , a battery , a machine or for humans and animals. It is usually given in kilograms per kilowatt.

The reciprocal value is the power density , also called “specific power”, in kilowatts per kilogram. Both terms are sometimes referred to area or volume instead of weight. The term performance indicator is also used in the railway sector and is usually given in kilowatts per ton.

In the case of drives , a low power-to-weight ratio is generally sought, since a smaller mass or a higher power enables higher acceleration and thus counteraction to obstructive natural forces such as inertia , gravity or the moment of inertia . For example, a lower power-to-weight ratio of a vehicle allows a higher speed on inclines.

A low mass-performance ratio is also aimed for in accumulators for traction or for transportable devices; However, the stored energy per mass (joules per kilogram) usually plays a role here and should be as high as possible. See also energy density .

## Examples and meaning on vehicles

### Motor vehicles

The acceleration typically specified for motor vehicles , for example in "X seconds from 0 to 100 km / h", depends on a number of parameters (such as torque curve , gearshift , traction , air resistance ) and can therefore not be derived directly from the power to weight ratio. Basically, however, the following applies here: a lower power-to-weight ratio enables greater acceleration.

For trucks, buses and similar vehicles, minimum engine power based on weight is prescribed under German law, and consequently a maximum power-to-weight ratio.

Typical power weights in motor vehicles:

• Formula 1 car: 1 kg / kW
• GP motorcycle: 0.8 kg / kW (with driver, as of 2012)
• Sports motorcycle: 1.3 kg / kW (with driver, as of 2019)
• Sports car: 4.2 kg / kW ( Porsche 911 Turbo S , 2009)
• Common cars: 14.7 kg / kW
• Leopard 2 tank : 56 kg / kW
• Last tricycle Goliath Goli , fully loaded 164 kg / kW

Selection of some vehicles:

vehicle Empty weight
in kg
Power
in PS (bhp)
Power-
to-weight ratio in kg / PS (bhp)
Keating Bolt (Biturbo) 990 2,534.6 (2,500) 0.39 (0.40)
Keating TKR 995 2,027.7 (2000) 0.49 (0.50)
F1 Benetton B186 BMW (1986) 540 900 0.67
F1 Red Bull Racing RB8 Renault (2012) 640 750 + 80 0.89
Motorcycle Ducati 1299 Superleggera 162 220 0.76
Porsche 956 C (1984) 820 620 1.32
VW Golf VII GTI 1351 220 6.28
VW Golf I GTI 810 110 7.36
VW Polo V 1100 105 10.48
Motorbike MZ ETZ 125 120 10.2 12
Opel Corsa D 1.2 ecoFLEX 1120 70 16
Simson S51 moped 78.5 3.7 21st

With light vehicles, the weight of the people being transported is becoming more important.

### Rail vehicles

The tensile force typically specified for rail vehicles in kN or acceleration in m / s² depends on a number of parameters (e.g. torque curve , rail conditions ( slip ), traction , air resistance ) and can therefore not be derived directly from the power-to-weight ratio. Basically, however, the following applies here: A lower power-to-weight ratio enables greater acceleration, greater excess tractive power on inclines and a higher top speed.

Particularly in the case of locomotives that are supposed to pull non-powered wagons , however, a high weight is necessary so that the locomotive has high static friction on the rail. High performance with low weight would only lead to spinning wheels.

#### Examples of electric multiple units (Germany)

##### Long-distance transport
vehicle Mass 1 in kg Power 2 in kW Power to weight ratio in kg / kW Performance indicator in kW / t
ICE T 273,000-368,000 3000-4000 91.00-92.00 10.87-10.99
ICE 1 849,000 9600 88.44 11.31
ICE 2 412,000 4800 85.83 11.65
ICE 4 670,000 9900 67.68 14.78
ICE 3 409,000-454,000 8000 51.13-56.75 17.62-19.56
##### Regional traffic
vehicle Mass 1 in kg Power 2 in kW Power to weight ratio in kg / kW Performance indicator in kW / t
Stadler Kiss 170,100 - 305,000 3 2000-4500 56.70-68.60 14.58-17.64
Stadler flirt 100,000 - 170,000 1300-2600 38.46-65.38 15.29-26.00
Siemens Desiro HC 200,000 3290 4 60.79 16.45
Alstom Coradia Continental 141,000 - 168,000 2160 - 2880 4 48.96-58.33 17.14-20.43
Bombardier Talent 2 85,000 - 173,000 3 2020 - 3030 4 42.08 - 57.10 17.51-23.76
Siemens Desiro ML 132,000 2600 4 50.77 19.70
##### Train
vehicle Mass 1 in kg Power 2 in kW Power to weight ratio in kg / kW Performance indicator in kW / t
DB class 481 (2-part)
(S-Bahn Berlin)
59,000 594 4 99.33 10.07
DB class 472 (3-part)
(S-Bahn Hamburg)
114,400 1500 4 76.27 13.11
DB class 420 (3-part)
(S-Bahn Munich old)
129,000 2400 4 53.75 18.60
DB class 430 (4 parts)
(S-Bahn Stuttgart)
118,800 2350 4 50.55 19.78
DB class 425 (4 parts)
(S-Bahn Hanover)
114,000 2350 4 48.51 20.61
DB class 423 (4-part)
(S-Bahn Munich new)
105,000 2350 4 44.68 22.38

#### Examples of combustion engine railcars (Germany)

vehicle Mass 1 in kg Power 2 in kW Power to weight ratio in kg / kW Performance indicator in kW / t
Regioswinger (611) 116,000 3 1080 107.41 9.31
Regioswinger (612) 116,000 3 1120 103.57 9.66
Pendolino (610) 95,350 3 970 98.30 10.17
ICE TD 219,000 2240 97.77 10.23

#### Footnotes

1 - unless otherwise stated, the empty weight without passengers; 2 - unless otherwise specified, the maximum traction power; 3 - service mass; 4 - hourly output

### Planes

In the case of aircraft , a low mass-performance ratio or high thrust-to-weight ratio means higher climbing performance and a shorter take-off taxi distance .
Aircraft with a low power-to-weight ratio, in particular combat aircraft , can also fly long-lasting, tight turns with high g-forces , as the
drag caused by the high lift (which is necessary to overcome the centrifugal force ) is countered by a large thrust ( curve combat ). For this reason, aircraft have a particularly low power-to-weight ratio; Fighter aircraft are often also equipped with afterburners , booster engines or launchers in order to be able to increase the thrust for a short time. A thrust-to-weight ratio that is greater than 1 enables acceleration in a vertical climb.

## Examples and meaning on engines

For engines, the power-to-weight ratio is given with and without gearbox, clutch, cooler, etc. In the case of piston engines, often also the calculated power-to-weight ratio per cylinder. Selection of some internal combustion engines with a wide range of performance:

### Piston engines

engine Working principle Rotation frequency
in 1 / min
Dimensions Power
in kW
Power density
in kW / kg
Power
to weight ratio in kg / kW
cylinder Power
per cylinder
in kW
G95ME-C9 Two-stroke diesel 70-80 2400 t 82440 0.034 29.1 12 6870
G40ME-C9 Two-stroke diesel 125 173 t 8800 0.051 19.7 8th 1100
S30ME-B9 Two-stroke diesel 150 86 t 5120 0.060 16.8 8th 640
V48 / 60B Four-stroke diesel 500 250 t 20700 0.083 12.1 18th 1150
L21 / 31 Four-stroke diesel 1000 20 t 2000 0.100 10.0 9 222
DENQBAR Four-stroke diesel - 25 kg 3.1 0.12 8.1 1 3.1
EL 308 (old) 2T Otto 3000 30 kg 4.5 0.15 6.66 1 4.5
DENQBAR 4T Otto - 17 kg 4.8 0.28 3.5 1 4.8
Delta Hawk V Two-stroke diesel 2650 142 kg 135 0.95 1.05 4th 33.75
Shepherd 3702 2T Otto 5000 45 kg 65 1.44 0.7 3 21.66
FE (3.46 cm³) Two-stroke glow igniter 32000 0.45 kg 1.4 3.1 0.32 1 1.4

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## literature

• Hans-Hermann Braess, Ulrich Seiffert: Vieweg manual automotive technology. 2nd edition, Friedrich Vieweg & Sohn Verlagsgesellschaft mbH, Braunschweig / Wiesbaden, 2001, ISBN 3-528-13114-4 .

## Individual evidence

1. Maximum power-to-weight ratio for trucks, buses, etc. Ä .: § 35 StVZO
2. Motorization - time series 2003 to 2012; New car registrations ( Memento of the original from November 22, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , kba.de, accessed on November 23, 2013
3. Keating Bolt Specifications ( Memento of the original from May 23, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , keatingsupercars.co.uk, accessed May 11, 2015
4. Keating TKR Specifications ( Memento of the original from January 11, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , keatingsupercars.co.uk, accessed March 7, 2015
5. Data from the Benetton B186 BMW , ultimatecarpage.com, accessed on May 20, 2013
6. Data from the Red Bull Racing RB8 Renault , ultimatecarpage.com, accessed on May 20, 2013
7. Technical data Porsche 956 C) , Porsche.de, accessed on May 24, 2013
8. Technical data of the Golf VII GTI , volkswagen.de, accessed on May 19, 2013
9. Corsa Technische Daten , Opel.de, accessed on May 20, 2013