Vehicle metrics
From Wikipedia, the free encyclopedia
There are a broad range of metrics that denote the relative capabilities of various vehicles. Most of them apply to all vehicles while others are type-specific.
| Measurement | Imperial unit | Metric unit | Affects | General preference | Notes |
|---|---|---|---|---|---|
| 0 to 60 mph | seconds | seconds | acceleration | lower is better | |
| Braking distance | feet | meters | safety | shorter is better | |
| Brake specific fuel consumption | ? | g/kWh | economics | lower is better | |
| Drag coefficient | (ratio) | (ratio) | economics, top speed | lower is better | |
| Fuel economy | mpg | L/100 km | economics | greater is better (mpg), lower is better (L/100 km) | must be specified on new vehicles for sale in the US |
| Ground pressure | psi | Pascal | traction | lower is better in soft ground, reduces bogging | has greater impact on off-road vehicles |
| Lift to drag ratio | ? | ? | economics | higher is better | improved by narrow, long wings |
| Power-to-weight ratio | hp/lb | W/kg | acceleration | higher is better | |
| Roll center | ? | ? | handling | lower is better | |
| Rolling friction | ? | ? | economics | lower is better | improved by narrow, high pressure tires |
| Specific fuel consumption (thrust) | lb/lbf h | kg/kgf h or g/(kN·s) | economics | lower is better (for any given speed) | in airbreathing jet engines it is improved by using more inert air for propulsion (i.e. lower exhaust velocity), in rockets, higher exhaust velocity |
| Specific fuel consumption (shaft engine) | lb/hp h | kg/kW h | economics | lower is better | for shaft engines less fuel use for a given output power means higher efficiency |
| specific impulse | seconds | seconds or kN s/kg | economics | higher is typically better | in airbreathing jet engines it is improved by using more inert air for propulsion (i.e. lower exhaust velocity), in rockets, higher exhaust velocity |
| Top speed | mph | km/h | Maximum rate of straight line travel | higher is better | Electronically limited in some cars for safety (mostly due to concerns of high speed tire failure) |
| Weight | lb | kg | acceleration, braking distance | lower is better | |
| Weight distribution | % | % | handling, acceleration, traction | close to 50:50 is usually better |
