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Vehicle metrics: Wikis

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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 English unit Metric unit Affects General preference Notes
0 to 60 mph seconds seconds acceleration lower is better
0 to 100 to 0 mph seconds seconds acceleration & braking lower is better formerly common in British publications
Braking distance feet meters safety shorter is better
Brake specific fuel consumption lb/(hp·h) g/(kW·h) economics lower is better
Drag coefficient (ratio) (ratio) economics, top speed lower is better
Frontal cross-section area ft2 m2 economics, top speed lower is better if area is too small, vehicle becomes difficult to use
Fuel economy mpg l/100 km and km/l economics greater is better (mpg and km/l), lower is better (L/100 km) must be specified on new vehicles for sale in the US
Maximum g-force(s) g or ft/s2 g or m/s2 acceleration higher is usually better measures cornering, braking or forward acceleration
Ground pressure psi pascals traction lower is better in soft ground, reduces bogging; higher with loose surface has greater impact on off-road vehicles
Lift to drag ratio - - economics higher is better for aircraft improved by narrow, long wings
Power-to-weight ratio hp/lb W/kg acceleration higher is better
Polar moment lb·ft2 kg·m2 handling lower permits quicker turn-in for cars, higher is more stable in straight line. The moment of inertia about a vertical axis of a vehicle
Propulsive efficiency  %  % economics higher is better For rockets and aircraft, percent of the energy contained in a vehicle's propellant converted into useful energy,
Roll center inches mm handling Too many variables to state a general preference.
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 tire failure at high speed)
Weight lb kg acceleration, braking distance lower is better
Weight distribution  %  % handling, acceleration, traction close to 50:50 (%Front:%Rear) is commonly considered better
Gross axle weight rating lb/axle kg/axle durability, economics larger is better for vehicles carrying loads Ultimately limited by the hardness of the road surface and legal limits intended to limit damage to it
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