Power to Weight Ratio

[Lord & Master]

how is it calculated
& it should be Weight to Power Ratio
if the lower the number the more faster the car is

[HondaNSX]

Power-to-weight ratio is a measure commonly used when comparing various vehicles (or engines), including automobiles, motorcycles, aircraft, and armoured fighting vehicles. It is, simply, the power the engine develops, divided by the vehicle's (or engine) weight.

The power-to-weight ratio is often used as an indication of likely accelerative performance. Vehicle weights have relatively little impact on top speed, which is mostly dependent on aerodynamic drag (see drag equation). Acceleration, on the other hand, is dominated by the Newtonian acceleration term, F = m×a, so more force (F - from the engine's torque delivered to the driven wheels or thrust delivered by an aircraft engine), will deliver more acceleration (a) for any given vehicle mass (m = weight/g).

In any vehicle the engine power-to-weight ratio is essential for vehicle power-to-weight ratio. But in an aircraft it's more critical than in any other vehicle because any additional weight requires more lift to be generated by the wings in order to lift it. More lift from the wings automatically means more drag, through a process known as induced drag, slowing the plane down. Thus if any two engines deliver the same power, the lighter one will result in a better plane. Power-to-weight ratio therefore has a much more important impact on overall performance in aircraft, including top speed.

In this usage the power-to-weight ratio is typically used to refer to the weight of the engine alone, as a useful way of comparing various aircraft engines. The term applying to the aircraft as a whole is power loading, and is used especially in helicopter engineering.

Power-to-weight ratio is also often used as a general indicator of the mobility of tanks and other armoured fighting vehicles, usually expressed in horsepower per tonne (hp/t). Such vehicles, weighing up to seventy tons, must be able to achieve relatively high speeds quickly, while overcoming a great deal of inertia and mechanical resistance even on hard surfaces, and also travel at high speeds over soft ground and up steep slopes.

found it on some web site, but enjoy

[lightweight]

great explanation!!

I wanted to add that if we have 2 cars with the same power to weight ratio and the first one has 100 hp and the second has 200 (random numbers chosen, just to make a point), then the 100 hp car will be faster in low-speed accelleration and the 200 hp car will be faster in high speed acceleration

[deffenbaugh03]

great explanation!!

I wanted to add that if we have 2 cars with the same power to weight ratio and the first one has 100 hp and the second has 200 (random numbers chosen, just to make a point), then the 100 hp car will be faster in low-speed accelleration and the 200 hp car will be faster in high speed acceleration

Explain why is that?

EDIT: So you're saying if i have a car with 100hp which weighs say 1000kg but yet has a very slow unresponsive engine it will be faster in low speed accelaration than a car with 200hp which weighs 2000kg yet has highly responsive engine or an engine which makes really good low torque? Makes no sense to me there are way too many factors.

[KnifeEdge_2K1]

great explanation!!

I wanted to add that if we have 2 cars with the same power to weight ratio and the first one has 100 hp and the second has 200 (random numbers chosen, just to make a point), then the 100 hp car will be faster in low-speed accelleration and the 200 hp car will be faster in high speed acceleration

thats just not true

acceleration is depended on torque at the wheels, you dont know jack shit unless you know the torque curves (or a reasonable approximation) and gear ratios of the car, aerodynamic drag is also a factor

at top speeds the 100hp car might be faster then the 200hp car if the 200hp car is as aerodynamic as a piece of shit

[deffenbaugh03]

at top speeds the 100hp car might be faster then the 200hp car if the 200hp car is as aerodynamic as a piece of shit

Actually a piece of sh*t would be pretty aerodynamic
sort of like a rocket only a little less round

[lightweight]

Explain why is that?

EDIT: So you're saying if i have a car with 100hp which weighs say 1000kg but yet has a very slow unresponsive engine it will be faster in low speed accelaration than a car with 200hp which weighs 2000kg yet has highly responsive engine or an engine which makes really good low torque? Makes no sense to me there are way too many factors.

Actually I was not referring to engine speed, I was referring to km/h.

For example, take an caterham and an RX7 with identical p to w ratios. The cateraham would beat the rx7 off the line, but after 150 or so km/h the rx7 will approach and then pass

[lightweight]

thats just not true

acceleration is depended on torque at the wheels, you dont know jack shit unless you know the torque curves (or a reasonable approximation) and gear ratios of the car, aerodynamic drag is also a factor

at top speeds the 100hp car might be faster then the 200hp car if the 200hp car is as aerodynamic as a piece of shit

You are entering more factors in the equation. I am examining the effects of P to W ratio in acceleration. Only these two variables change. The analysis is ceteris paribus.

[Matra et Alpine]

You are entering more factors in the equation. I am examining the effects of P to W ratio in acceleration. Only these two variables change. The analysis is ceteris paribus.

yet tyhe examples you gave above were of cars with radically different frontal area and Cd factors.

You woudl do well to consider the differing engines in the SAME vehicle.

For example take a 1300 X flow and a 1600X-flow Caterham.
plenty around, many raced, plenty of evidence.

The 1300 is slightly lighter and lower power but does NOT achieve faster accleration but DOES have less top speed as the power limits the force to overcoem teh squuaring of teh aero drag.

I suspect you were missing weight equivalency in yrou inital comments.