Clarify power to weight ratio?

[Gsir8]

How do you figure out the power to weight ratio, and which is better, lower or higher?

 

[TheWizard]

Power to weight ratio is the ratio between the power that your vehicle has and its weight. The higher the number, the better. For example if your car has 300HP and weights 1000 pounds, the power to weight ratio is 0.3 HP/pound, which means that your car outputs 0.3 HP for every pound it weighs. However, if another car has 300HP but only weighs 500 pounds, the power to weight ratio would be 0.6 HP/pound (twice as much as the other car), which would mean that this car outputs 0.6 HP for every pound it weighs. The reason why a higher number is better is because, for a given value of horsepower, the less the car weighs the more/better that power is used - a car that weighs less has less inertia, it's easier to accelerate, and to change its direction. On the other side, it has less traction, as traction depends on friction, which in turns depends on weight. But that's a whole different story, so I'll stop here.

Hope this helps.

EDIT: HOWEVER, what is listed in the Specs section in GT3 as Power Weight Ratio is not the Power to weight ratio, but exactly the reciprocal of that. In other words, it is the WEIGHT TO POWER Ratio. Here, the smaller the number, the better. Using the above example, the first car would have 3.333 pounds/HP while the second car would have 1.667 pounds/HP, which, for the reasons explained above, is better than the first car. So, if you were referring to GT3 Specs, since what is listed there is the WEIGHT TO POWER (not the Power to Weight) Ratio, the smaller the number, the better.

The Wizard.

 

[JNasty4G63]

Also, a lot of time they list it as "pounds per hp" so don't be fooled. Just depends on how its worded.

Pounds/HP
Small number is good. Meaning you have less weight per each horsepower to push around.

HP/Weight
Large number is good here. Like was said before me, a larger number here means that your car again has more power per each horsepower.

Just depends on how its worded.

Hilg

 

[MrktMkr1986]

How do you figure out the power to weight ratio, and which is better, lower or higher?

Take the power of the car and divide it by the weight of the car (in order to find the weight-to-power ratio, which is more popular). This is the number you are more likely to find in automotive publications.

For example:

Dodge Viper SRT-10:

Curb weight: 3,385lbs
Horsepower: 500 horsepower

3385
500

and you get a weight-to-power ratio of 6.77, where 6.77 represents the amount of weight each horsepower is pushing. In this case, the lower the number the faster the car, in general. Weight-to-power ratios are not 100% indicative of a cars performance because there are other factors involved that determine a cars performance. Factors such as aerodynamics, gear ratios, the drivers weight and skills, weather conditions, the condition of the road, the conditions of the tires being used, tire pressure, and how old/new the car is just name a few. Also, weight-to-power ratios don't take into account the amount of torque a car has. For example, though you may be able to find another car with a weight-to-power similar to that of the Viper, (Lamborghini Gallardo), the Viper has 525 lb./ft of torque where the Gallardo "only" has 376 lb.ft. of torque. You also have to take into account the fact that car companies "advertised" horsepower figures are never accurate. For example, though Honda quotes 240 horsepower for its S2000, in reality its making closer to 260. The same holds true for Lexus. Though their SC430 is rated at 300 horsepower, it's actually closer to 250, if that. So when calculating w/p ratios, try to use numbers from a dyno and not from the manufacturer. The examples below assume the manufacturer's data is accurate...

List of other cars w/p ratio:

2004-2005 model cars
Acura NSX - 10.87
Acura NSX automatic - 12.69
Audi A4 1.8T Cabriolet CVT - 21.4
BMW 645Ci Coupe 6-speed - 11.67
Cadillac Escalade AWD - 16.15
Ferrari 612 Scaglietti F1 - 7.51
Ford Mustang SVT Cobra - 9.7
Honda S2000 - 11.81
Hyundai Accent GT - 21.92
Jaguar XKR - 9.91
Lexus IS300 - 15.14
Mazda MX-5 Miata - 17.23
Mercedes-Benz CL65 AMG - 7.71
Mitsubishi Eclipse Spyder GS - 21.07
Nissan 350Z Track - 10.75
Pontiac GTO - 9.31
Porsche Carrera GT - 5.03
Saab 9-5 Aero - 13.88
Saturn ION 3 - 19.8
Scion tC - 18.16
Toyota MR2 Spyder - 15.91
Volvo V70 R - 12.52

 

[TheWizard]

Take the power of the car and divide it by the weight of the car.

For example:

Dodge Viper SRT-10:

Curb weight: 3,385lbs
Horsepower: 500 horsepower

3385
500

I don't mean to imply that what you say in the rest of your post is incorrect, but what you did there was taking the weight of the vehicle and divide it by its power, therefore getting the weight to power ratio. When somebody says "A" to "B" Ratio, it means exactly that, take the first one and divide it by the second one.

A to B Ratio =
A
B

However, as I said in my first post, if what you are looking for is the Weight to Power Ratio, then you take the weight of the car and divide it by the amount of horsepower. In this case, the higher the number the better.

Nothing personal/no hard feelings or anything/not saying you are a/an [instert random insult here]/not meaning to start a war

EDIT: substitute higher with lower. Sorry, that was a typo.

The Wizard.

 

[MrktMkr1986]

I don't mean to imply that what you say in the rest of your post is incorrect, but what you did there was taking the weight of the vehicle and divide it by its power, therefore getting the weight to power ratio. When somebody says "A" to "B" Ratio, it means exactly that, take the first one and divide it by the second one.

A to B Ratio =
A
B

However, as I said in my first post, if what you are looking for is the Weight to Power Ratio, then you take the weight of the car and divide it by the amount of horsepower. In this case, the higher the number the better.

Nothing personal/no hard feelings or anything/not saying you are a/an [instert random insult here]/not meaning to start a war

The Wizard.

It's cool. I'll just change the wording.

 

[Duke]

Americans commonly use the Weight/Power ratio, but usually call it the 'power-to-weight' ratio, just to confuse things. So from an American source, you want to see a low number, meaning each horsepower is pushing fewer pounds.

Metric parts of the world, on the other hand, actually do use the Power/Weight ratio, so they are looking for big numbers, meaning each tonne of car is being pushed by more horsepower.

 

[TheWizard]

It's cool. I'll just change the wording.

I am glad you took it with the proper spirit

Americans commonly use the Weight/Power ratio, but usually call it the 'power-to-weight' ratio, just to confuse things. So from an American source, you want to see a low number, meaning each horsepower is pushing fewer pounds.

Metric parts of the world, on the other hand, actually do use the Power/Weight ratio, so they are looking for big numbers, meaning each tonne of car is being pushed by more horsepower.

Cool, something else new I learnt today. I didn't know that Americans used the Weight to Power Ratio. As for me, being a bloody Italian, I belong to the "metric part of the world"

Having seen both ends of the spectrum (English Engineering System - as I study here in the States / International System - as I was born in Italy and lived there for 22 years of my life), I can't even begin to stress the advantages of "The powers of 10" system, but I don't want to push my luck to far ~ this would turn into a war in a matter of nanoseconds (just to remain on topic - nano = 10^-9)

The Wizard.

 

[Duke]

Believe me, the rational part of me wants to think in metric, but the subconcious part of me can't do it naturally yet.

For that matter, I've always wondered why a 'day' isn't made up of 20 100-minute hours...

 

[MrktMkr1986]

I am glad you took it with the proper spirit

I'm peaceful by nature.

Having seen both ends of the spectrum (English Engineering System - as I study here in the States / International System - as I was born in Italy and lived there for 22 years of my life), I can't even begin to stress the advantages of "The powers of 10" system, but I don't want to push my luck to far ~ this would turn into a war in a matter of nanoseconds (just to remain on topic - nano = 10^-9)

The Wizard.

I agree, the metric system does have its advantages over the English system. However, there are drawbacks. For example, my transmission, the "A4LD" started life originally as a C3 automatic transmission built in America. It was shipped to France where all the measurements etc. were changed from the English system to the metric system and then sent back as "new" transmission.
The result: one of the worst automatic transmissions ever built... and I have the leaky line fittings to prove it!

 

[TheWizard]

For that matter, I've always wondered why a 'day' isn't made up of 20 100-minute hours...

Don't want to sound like a "know it all" here, but I believe time is based on the sexagesimal system (Base 60) because "back in the days" (can't really be bothered to look up WHEN ) they (can't really be bothered to look up WHO) divided the apparent motion of stars and planets in angles (degrees, minutes, and seconds) and again "they" used to tell time by how long it would take the Sun to cover a certain amount of its path in the sky.

Regarding getting used to think in a different system than your own, it's all a matter of time/experience/practice with the new system. I used to HAVE to convert everything in my head from English System to Metric System if I wanted to have a clue about a certain quantity, when I first came here. Now I can think in both systems and I am able to figure out a quantity even if it is given in English units, without having to convert it to Metric. It is still easier to go from one quantity to another WITHIN the Metric system though, as all you have to do is multiply by powers of 10, but the English system is no more that big of a problem for me. In addition, being an Engineer I need to know and be confortable in both systems, so I can't really complain now, can I?

The Wizard.

 

[TheWizard]

I'm peaceful by nature.

Me too

I agree, the metric system does have its advantages over the English system. However, there are drawbacks. For example, my transmission, the "A4LD" started life originally as a C3 automatic transmission built in America. It was shipped to France where all the measurements etc. were changed from the English system to the metric system and then sent back as "new" transmission.
The result: one of the worst automatic transmissions ever built... and I have the leaky line fittings to prove it!

Looks like in (that particular place in) France they need a new set of engineers, namely one that can CONVERT from one system to the other. But screwing up a transmission that goes in a car isn't (relatively) as bad as doing all the measurements in one system and then building the part as if those measurements had another system's units... and doing it in an aerospace vehicle... and this actually happened! Not making any names here, but if you think hard enough you all can figure out what agency I am talking about... lol!

Here is a quote from the actual article, have a laugh :

The peer review preliminary findings indicate that one team used English units (e.g., inches, feet and pounds) while the other used metric units for a key spacecraft operation. This information was critical to the maneuvers required to place the spacecraft in the proper Mars orbit.

The Wizard.

 

[MrktMkr1986]

Me too
Looks like in (that particular place in) France they need a new set of engineers, namely one that can CONVERT from one system to the other. But screwing up a transmission that goes in a car isn't (relatively) as bad as doing all the measurements in one system and then building the part as if those measurements had another system's units... and doing it in an aerospace vehicle... and this actually happened! Not making any names here, but if you think hard enough you all can figure out what agency I am talking about... lol!

Here is a quote from the actual article, have a laugh :



The Wizard.

I'm surprised it didn't fall out of the sky, crash, and burn...

 

[MrktMkr1986]

Back on topic:

My car '88 Ford Thunderbird Turbo Coupe has a weight-to-power ratio of about 16 based on its current modifications. My '94 Ford Mustang GT is about 15.5 for comparisons sake.

 

[TheWizard]

I'm surprised it didn't fall out of the sky, crash, and burn...

Ehm... it actually DID
Enough with the secrecy, here's the whole article:

A failure to recognize and correct an error in a transfer of information between the Mars Climate Orbiter spacecraft team in Colorado and the mission navigation team in California led to the loss of the spacecraft last week, preliminary findings by NASA's Jet Propulsion Laboratory internal peer review indicate.

"People sometimes make errors," said Dr. Edward Weiler, NASA's Associate Administrator for Space Science. "The problem here was not the error, it was the failure of NASA's systems engineering, and the checks and balances in our processes to detect the error. That's why we lost the spacecraft."

The peer review preliminary findings indicate that one team used English units (e.g., inches, feet and pounds) while the other used metric units for a key spacecraft operation. This information was critical to the maneuvers required to place the spacecraft in the proper Mars orbit.

"Our inability to recognize and correct this simple error has had major implications," said Dr. Edward Stone, director of the Jet Propulsion Laboratory. "We have underway a thorough investigation to understand this issue."

Two separate review committees have already been formed to investigate the loss of Mars Climate Orbiter: an internal JPL peer group and a special review board of JPL and outside experts. An independent NASA failure review board will be formed shortly.

"Our clear short-term goal is to maximize the likelihood of a successful landing of the Mars Polar Lander on December 3," said Weiler. "The lessons from these reviews will be applied across the board in the future."

Mars Climate Orbiter was one of a series of missions in a long-term program of Mars exploration managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO. JPL is a division of the California Institute of Technology, Pasadena, CA.

I know it's kinda, slightly off-topic, but... it's still funny anyway

The Wizard.

 

[MrktMkr1986]

Ehm... it actually DID
Enough with the secrecy, here's the whole article:

I know it's kinda, slightly off-topic, but... it's still funny anyway

The Wizard.

Oops...
*flips through Current Events for Dummies*

I figured it would anyway... anything that is created one way and then changed using another system of mesaurement is going to throw things off...

"Now where is that transmission repair manual?"

 

[retsmah]

Don't want to sound like a "know it all" here, but I believe time is based on the sexagesimal system (Base 60)

A quick google search came up with the Babylonians as being responsible, using a base 60 number system. So for them, having 1 minute = 60 seconds makes as much sense as having 1 minute = 100 seconds would to us.

Plus 360 is a nice number in a base 60 system, and that's pretty close to one year.

If we went to 100 seconds in a minute it would screw everything up, because the second is the base unit of time. So minutes would become longer, a day would be really effing long and nothing would match up nicely anymore.

The site I read said that the reasoning for a 60 second minute was the base 60 numbering system, im thinking that TheWizard's explanation makes more sense though, that base 60 came from observing how long days and years are.