tryg
New Member
This may be the most highly debated question in all automotive internet forums.
It's not that the definitions are in doubt. They're obviously objective. The controversy centers around which is more important.
Torque
Torque is defined as the force at any one point on the edge of a circle in the exact direction of the rotation multiplied by the radius (distance from the center). This comes from the calculus/geometry concept of a "tangent", a line which touches exactly one point of the edge of a circle.
In the metric system, force is calculated in newtons, and distance is in meters, so the standard torque unit is Newton-Meters or N-M.
Horsepower
Horsepower is a unit of power. It can be defined in many ways. In its basic sense, it's defined as work done in a straight line as described above under "Power". But when the work is not done in a straight line, it must be defined in a different way: torque.
The mistake most people make when engaging in this debate is considering horsepower and torque independently. Almost everyone argues as if they are separate, unrelated values. They aren't.
Horsepower = Torque X RPM / 5252
This equation is the most important thing on this page, and it's the reason that anyone telling you that horsepower and torque should be considered equally and separately is significantly off-base. The fact of the matter is that horsepower is the product of torque and another value -- RPMs (divided by 5252). It's not unrelated, separate, or different.
In fact, there's not a single machine in existence that measures a car's horsepower. It's a man-made number. When a car's performance is tested, it's torque is measured using a dynamometer. The measure of an engine's performance is torque. Horsepower is an additional number that's attained by multiplying the torque by the RPMs.
Gearing=win
Now when it comes to just about any type of racing known to mankind, besides engine output, gearing is the single most contributor to acceleration. It will make or break any car and the right gear selection can and will mean the difference between winning and losing a race.
How important is gearing? Gearing nearly makes torque obsolete. Yes, it's that important. In a perfect environment with no limiting factors such as size and weight, the actual peak torque output of an engine would be totally meaningless because of gearing.
How's that possible? It's simple. Gearing multiplies peak torque to the wheels to any amount desired. Increasing the ratio increases torque.
The limiting factors are the biggest problem with this ideal setup. Torque is multiplied through gear ratios, but the higher the gear ratio, the larger the gear and the more space it takes up. Unfortunately, in the real world, there's only so much space for a gear to occupy. It's this space limit that contributes to the "torque = towing capacity" philosophy. If space were unlimited and we could make the ratios anything we wanted, then towing capacity would be limitless since we could easily just utilize a higher ratio gear.
Horsepower and Torque "At the Wheels"
Now when we're talking about cars, the amount of horsepower or torque generated at the flywheel is not very useful when determining acceleration. What is useful, however, is horsepower and torque "at the wheels". The problem here is that drivetrains cannot be perfectly efficient and pass 100% of the power of the engine through its components to the wheels.
Some of the power is lost for several reasons. Generally 15-25% of engine power never makes it to the wheels. Different types of drivetrains will have different levels of efficiency. Generally, drivetrains with more weight and those with more components will be less efficient.
Notes
- Gearing is extremely important because it controls RPMs (and therefore horsepower).
- Gears magnify torque -- hence the acceleration available in first gear.
- Racecars have high horsepower due to high RPMs, not due to high torque.
- Below 5252 RPMs any engine's torque will always be higher than its horsepower, and above 5252 RPMs any engine's horsepower will always be higher than its torque. At 5252 RPMs the horsepower and torque will be exactly the same.
- It is better to make torque at high rpm than at low rpm, because you can take advantage of gearing.
It's not that the definitions are in doubt. They're obviously objective. The controversy centers around which is more important.
Torque
Torque is defined as the force at any one point on the edge of a circle in the exact direction of the rotation multiplied by the radius (distance from the center). This comes from the calculus/geometry concept of a "tangent", a line which touches exactly one point of the edge of a circle.
In the metric system, force is calculated in newtons, and distance is in meters, so the standard torque unit is Newton-Meters or N-M.
Horsepower
Horsepower is a unit of power. It can be defined in many ways. In its basic sense, it's defined as work done in a straight line as described above under "Power". But when the work is not done in a straight line, it must be defined in a different way: torque.
The mistake most people make when engaging in this debate is considering horsepower and torque independently. Almost everyone argues as if they are separate, unrelated values. They aren't.
Horsepower = Torque X RPM / 5252
This equation is the most important thing on this page, and it's the reason that anyone telling you that horsepower and torque should be considered equally and separately is significantly off-base. The fact of the matter is that horsepower is the product of torque and another value -- RPMs (divided by 5252). It's not unrelated, separate, or different.
In fact, there's not a single machine in existence that measures a car's horsepower. It's a man-made number. When a car's performance is tested, it's torque is measured using a dynamometer. The measure of an engine's performance is torque. Horsepower is an additional number that's attained by multiplying the torque by the RPMs.
Gearing=win
Now when it comes to just about any type of racing known to mankind, besides engine output, gearing is the single most contributor to acceleration. It will make or break any car and the right gear selection can and will mean the difference between winning and losing a race.
How important is gearing? Gearing nearly makes torque obsolete. Yes, it's that important. In a perfect environment with no limiting factors such as size and weight, the actual peak torque output of an engine would be totally meaningless because of gearing.
How's that possible? It's simple. Gearing multiplies peak torque to the wheels to any amount desired. Increasing the ratio increases torque.
The limiting factors are the biggest problem with this ideal setup. Torque is multiplied through gear ratios, but the higher the gear ratio, the larger the gear and the more space it takes up. Unfortunately, in the real world, there's only so much space for a gear to occupy. It's this space limit that contributes to the "torque = towing capacity" philosophy. If space were unlimited and we could make the ratios anything we wanted, then towing capacity would be limitless since we could easily just utilize a higher ratio gear.
Horsepower and Torque "At the Wheels"
Now when we're talking about cars, the amount of horsepower or torque generated at the flywheel is not very useful when determining acceleration. What is useful, however, is horsepower and torque "at the wheels". The problem here is that drivetrains cannot be perfectly efficient and pass 100% of the power of the engine through its components to the wheels.
Some of the power is lost for several reasons. Generally 15-25% of engine power never makes it to the wheels. Different types of drivetrains will have different levels of efficiency. Generally, drivetrains with more weight and those with more components will be less efficient.
Notes
- Gearing is extremely important because it controls RPMs (and therefore horsepower).
- Gears magnify torque -- hence the acceleration available in first gear.
- Racecars have high horsepower due to high RPMs, not due to high torque.
- Below 5252 RPMs any engine's torque will always be higher than its horsepower, and above 5252 RPMs any engine's horsepower will always be higher than its torque. At 5252 RPMs the horsepower and torque will be exactly the same.
- It is better to make torque at high rpm than at low rpm, because you can take advantage of gearing.
