Reading Technical Chart Of An Automobile

When you read the specifications or “specs” of a car’s performance, do you find yourself completely baffled?
In these post, I will try to explain what does a Technical  Specifications chart means to a layman.

Let's get straight to some definitions

Horsepower-                                                                                                                     

A horsepower is a totally arbitrary measurement – dreamt up by  James Watt when trying to compare the effectiveness of his steam engines against the horses they were replacing.                                                                                                                     

What does this mean to you? Simply put, the higher the horsepower, the stronger a car’s engine. For example, if you are looking at two identical cars in weight and form, but one has an engine with higher horsepower, this car will be faster.

Let’s understand the technical stuff
Horsepower = Torque *Rpm/5252
1 Horsepower = 550 foot pounds per seconds (ft-lbs /sec)
or 
1 Horse power =746 watts
Why 5252?
Thus in order to calculate the horsepower in terms of torque and rpm, we use this above formula and we get this magical no 5252 after page long math calculations.Thus by knowing the torque at the wheel and the rpm at which the torque was measured and plugging it into the above equation one can find out the resultant horsepower.
Torque:
Torque tells you at what rate the power of an engine is delivered. It can be basically defined as the amount of twisting force a crankshaft can produce while it is turning. For cars, it can be described as the pulling power of the car’s engine. The higher the torque, the more responsive a car is to either starting (from a standstill point) or at any point while the car is on the road. The more the torque the more power you have at hand at any moment from any range or RPM’s (revolutions per minute). RPM’s is what you see next to your speedometer, measured in thousands.

Let’s understand it better
Torque is force applied times the perpendicular distance.

Torque= force*distance

 (perpendicular to the axis of the reference point)                                                 Consider a scenario in which one has to take out the axle nut

 we can use this example to understand the Torque                                                                                   as torque= force*perpendicular distance                                                     we take a  pry bar of length 1m and if we apply the force of say 50N . Then we can say that the torque is 50Nm.(The pry bar should be exactly perpendicular.)

suppose we apply a force of 25N then we have to increase the length of the pry bar 2m in order to produce the same amount of torque.
 Thus varying the force and distance one can change the values of torque.

Coming back to our engine performance part let’s say a particular car produces a torque of 115Nm@4000rpm i.e it is the peak torque that is available .That means it is the maximum twisting force that is produced at the wheels. Thus by using the force produced by the engine and running it through different gears we get different torque .
However there are some limitations to that ,you cannot link up bigger and bigger gears in your transmission to get more torque because it will result in lower rpm as the gears are big and thus the rpm of the output shaft that comes out of your engine also goes down as well thus resulting in less overall speed.
(Remember the torque produced at the crankshaft will be more than what you receive at the wheels as there will be some transmission loss and some losses due to friction.)

Bonus point-

On the other hand, of you apply torque in a particular direction, while the thing is rotating in opposite direction, you are doing negative work. e.g. brakes

Lastly

The torque and the rpm curves cross each other exactly at 5252 rpm. And that’s how horsepower is calculated from torque and rpm.



Hope you understood the topic very well in case of any doubts feel free to ask in the comment section .And as always thanks for reading.


Note -