What is Torque in a car?

"How do you measure Torque?"

Torque is simply a measure of power. It explains how much push a car gives or the turning power of the engine.

If you had a lever attached to the center of a wheel the Torque is the amount of force you could use to pull on that handle to rotate the wheel.

Torque is an angular force (although through an infinitely short arc it can be considered to be linear) but is still acting about a center of rotation.

Torque in a car is measured in nm (newton meters) or ft-lb / lbft / lbf-ft (pounds per foot) - NB people quote torque as lbft, ftlb, lb-ft and ft-lb but these can be regarded as one and the same.

All terms will interchange quite safely lbf likewise is fine, although possibly might be mistaken for pounds force which is a linear force.

What is the difference between BHP and Torque?

BHP shows how quickly you hit a wall and torque indicates how far through it you get.

Do not confuse Torque with BHP as they are different although both related to the power of a car. So what is Torque then and how does it compare with horsepower or BHP?

Horsepower = Torque x rpm/5252
Torque = Horsepower x 5252/rpm

Any Power/Torque graph you see will cross at 5252 provided you measure engine speed in revs per minute, torque in lbft, and power in BHP. (*see below for an explanation of this.)

What does Torque tell me about an engine

In an engine, the quoted Torque figure is just the peak figure the engine can attain. This is only a small part of the story.

220ft-lb at 8000rpm is the turning force that can be exerted at 8000rpm.

Let's look at a complete Dyno graph to get an idea of this measure of a cars power.

dyno-plot

You'll note the torque peaks at 4000rpm and then tails off.

So the engine is pulling the hardest at this point.

In some cars the power builds gradually, TorqueCars prefer a nice flat torque band that covers most of the RPM range, which means you have plenty of in-gear acceleration.

As the torque tails off around 5500 to 6000 you should really change gear here to drop down the RPM range and hit the higher Torque Band.

Why does Torque and BHP cross at 5252 on the dyno graph?

To begin, we should start with a gentleman named James Watt. He is the one who developed the entire idea of a "horsepower" and of course, the SI unit of power, the watt.

Watt suggested that per second the average horse worked at a rate 550 foot lbs, or 33,000 foot lbs per minute. Imagine a horse pulling a weight up a vertical mine shaft.

This means that on average, a horse could move 33,000 lbs 1 foot distance in 1 minute. So 1 hp=33,000 foot lbs per minute.

Now, since we're talking about engines, work is being applied to a rotating crankshaft. This means that we need to talk about torque.

But what does a ft-lb of torque mean? Well, it means that we have a 1 lb weight attached to a weightless bar 1 foot from the fulcrum.

Now imagine that bar is rotated a full turn 360 degrees. The distance traveled is the circumference of the circle, which is 2*radius*pi, which equals 6.28319 ft.

So one rotation is 6.28319 ft in distance and we know that 6.28319 ft-lbs of work (torque) was done.

Watt figured out that 1 hp=33,000 ft-lbs of work per minute. If we divide 33,000 by 6.28319, we arrive at 5,252.1. This means that for every 5,252 revolutions per minute of 1 ft-lb of torque, we get 1 hp.

The 5252 mentioned is unitless, simply forming part of the calculation for determining power from torque and revs on a dyno graph it happens to be RPM.

Formula to calculate Torque or HP

To work out either HP or Torque :-
Horsepower = Torque x rpm/5252
Torque = Horsepower x 5252/rpm

So a Dyno measures Torque & then uses the equation to calculate horsepower.

When you look at a torque graph you get a feel for where the power range of an engine is and can work out the optimum gear shift points.

Check out my YouTube channel, we're regularly adding new content...


PLAY VIDEO

PLEASE HELP: I NEED YOUR DONATIONS TO COVER THE COSTS OF RUNNING THIS SITE AND KEEP IT RUNNING. I do not charge you to access this website and it saves most TorqueCars readers $100's each year - but we are NON PROFIT and not even covering our costs. To keep us running PLEASE Donate here

If you liked this page please share it with your friends, drop a link to it in your favourite forum or use the bookmarking options to save it to your social media profile.

Feedback - What do You Think?

Please use our forums if you wish to ask a tuning question, and please note we do not sell parts or services, we are just an online magazine.

Help us improve, leave a suggestion or tip

Your Constructive comments on this article, I really want to improve this article with your help and suggestions.


Please watch this video and subscribe to my YouTube channel.



3 Responses to “Torque in a car engine”

  1. charger69 says:

    Explnations are awesome done and it’s obvious they are made from a person skilled in this field. What would be great is to add pictures by showing what torque is thru drawings and so, so non english and people with less knowledge will understand it better. Great work!!!

  2. Hunting.Targ says:

    This is interesting, though it feels a bit technical for a general audience. A couple illustrations of the horse pulling a weight up a shaft via pulley, and also pulling a weight along a tiny planet on pulleys (such that the weight is on the opposite side from the horse and the rope is close to circular) I think would be helpful. It is mechanical physics, after all, and most people do not understand science through strictly words, or strictly equations.
    Cheers!

  3. BOB FEARICK says:

    New to torque cars, I think it is educational information

Member Benefits

Join our forum today and benefit from over 300,000 posts on tuning styling and friendly car banter.

You will also have full access to the modifed car gallery, project car updates and exclusive member only areas.

(All car owners of all ages and from all countries are welcome).


BMW 335i - 2021 COTY

We gave the BMW 335i our coveted car of the year award, read more about this awesome car and see why 335i Tuning Guide

Tips for N54 Tuning

Tips for N55 Tuning

Popular articles

Diesel Tuning
ECU Remapping
double clutching
Induction Kits
Customize a car
Chip Tuning
Modded Car insurance
Track day insurance cover
Remap Diesels
Calculate MPG
Unblock a DPF
Tuning in Forza


Turbo Tuning

What is a turbo and how does it work
Read more...

Water Injection

Benefits and drawbacks of engine water injection systems
Read more...

Car Styles

Definitions of car styling looks
Read more...

Re Upholstery Cars

Re-upholstery for your car from seats to dashboard.
Read more...

Converting A Car To Ev

Converting a car to EV
Read more...

French Low Emission Zone Permit Scams

French Low Emission Zone Permit Scams
Read more...

MPG Calculator

MPG calculator UK miles per Gallon – calculate MPG
Read more...