Why is Torque Important in a vehicle?

The relationship between Horsepower and Torque – this is forever a subject of argument amongst car enthusiasts – there are those who claim that horsepower is the ultimate measure of power, whilst others will say that torque is vital for good acceleration. So whilst some will say if there is enough horsepower, there will be acceleration, others say that without torque, there will be little or poor acceleration. We are referring to cars, of course.

Actually, horsepower cannot exist without torque, because horsepower itself is the result of multiplying torque by rpm, divided by the number 5252. Don’t ask me why, but at 5252 rpm the horsepower and torque curve of any engine will cross each other, without fail. Thus the formula is as follows:- Horsepower = (Torque X RPMs)/5252.

We all know rpm means revolutions per minute, or how many times the crankshaft can turn in 60 seconds, but what is torque.

Torque is the amount of twisting force that is generated by the crankshaft as it is forced to turn round and round by the firing cylinders of the engine, and it started with a British measure called Foot-Pound. Simply put, one foot-pound is the rotational ‘force’ generated by hanging a one-pound weight at the end of a one foot wrench.

When we measure a car’s power, we use a ‘rolling road’ or a dynamometer, which actually measures the torque, and the engine revolutions; from here it estimates the engine horsepower, and they have values for the estimated power at the crankshaft, and at the wheels. Thus the measure of an engine’s performance is the torque it can produce – going back upwards on this article, we said that the torque is the amount of force the engine can generate (the rotational force generated by the engine, measured in Foot-Pounds). One ft-lb can be converted into metric terms by the factor 1.355818 to Newton Metres (Nm).

The horsepower is attained by multiplying the torque by the RPMs. In the same vein, based on the equation, we can see that torque also influences the horsepower value, thus it is quite common to have higher horsepower when there is more torque.

Let’s back-pedal to the age-old question – Which is more important for acceleration – Horsepower or torque?

You can say both are responsible, but more credit goes to torque, because torque results in horsepower. Let’s look at a live example – Let’s take the Honda Civic TC, which is equipped with a 1.5 litre turbo-charged engine; the TC delivers 171 horsepower and 220Nm of torque. In comparison the Honda Civic 1.8 has a 1.8 litre naturally aspirated engine that delivers 140 horsepower and only 174Nm of torque. The performance of both these engine types on the same body is very different, with the turbocharged engine easily outperforming the naturally-aspirated engine easily.

Turbo-charging contributes to the improved acceleration because of the more powerful ‘burn’ as a result of forced induction, and this directly increases the torque available. Gear reduction also works as a force ‘multiplier’ by increasing the mechanical advantage, but that is another subject. In this respect, even the wheel size makes a difference, as smaller wheels equate to higher mechanical advantage also, but all things being constant, it is the torque that matters.

In hybrid cars, the addition of an electric motor boosts up the total torque available, which accounts for the much improved performance figures usually reported. It is common to see mid-sized engine hybrid cars claiming performance figures equivalent to cars with 150 percent larger capacity engines due to the hybrid motor drive.

Pure electric cars also deliver massive amounts of torque, almost instantaneously, and we see that in the few fully electric cars available here currently. The biggest problem that electric cars face at the moment would be range anxiety (the fear of running out of battery in the middle of nowhere).

The latest scenario involves the soon-to-be-launched Honda City Hybrid. Whilst a conventional hybrid is basically a car with an engine that is ‘assisted’ by an electric motor that supplements power by 20 to 30 percent, the Honda City will be the first car here to use the i-MMD (intelligent Multi Mode Drive) system.

The difference between the i-MMD system and that of a conventional hybrid system is that the main drive to the car is through the electric motor, and the engine is a supplementary system to charge the batteries and help the propulsion at high speeds and when tackling slopes. The i-MMD system uses a motor that is capable of up to 320Nm of torque, and the particular one in the Honda City i-MMD hybrid is capable of 255Nm of torque, and that is more torque than is available in a 2.5 litre naturally aspirated engine. The way the system is built means that 255Nm of torque is available, all of the time with a few exceptions. These exceptions are the times when the engine takes over (at high speed) and at times when the car requires additional power.

I am waiting with bated breath to see just what this i-MMD system can do for the New Honda City, and also if it will be extended upwards through the product range, as Honda moves forward.