Ask a Technician: What is Torque and Why Does it Matter?

The chances are that if you have been reading a review of any modern car, you will have spotted the word 'torque' mentioned by the writer. You may also have wondered exactly what it meant. The answer is relatively simple.

Normally shown in pound-feet, torque is a means of measuring the relative performance of a car. In fact, it actually measures the turning power of the car, but can be more easily understood in non-vehicular terms.

Imagine that you have a 1-pound weight bolted to the floor. If you try and lift that weight (with any degree of force) then you will have exerted power, but no movement will have occurred. If the weight is unbolted, and you apply enough force to lift the weight 1 foot into the air, then 1 pound-foot of work will have been done. If it took a minute to lift that weight, then the measurement would have been 1 pound-foot per minute.

So how does this relate to a car? Well, the more power that you are able to apply to that weight, the quicker and more easily you will be able to lift it. In simple terms, therefore, the more pound-feet of torque that your car's engine is able to deliver, the more available power it has to accelerate because it can turn the wheels more quickly.

It isn't quite as simple as that, as other factors influence the torque measurement. The engine torque is also directly related to the torque on the wheel by the gear ratio. If the total gear ratio is 10:1 (which means that 10 revolutions of the engine result in one revolution of the wheels) then the torque exerted by the wheels is increased by a factor of 10 compared to the engine.

It is worth noting that a car will accelerate at its hardest at its torque peak within any given gear. Below or above that peak, it will not accelerate as quickly. In a low gear, the torque available will normally be quite a lot higher than the engine output torque. However, at a lower gear, the engine must turn faster to make the car move the same speed. To accelerate quickly from a standstill requires a lot of power at low engine revolutions per minute (rpm). The higher the pound-feet torque measurement on a car, therefore, the better its accelerative capability at lower rpms.

As such, torque is an important measurement for drivers that are looking for high-performance models, with rapid acceleration. Torque is the only measurement of performance that a driver can actually 'feel' but is also complemented by the car's brake horsepower.